A publication devoted to the interests of the woollen manufacture,
while giving due prominence to its first raw material, wool, cannot
neglect the secondary materials which enter into finished fabrics. The
attractiveness and utility of the largest class of these fabrics are
due to the hue given them by the dyer; and of all the coloring
materials one of the most precious is indigo. In former times, as it
still does at the East, it occupied with madder the place of one of
the two most important of all dyeing materials. Forced of late years
to give way to the marvellous products of modern chemistry, it will
doubtless resume its place under the influence of a more enlightened
economy and a more subdued taste. To contribute to the hastening of
this return is one object of this essay. The most usual reproach
against American fabrics is the want of stability in our dyes,—a
reproach without justice, if applied to American fabrics alone; for
the cheapening of dyestuffs is practised in all the so-called
manufacturing nations, and is contemned alone in the East, from which
we have derived our arts, and by the people whom we despise as
barbarous. To remove this reproach from American fabrics would be
worthy of no little temporary sacrifice on the part of our
manufacturers.
The value of indigo as a dyeing material is due to the great stability
of the blue color, and the derivatives from blue, which it gives to
fabrics, especially of wool and cotton. It is not sufficient that a
dyed fabric should preserve its color when submitted to violent tests,
as when acted upon by vegetable or mineral acids or alkaline or soapy
baths: the only stable dyes are those which resist air and light, the
two destructive agents of vegetable colors. Indigo, from the
remarkable manner in which its color becomes fixed upon a fabric, to
be hereafter explained, possesses properties of resistance and
stability in a higher degree than any blue dye. And when we consider
that this blue has not only its own hue, but is the best foundation
for blacks, greens, purples, and even browns, the importance of these
properties cannot be over-estimated. Says M. de Kæppelin, a chemist
and manufacturer of Mulhouse, in one of a series of articles furnished
to the _Annales du gênie Civil_, 1864: “So high are the properties of
resistance and stability which indigo possesses, that it is perhaps to
be regretted for the art of the dyer and manufacturer of printed
calicoes, that the use of indigo becomes more and more rare, and that
the recent discoveries which modern science has placed at the service
of industry are daily eliminating it from our factories. I have
observed that whenever we have to dye stuffs of a high price, it is
indigo which always serves as a base for the foundation of all the
blue colors, or of those which are derived from blue. It is the same
for the fabrication of printed tissues, which serve for the poorer
classes, whose colors should have great stability without much
increase of cost. But of late years, especially, we find a tendency to
employ colors of little stability, and to prefer them, even in the
class of fabrics first referred to, to those which are more fast, on
account of their vivacity and freshness of tone. It is this tendency,
which the consumer partakes of even while complaining of it, that the
textile manufacturers ought to seek to combat. How often have I heard
the greatest manufacturers of Alsace deplore the obligation which they
felt that they were under of printing their tissues by means of colors
so fugacious and so little resistant as those composed from aniline.
We must hope, then, in the interest of that industry, that while
adopting the marvellous discoveries which science is every day making,
there shall be made a less general application of them, and that we
shall return to the fabrication of the styles which necessitate the
more constant employment of coloring materials,—less brilliant, it is
true, but more adherent to the tissues, and less alterable by air and
light. It seems to me, also, that taste would lose nothing; and that
printed stuffs, colored in a manner less brilliant, but more
harmonious, would be perhaps more appreciated, especially by those who
use them.”
The tendency to substitute the brilliant for the stable dyes prevails
too much in our own manufacture. A very considerable cloth
manufacturer replied to our inquiry as to the extent to which he used
indigo: “I hardly use it at all; the dye of the indigo blue is not
bright enough to be popular.” On the other hand, we have heard our
leading manufacturer of carpets, whose cultivated taste has led him to
partake of M. de Kæppelin’s views, deplore the introduction of aniline
dyes, as a positive calamity to the textile industry. It is the
influence of the trade, the immediate consumers of fabrics, rather
than the judgment of manufacturers, which promotes the use of the
modern fugacious dyes. The dealers desire not only to imitate the
fashionable colors of European goods, but to secure the utmost
cheapness. One of our largest manufacturers of woollen goods, who had
made a special study of the best processes abroad, and was desirous of
bringing better dyed goods into more general consumption, urged one of
his largest customers, an extensive dealer, to allow him to dye the
waterproof cloakings which he was furnishing for his house, in fast
indigo colors, assuring him that he would charge simply the additional
cost of the indigo, without profit. The offer, which involved the cost
of only a few cents a yard, which would have been gladly paid by the
last consumer if the difference of value had been made known, was
declined. It is not improbable that the inferior goods which the
manufacturer was compelled to furnish were sold to the public as fast
dyed. Our manufacturers, therefore, may not have been responsible for
the predicament in which the most enthusiastic defender of our
protective policy found himself, as we have it from his own lips.
Being about to make a speech in Congress in defence of American
industries, he put on, for the first time, a coat declared to have
been made of American cloth. Sitting down, heated and perspiring from
the excitement of his effort, he found that beneath the arms whose
gestures had enforced his eulogies of American industry, the pretended
fast blue of his coat had become _red_, literally _blushing_ for its
unmerited praise. That fast-dyed goods of the highest excellence can
be and are furnished by American manufacturers, is shown by our army
cloths. The government specifications, copies of which are published
elsewhere in this number, require that all the blue woollen cloth, cap
cloth, and flannels furnished for the army shall be “pure indigo
dyed.” The requisition is strictly enforced. The admirable effect of
this regulation may be witnessed at any dress parade of a battalion of
United States soldiers. The persistency and uniformity of the hue
under constant wear—the cloth of the common soldier in its superior
dye often favorably contrasting with the finer but fancy dyed cloth of
the officer—is one of the circumstances which justify the assertion,
that our army is the best clothed in the world. The contrast is more
remarkable still with the _quondam_ blue cloth, converted by sun and
rain-into every shade of shabbiness, which we purchased in Europe for
our soldiers at the commencement of our late war.
ORIGIN AND EXTRACTION OF INDIGO.
Indigo is a coloring material of vegetable origin, which owes its
color and its important applications to a direct blue principle, known
under the name of indigotine. It has been used as a dyestuff from time
immemorial, by the inhabitants of India; and it is from the East, the
cradle of the textile arts, that Europe has derived it. It was
probably received from India by the Greeks, among other products first
made known to them by the expeditions of Alexander the Great.
Dioscorides clearly refers to indigo in mentioning the two coloring
matters brought from India. Pliny mentions a coloring material, having
an admirable mixture of blue and purple, as coming from India, which
he calls _indicum_. That he refers to indigo is curiously manifest by
the test which he gives, by which the genuine drug might always and
_certainly be distinguished from the spurious_. This is by putting it
on live coals, when, says he, “the true _indicum_ will burn with a
flame of a most beautiful purple tint.” The purple vapor from burning
indigo is still a characteristic test. The Romans, it is apparent,
used indigo only as a pigment, not knowing what is still the most
important art connected with its use,—how to make it soluble so as to
be available in dyeing.
That indigo as a commercial product was first obtained from India is
not only proved by the testimony of Pliny, and other ancient writers,
but is confirmed by a variety of circumstances, and particularly by
its name, which is known to have been _nil_ in the Hindu language,
from the earliest times of which there is mention of it. This name is
still given by the Hindoos to the color blue, and to all the plants
producing indigo. The Arabs and Egyptians, who obtained a knowledge of
indigo from India, adopted the Hindu name, the Arabs calling it _nil_
or _nir_, and the Egyptians _nil_ or _niel_. The Portuguese preserved
the Indian name, with a slight modification, the substance being
called _aniliera_ in their language. The coloring substances
afterwards found in coal-tar having been first found in indigo, modern
science has adopted for them the name of _aniline_.
It has been asserted that this substance was not known in Europe until
the time of the discovery of the passage to India round the Cape of
Good Hope. But Dr. Bancroft has shown that indigo was brought by
merchants from India to Alexandria, and thence to Venice, when that
city was the _entrepôt_ of Europe and the East. It doubtless
contributed to the excellence which the Italian states first attained
in the wool manufacture. The drug was called _endigo_ in Venice, and
it is from that city that we have derived its name and use. It was
imperfectly known in England under its Spanish name in the sixteenth
century, for we find in Hackluyt “Voyages” his instructions to a
traveller who was going to Turkey to ascertain “if _anile_, that
coloureth blue, be a natural commodity of those parts, and if it be
composed of an herbe.”
The general introduction of indigo into Europe was impeded by
legislative enactments, prompted mainly by those employed in
industries which it threatened to displace. These were chiefly the
producers of and dealers in _woad_, formerly used exclusively for
dyeing blue, and the corporation of woad dyers. When dyers from Italy
and Flanders attempted to introduce the superior dyes of indigo, the
woad interests were sufficiently powerful to induce the Elector of
Saxony to denounce the use of the new dyestuff. It was pronounced in
the Diet of the Empire as “a corrosive color,” and “fit food only for
the devil,” _fressende teufels_. Similar propositions were made in
England and France, in which latter the free use of indigo was not
permitted until 1737.
Although indigo as known in the arts is a product of vegetable origin,
we must not omit to notice that one source of its production is the
human body. It was discovered some years since that the blue color
sometimes found in diseased urines, and in certain suppurations, is
due to indigo. Dr. Schunck, in some papers read before the Royal
Society, has shown that it is a frequent constituent of urine secreted
by persons in a healthy state, and that, in fact, it is produced
generally when persons do not take sufficient exercise; and he has
several times succeeded in producing it by taking in his food a rather
large excess of sugar. He has found this substance also in the urine
of beef cattle. It must also be observed that the chemical actions of
indigotine with oxidizing agents, showing indigo to have a very close
relation to aniline and carbolic acid, both products derived from
coal-tar, have produced in the minds of chemists the conviction that
indigotine, like alizarine, the coloring principle of madder, will one
day be artificially produced from coal-tar.
The plants which are known to furnish indigo are quite numerous, being
not less than sixty; they do not all belong to the same family, and
none of them contain the coloring principle already formed. The most
important belong to the leguminous family, from which most of the
vegetable dyes are derived, and to the genus _indigofera_. The species
cultivated and most esteemed are _Indigofera tinctoria_, _I.
disperma_, _I. anil_, _I. argentea_.
[Illustration: Drawing of the Indigofera tinctoria plant]
The principal source of the indigo of commerce is the _Indigofera
tinctoria_. The accompanying figure is a correct representation of the
plant, and we may dispense with a description of its botanical
characters, observing only that the plant has a half woody stem, and
rises to the height of from three to five feet. The plants exhale a
strong odor towards evening in the fields where they are cultivated.
The leaves have a disagreeable taste, and rapidly putrefy in water.
The plant originated in Campaja, or Guzerat, but is cultivated in
Hindostan, China, Java, and in the East Indies generally. It was
carried by the Spaniards to South America and the West Indies, and it
can be acclimated in all hot countries. The _Indigofera argentea_, or
indigo plant of Egypt, furnishes the indigo produced in that country
and Arabia.
The culture of the plant and the production of commercial indigo is
carried on a vast scale in Lower Bengal. We have before us a large
map, placed at our disposal by an India merchant of Boston, showing
the location of each of the hundreds of factories of that important
centre of production. These factories have been developed by British
enterprise; and India thus receives some slight compensation for the
ruin of her cotton manufacture by the same influence.
The propagation of the indigo plant in that country is made by sowing
in a thoroughly tilled silico-argillaceous soil. The seed of the plant
is sowed annually in the spring or autumn, according to the variety
used, some germinating more slowly, and requiring to remain in the
ground longer than others. The time of putting in the seed is also
governed by the nature of the soil and its position in respect to
neighboring rivers. In the lowlands subject to inundations, the indigo
ought to be all cut at the period of the rains and inundations, which
would destroy the crop in a brief time. Besides, during the rainy
period the planter has at his disposal sufficient water to commence
his operations of fabricating the indigo, which is the suitable time
for beginning the cutting of the plant. The time of cutting the
indigo plants is therefore regulated by the elevation of the land and
danger from floods. The high lands are always sowed several weeks
after those subject to inundations.
The Chinese prick out the young plants in parallel rows, always
preserving the land quite clear of weeds. By taking away the blossoms
of the plant before their development, they increase the growth of the
leaves, and, consequently, the return of indigo; for it is in the
leaves principally that the coloring material is found.
In certain localities the planters break off the leaves which have
acquired a bluish green tint. But more frequently the whole plant is
cut down close to the ground in the months of June or July, when the
flowers begin to open. The portion of the plant which remains pushes
up quite rapidly, and furnishes a second, and even third, and
sometimes, though rarely, a fourth cutting. The quality of the product
diminishes according to the number of the cuttings.
The plant called _nil_, cut down to the root and gathered up in
packages, is worked up the same evening. The package is formed from
the product of a space of land embraced by a chain about three yards
long. The value of the first material changes with the value of the
soil. Thus, one soil produces a plant which has many stems and few
leaves, while another gives many leaves and few stems. The richness in
coloring material depends upon the quantity of leaves, but varies also
with an equal weight of leaves with atmospheric influences. Thus
regular dealers in the article observe a marked difference in the
quality of indigo in different seasons.
M. A. Koechlin Schwartz has recently published some interesting notes
upon the preparation of indigo in Lower Bengal. In that country, which
furnishes excellent indigo, the factory includes, besides filters,
presses, a steam-engine, drying apparatus, and reservoir of water, two
lines of vats, arranged one above the other, from fifteen to twenty in
each line. These vats are built up with bricks, and covered with a
strong coat of solid and well made stucco. They are square, about six
yards on a side, and about a yard deep. The back row is about a yard
above the front one. The plant is fermented in the vats of the upper
row; when the operation of fermentation is terminated, a faucet is
opened, and the liquid is run into the lower vat. The water of the
Ganges, which is relatively pure, and thus well suited for this work,
is brought into basins of deposition, where it becomes clarified, and
is distributed by a common canal to the vats of the upper row. The
plants, cut in the morning and bound up into packages, come to the
factory after midday, and are thrown into the vat in the evening. A
vat contains one hundred packages carefully arranged, one beside the
other; heavy timbers are placed upon the plants, which are pressed
down by means of large wedges. It is necessary that the plants should
be pressed together very compactly, as without this the fermentation
does not take place to advantage. At nightfall the water is introduced
into the vats, and fills them so as completely to submerge the plants.
The fermentation is more or less prolonged according to the
temperature. Its duration varies from nine to fourteen hours. The
workmen judge as to the procedure of the operation by withdrawing a
little of the liquid in the lower vat. If it is of a clear pale yellow
when withdrawn, it will furnish a product less abundant but more pure
than if of a deep gold color.
At the moment of its issue from the fermenting vat the liquid is of a
yellow color, more or less deep. The liquid is allowed to remain
undisturbed for a brief period, when twelve naked men, armed with long
bamboos, enter the vat to beat the water while it is still warm.
During this time the upper vat is emptied and cleaned out for the
succeeding operation. One vat requires seventeen workpeople (twelve
men and five women). They thrash the water for two or three hours. The
liquid passes by little and little to a pale green, and the indigo is
found on suspension in the form of small floccules. The liquor is
suffered to remain undisturbed for half an hour; it is then gradually
decanted by opening, one after the other, the discharging holes placed
at different heights. The water returns to the river, and the
precipitate, under the form of a thin _bouille_, is turned into a
reservoir. This _bouille_ is pumped up into a vessel, and made to boil
for a moment to prevent a second fermentation, which would injure the
quality of the product, by turning it black. It is suffered to rest
about twenty hours, and the next morning it is again subjected to
boiling, the ebullition being kept up three or four hours. The boiling
deposit is then turned off upon a large filter, through which the
water drips. This filter is composed of a vat constructed of masonry,
covered with stucco, about eighteen feet long by six feet wide and
three feet deep. This is covered with bamboos, upon which is a grating
of smaller reeds, and above by a stout strained cloth. There remains
upon the cloth a thick paste, of a deep blue and nearly black color.
The water which is run into the vat deposits some indigo which has
pressed through the filter. This is decanted after being allowed to
rest, and the turbid liquid is boiled the next day with the fresh
indigo.
The paste of the filter is introduced into some small boxes of wood,
pierced with holes, and provided above and below with a strong cotton
cloth. The whole is again covered with a piece of stuff, and then with
a covering of wood, pierced with small holes, and it is placed under a
press, the force being gradually applied, so as to cause the water to
run out as much as possible. There is withdrawn from the box a cake of
the size of a cake of Marseilles soap. The water squeezed out flows
back into the filtering vat, to be boiled again with the fresh indigo.
The drying of the cakes ought to be done very slowly.
The dry-house is a large building of masonry, quite high, and pierced
with many openings, provided with narrow blinds, to prevent the direct
light of the sun from penetrating into the interior. Care is taken
also to surround the dry-house with large shade-trees. The cakes take
from three to four days to dry, after which they are packed in small
boxes and carried to Calcutta, the great market of Bengal.
The details above given apply to the factories managed by European
planters. The natives operate in nearly the same manner, but with less
care, and consequently their products are inferior. The average
product of indigo in Lower Bengal is stated at 4,000,000 kilograms, or
8,840,000 pounds per year. The most remarkable fact to be noticed in
these operations is, that the blue principle is developed by chemical
action from certain absolutely colorless principles existing in the
plant. The theory of the change effected is still somewhat in doubt,
because no chemist has studied the fresh plant, and observed upon the
spot the phases of the operation of the production of indigo on a
large scale. But the most accepted theory is that derived from the
researches of Dr. Schunck, upon the _isatis_ or woad-plant, which
produces indigotine in a much less degree than the true indigo plants;
viz., that the indigo exists in the plants combined with sugar,
forming a glucoside, to which he gives the name _indican_. This
compound, under the influence of fermentation in the manufacturing
process, is supposed to be unfolded into indigo and sugar.
Without dwelling upon this question, which is beyond our province, we
observe that the plants of the genus _indigofera_ are used for the
production of commercial indigo, on account of the greater richness in
the coloring principle. Other plants, which furnish the same coloring
principle, indigotine, are more frequently used directly in dyeing to
furnish the blue principle than they are for the production of indigo.
The most important of these plants, although there are others, such as
the _Polygonum tinctorium_ and the _Nerium tinctorium_, is the _Isatis
tinctoria_, which produces pastel, or woad. This, plant belongs to the
family of cruciferæ, and is a biennial. It is represented in the
accompanying figure.
[Illustration: Drawing of the Isatis tinctoria plant]
The leaves which surround the stem are collected in May or June of the
second year, when they begin to turn yellow. The wasted and dried
leaves are sometimes used directly for dyeing, but more generally the
leaves, after being cut and dried, are carried to a mill, and then
ground to a paste, after which it is formed into a mass or heap, and
being covered to protect it from rain, is left to undergo a partial
fermentation for about a fortnight. The heap is then well mixed and
formed into balls, which are exposed to the sun and wind to dry, and
thereby prevent the putrefaction which would otherwise take place.
Being afterwards collected in heaps, these balls again ferment, become
hot, and emit the odor of ammonia, which Hume tells us, in the History
of England, gave such offence to Queen Elizabeth that she issued an
edict to prohibit the cultivation of this plant. After the heat has
continued for some time, these balls fall into a dry powder, in which
form the woad is usually sold to the dyer. The best French woad comes
from Provence, Languedoc, and Normandy. In Germany, the pastel of
Thuringia is used almost exclusively; the packages have the trade-mark
of three towers, with the numbers 4, 5. In this country, owing
probably to the prejudices of practical dyers, who have generally come
from England, the Lancashire woad is almost exclusively used. The very
little imported of late years, ranging from two thousand to twelve
thousand dollars annually in value, is used for mixing with indigo in
the so-called woad vat, to be hereafter described.
COMMERCIAL INDIGOES.
The following description of the indigoes of commerce is taken
principally from Schutzenberger’s excellent treatise on coloring
materials. It coincides very nearly with that given by Napier from
Dumas and Chevrueil. Indigoes are classed, according to their origin,
into three groups.
1. Indigoes of Asia (from Bengal, Oude or Coromandel, Manilla, Madras,
and Java).
2. Indigoes of Africa (Egypt, Island of France, Senegal).
3. Indigoes of America (Guatemala, Caraccas, Mexico, Brazil, and the
West Indies).
The three varieties in most esteem are those of Bengal, Java, and
Guatemala.
_Indigoes of Java_.—These are distinguished by the great purity of
their coloring material. They contain the minimum of extractive
organic matter. If, in spite of this, they do not give a high yield of
indigotine; this is owing to a mixture of silicious mineral substances
with their paste. The paste is soft. It adheres strongly to the
tongue, and its density is feeble. They are generally of a pure blue,
light or ash colored in the kinds which are less rich, and of a
magnificent violet blue in the superior qualities. The last take a
beautiful copper color when scratched by the nail. They are placed in
the very first rank among all indigoes in respect to fineness and
beauty, if not in richness in the blue coloring principle. Their
purity, complete absence from carbonate of lime, and the small
quantity of foreign organic materials which they contain, cause them
to be much sought for, for the preparation of _carmine_ of indigo. The
consumption of the Javan indigoes in this country is so small as not
to be appreciated.
_Bengal Indigoes_.—These are the indigoes _par excellence_, for in
them are found the most varied qualities, from the most beautiful and
rich to the most ordinary. The superior qualities are of a deep violet
blue, with a fine and uniform paste; they adhere to the tongue, are
easily pulverized, and take a beautiful coppery tint when scratched by
the nail. The fresh fracture shows a magnificent purplish blue
reflection. Their yield in indigotine does not surpass seventy-two per
cent.
After these come the reddish-violet indigoes with a purplish hue, and
a fracture more uniform and shiny. They are also more dense and hard
than the superior qualities. The reddish hue does not proceed from the
greater or less amount of coloring material contained, but from the
presence of a greater quantity of brown and red extractive matter.
These qualities are not to be despised, for the kinds which give the
best results in the dyeing vat are found in these indigoes. It would
seem, in fact, says the author whom we are following, “that the browns
and reds of indigo play an important part in vat dyeing, that they are
able to become dissolved and to fix themselves upon the tissues at the
same time as the indigotine, and thus operate to reinforce the hue.
The fact is, that dyers generally prefer the reddish indigoes to the
other varieties.” Among the Bengal indigoes there is found a clear
blue variety, less rich in coloring matter, but also more exempt from
organic substances. The impurity is constituted by mineral matters. It
is less dense, adheres strongly to the tongue, and does not take a
coppery hue, like the other varieties, when scratched by the nail.
The worst qualities of the Bengal indigoes, as in all the species, are
the clear blues, shading on to gray or green. This coloration denotes
a great quantity of extractive matter different from the indigo brown
which characterizes the red varieties, and completely inert. These
indigoes are hard, dense, adhere little or none to the tongue, and do
not show coppery reflections when scratched.
The most skilful connoisseurs distinguish forty-three varieties of
Bengal indigo. The most important are the following:—
1. _Superfine blue, light or floating_.—Color bright blue; light,
friable, and spongy; adherent to the tongue, soft to the touch,
showing coppery reflections when rubbed by the nail; paste uniform and
pure.
2. _Fine blue_.—Like the preceding, but the color a little less vivid.
3. _Violet blue_.—A little less light and friable. Has a violet blue.
4. _Superfine violet_.
5. _Superfine purple_.
6. _Fine violet_.
7. _Good violet_.
8. _Red violet_.
9. _Ordinary violet_.
10. _Good soft red_.
11. _Good red_.
12. The indigoes, _fine coppery, good coppery, ordinary coppery, and
low coppery_.
_The Indigoes of Oude and Coromandel_.—These are made in the interior
of Hindostan. Those of the best quality correspond to the middling
Bengal indigoes, and are met with in square masses, having an even
fracture, but are more difficult to break; the inferior qualities are
heavy, of a sandy feel, having a blue color, bordering on green or
gray, or even black; often in large squares, and covered with a slight
crust or rind of a greenish color. They are the most difficult to
break of all the indigoes of commerce.
_Madras Indigoes_.—They have a grained fracture, and are of a cubical
figure. The superior qualities have no rind. The qualities are fine
blue, mixed violet blue, and ordinary. They are all lighter, and less
rich in coloring matter than the Bengal indigoes.
_Manilla Indigoes_.—These occur in cubical blocks, flat squares, or in
irregular pieces. They are light, with a fine paste, and of a clear
blue. They effervesce with acids, showing the presence of carbonate of
lime incorporated in their paste. They are consequently poor in
coloring material, and are hence almost exclusively used as a bluing
material in washing fabrics.
_American Indigoes_. _Guatemala_.—These indigoes are produced now
altogether in Hunduras, although they still retain in commerce the
name of Guatemalan. They are generally found in small pieces,
irregular in form and size, and come in envelopes of skin containing
about half as much as the Bengal chests. Putting aside the difference
in exterior form, these indigoes approach very closely to those of
Bengal. The same qualities are found, only they are more frequently
mixed. The clear blue is more rare, and, when it is found, it is
poorer in coloring matter. In purchasing these indigoes it is
necessary to beware of the reds, which often contain a strong
proportion of the brown extractive matter. It is not rare to find
among the Guatemalan indigoes beautiful specimens of the blue violet,
equal to the richest Bengal variety. Unfortunately, this superior
variety is generally mixed with inferior kinds, as to have less value.
The American indigoes are classified as follows:—
_Guatemala floro_.—Bright blue, paste uniform, soft and light. This
variety, in Bancroft’s time, was the most esteemed of all indigoes.
_Guatemala sobresaliente_.—Less light, the paste firmer and the blue
less beautiful.
_Guatemala corte, or copper-colored_.—Paste less firm and heavier,
coppery red.
_Caraccas_.—These resemble very much the Guatemala varieties. The
qualities are designated by analogous names, but they are, in general,
less esteemed than the preceding.
_Mexican_.—They hold an intermediary rank between the Caraccas and
Mexican.
_Brazil_.—These indigoes are in small rectangular parallele-piped
masses, or in irregular lumps of a greenish gray color externally, and
having a smooth fracture, a firm consistency, and a copper-colored
tint of greater or less brilliancy.
_The indigoes of Africa and Egypt_.—These have only been manufactured
within the last twenty years; they are in flat squares. The paste is
fine and quite light, and the color pure blue or bordering on violet.
The varieties are distinguished as fine blue and good violet and red.
_Indigoes of the Isle of France and Senegal_. Rare in commerce, but
of good quality.
The indigoes of the inferior qualities, characterized by a salt-like
color, bordering more or less upon green; by a coarse, uneven, and
very dense paste; by not adhering to the tongue, and by not showing a
coppery color when scratched,—can never be employed to advantage,
notwithstanding their low price. The purchaser of these qualities must
be guided solely by the results of analysis; for an article is found
in commerce whose richness in indigotine does not exceed twelve to
fourteen per cent. The presence of so high a proportion of foreign
matter prevents the chemical change which the indigo ought to undergo
in the dyeing vat; and this foreign matter, added to the deposits of
the dyeing vats, causes great loss of the coloring matter. These
indigoes should be used as little as possible, especially in the cold
vats used for dyeing cotton and linen. The middle varieties of the
Bengal and Guatemala indigoes, and, above all, the red varieties,
produce in the cold vats the most advantageous results. The lower
qualities above spoken of present less inconvenience in the hot vats
used for dyeing wool; and it is for this purpose that they are
generally used. In considering the previous observations, the wool
manufacturer may arrive at this conclusion: that while he can, with
less loss than the maker of cotton fabrics, make use of the lowest
qualities of indigo, he will obtain _the best results from the middle
qualities of the reddish Bengal indigoes_.
The skilled dealers in indigo recognize not only the above
distinctions, founded upon the country of production, color, and
physical qualities, but they observe whether the article has any of
the following defects, which are designated by certain well-understood
terms: such as whether the indigo is _sandy_,—when brilliant points
are observed in the interior, which are in reality particles of sand;
_spotted_, that is to say, of unequal tint, and marked by small
blackish points; _ribboned_, marked by transversal bands of a paler,
and sometimes red color; _burnt_, the pieces having a scorched
appearance, due to rapid drying, and separating into small black
fragments under the pressure of the hand; _crumbly_, when in pieces of
irregular figure, proceeding from fractures of the squares; _cold_,
when the indigo does not adhere to the tongue. The above
classification is presented with a full knowledge that these
distinctions are by no means recognized in the ordinary commerce in
this article. It is not, however, without interest as an illustration
of the minute attention given to this subject in Europe, where a
higher manufacture requires a nicer investigation of the qualities of
materials employed.
DETERMINATION OF THE RICHNESS AND PURITY OF INDIGOES.
It is evident that the commercial form and the high price of this drug
favor fraud, and the desire to illicitly introduce foreign substances
into the paste. It is important, therefore, that the purchaser should
carefully ascertain the actual value of the article which he is to
use. He should know not only the proportion of indigotine contained,
which varies in the commercial indigoes from twelve to seventy-five
per cent, but the hardness and density. A good indigo ought to have
qualities which can be recognized by the eye and touch alone. The
first and the only examination ordinarily made by purchasers is in
respect to the physical qualities of the article. Different pieces are
selected, and their fresh fracture is attentively observed. The
purchaser observes whether the squares are like each other, and if the
parts of the same piece present the same tint. He determines the
porosity by the simple means of applying his tongue to the fresh
fracture. The more rapid the adherence of the tongue, the more porous
the indigo. By scratching the piece with his finger-nail, he
determines the extent of the coppery reflection,—an important test.
From all these characters, taken together, the purchaser can form
quite a correct idea of the value of indigoes in general; and the
greater number of dyers, both in Europe and this country, are
satisfied to make their purchases with only this physical examination.
The most experienced dealers in this country make no other examination
than the physical one. An eminent indigo broker in Boston has
permitted me to copy the following memoranda for the physical
examination of indigo from his notebook.
The chief signs of good indigo are its lightness, feeling dry when
touched, and, when broken, appearing of a beautiful violet blue. Good
indigo swims in water; if thrown upon burning coals it emits a
violet-colored smoke, and leaves but little ashes.
In selecting indigo the large regularly formed cakes should be
preferred,—those of a fine, rich blue color, extremely free from the
white adhesive mould[1], and of a clean, neat shape. When broken, it
should be of a bright purple cast, of a close and compact texture,
free from specks or sand, and when rubbed with the nail should have a
beautiful shiny coppery appearance; when burnt in a candle it should
fly like dust; that which is heavy and dull colored should be
rejected. Indigo is estimated and classed in commercial language, as
follows: fine blue, ordinary blue, fine purple, inferior purple, and
violet, strong copper, and ordinary copper. It is purchased by the
factory maund (74⅔ lbs. The Bazaar maund is 82²⁄₅₀ lbs.), packed in
cases containing on an average 2¼ cwt., dammered (pitched) and covered
with gunny bagging.
-------------------------------------------------------------
[1] Many experienced purchasers in this country pay no regard to
this mould, as it weighs scarcely any thing.—Ed.
-------------------------------------------------------------
Still, in making large purchases, as a measure of wise precaution the
chemical test should be added. This is used to ascertain the
proportion per cent of indigotine which a given indigo has. The
determination of the quality of indigotine contained is not alone
sufficient to fix the value of an indigo. With an equal yield of
indigotine, the indigoes are always to be preferred which have a light
and soft paste; and for the preparation of the indigo vat the
preference should be always given to the violet red rather than to the
clear blue indigoes.
The chemical works which treat of this subject give elaborate details
of a great number of processes for determining by chemical tests the
amount of indigotine, or the coloring material in indigoes. To give
these numerous processes would only confuse the reader. In our own
confusion upon this subject we submitted the descriptions of these
various processes to one of the most eminent and practical of American
chemists, Dr. Charles T. Jackson, an official State Assayer for the
State of Massachusetts, who has had much experience in testing indigo,
with a request that he would describe the process which he approves
and practises. He has obliged us by the following communication:—
Boston, Nov. 21, 1872.
No. 47 Court Street, Room 4.
John L. Hayes, Esq.
Dear Sir,—In reply to your inquiry as to the simplest method of
analyzing indigo, I would say that I first ascertain the amount per
cent of earthy matters and metallic oxides, in the samples brought to
me, by burning a weighed quantity in a counterpoised platinum
crucible, until all organic matters are removed or consumed, and then
weighing the ashes obtained. The ash is then subjected to analysis in
the usual way, and lime, alumina, peroxide of iron, and some other
earthy impurities are separated.
Then, to determine the amount of coloring matter, or indigotine, I
make use of a standard sample of pure reduced indigo, which is
dissolved in the most concentrated sulphuric acid, and diluted with
water after solution. Then I ascertain how much bleaching powder
(chloride of lime) is required to dissolve the solution. This is the
quantity required for absolutely pure indigo.
Now, the indigo of commerce does not contain more than say from forty
or fifty per cent of pure indigotine, and of course will require a
smaller quantity of bleaching powder to decolor it; or the quantity of
bleaching powder to decolor a given weight of pure indigo may be
weighed out, and the sample to be compared having been dissolved in
strong sulphuric acid, and diluted with water, is to be poured in and
stirred or shaken well until the point of decoloration is ascertained.
In this case it is best to weigh out at least twice as much of the
sample to be tested as was used of pure indigo, and to measure the
solution in a graduated glass vessel,—an alkalimeter, for example,—so
that by measure we may know exactly how much of the sample we add to
the solution of bleaching powder. Thus the relative coloring values of
the samples may be readily ascertained.
If you have no purified indigo on hand, you can make a good
comparative trial of your samples against a perfectly good sample of
Bengal indigo, which may be kept for a standard of comparison. Very
useful practical results may thus be obtained.
It is well, however, to keep on hand a standard sample of pure indigo,
prepared from reduced or white indigo, as directed by Berzelius (vol.
vi. page 3, French ed., 1832), and in Muspratt’s Chemistry applied to
the Arts (Dyeing, Indigo).
In the analysis by reduction of indigo, the process is simply as
follows: Reduce the indigo to fine powder, and weigh it; weigh out an
equal quantity of pure quicklime (made from pure white marble).
Measure in a graduated vessel a certain volume of water. Slack the
lime with a portion of this water. The rest of this water is to be
used in rubbing up the indigo in a mortar. Then the slacked lime is to
be mixed with the indigo, rubbing the substances well together.
Introduce the whole into a large flask; 1½ to 2 litres (about 3 to 4½
pints) of water is required for 1 gramme (or about 15 grains of
indigo). The flask and contents are then to be exposed to a heat of
from 176° to 190° F. for some hours. This is best effected in a water
bath. By this digestion the lime is made to combine with the indigo
brown, and the coloring matter is set at liberty. Dissolve in the
liquor a little protosulphate of iron, exempt from copper, and reduced
to a fine powder. The flask is to be corked and well shaken, and
allowed to cool. When the sediment is settled, decant the clear
solution by means of a syphon into a graduated glass. The coloring
matter oxidizes by exposure to the air; and to favor this oxidation
and to keep the lime in solution, add muriatic acid to the liquor.
When the liquor has become clear, filter and collect the precipitate
on a weighed filter, which wash with hot water, and dry at a
temperature of 212° F. Thus we can learn, by weighing the filter
again, how much indigotine is contained in the sample.
If we make use of 200 measures of water, and have drawn off 50
measures of the solution to oxidate, and this 50 measures has produced
10 grains of indigo, the whole sample evidently contained 40 grains of
indigo blue.
This method serves both for an assay of the sample and the production
of a standard sample of pure indigotine. The operation may be carried
on upon a larger scale for the manufacture of a standard sample.
Yours truly,
C. T. Jackson.
Dr. Jackson adds the following note:—
In the processes given I have not referred to the qualitative analysis
or testing for all the kinds of adulterations, but have given only
valuation of the coloring power of indigo.
I have had occasion to search indigo for Prussian blue, an occasional
adulterant. This is ascertained by caustic potash, which becomes in
part an oxide if Prussian blue is present. This acidulates with
muriatic acid, and, tested with sulphate of iron, proves, by formation
of Prussian blue, the presence of the ferrocyanide of potash in the
solution, and hence Prussian blue in the indigo. Lime and clay are the
usual adulterants, and oxide of iron is often present accidentally or
from the clay adulterants. Starch and flour are rarely used, as they
add little to the weight.
C. T. J.
COMMERCE IN INDIGO.
Before proceeding to a consideration of the practical applications of
indigo in manufacturing, we must pause to make some general
observations upon the commerce in indigo.
The first European impulse given to this commerce was made by the
Spanish and Portuguese. They not only imported indigo from the Indies,
but established its fabrication in their colonies. To them we owe its
production in Guatemala, Caraccas, and Brazil. The French exported
from the Island of San Domingo, only, in 1774, 2,350,000 pounds weight
of this commodity. British influence was exerted in favor of the
development of this article in the American colonies, and, in 1773, in
the space of twelve months, over a million pounds of indigo were
exported from South Carolina. The production in India was at that time
of little importance. It was not until 1783 that the attention of the
English was directed to the culture of indigo in India for European
consumption, that produced by the natives being all consumed in their
own manufactures. In the hands of the English this product rapidly
rose to be the most important of India, in a commercial view, except
that of rice. The small cost of a factory, and the comparatively small
capital required for this production, caused the indigo culture to be
preferred to sugar planting. The importation and sale of this
commodity at the East India House, in 1792, amounted to 581,827 lbs.,
while the importation into Great Britain from other parts of the world
amounted to 1,285,927 lbs. In 1806 the importation from the East
Indies, and sales at the East India House, amounted to 4,811,700 lbs.,
and produced in sterling money £1,685,275. In the year 1862–63, the
export from India, and the destination of supplies, were as follows:—
Destination. Quantity. Value.
----------------------------------------------------
United Kingdom 8,537,133 lbs. $1,627,035
America 134,064 26,949
Arabian and Persian Gulfs 343,037 33,385
France 1,922,120 371,396
Germany 85,680 15,504
Suez 295,269 51,730
Other places 9,577 815
----------------------------------------------------
Total 11,326,880 lbs. $2,126,814
The value of exports in 1866 was £1,861,501. In the same year the
imports of indigo from the whole of Central America, including
Honduras, was 672,480 lbs. The consumption of indigo in Great Britain
did not increase during the ten years ending with 1867. This
stationary demand, notwithstanding the fall in the price of the drug
and increase of population, is attributed by McCulloch principally to
the decreasing use of blue cloth. It is more probably due to the
substitution of cheaper dyes. The average home consumption in Great
Britain for seven years ending in 1867, was 1,675,072 lbs. per year.
The importation into this country for the twenty years last past is
shown by the following table, kindly prepared at our request by the
chief of the Bureau of Statistics:—
_Statement of Imports of Indigo into the United States during the
Fiscal Years ended June 30, 1853–1872._
INDIGO.
Fiscal
Year
ended
June 30 FREE OF DUTY. DUTIABLE.
--------------------------------------------------
Pounds. Dollars. Pounds. Dollars.
1853 1,387,847 947,367
1854 1,965,789 1,282,367
1855 2,097,397 1,151,516
1856 1,732,290 1,063,743
1857 1,533,037 1,010,509
1858 1,647,767 945,083
1859 1,773,868 1,441,429
1860 1,707,116 1,413,790
1861 185,039 160,138 719,563 505,766
1862 2,501,052 3,281,441
1863 885,834 1,008,187 178,364 219,169
1864 684,813 623,406 897,821 671,899
1865 741,438 601,283 415,575 324,207
1866 798,855 609,160 44,660 41,268
1867 1,069,506 816,974
1868 870,164 775,751
1869 1,574,449 1,649,550
1870 1,270,579 1,203,664
1871 1,994,172 2,052,222
1872 1,526,869 1,484,744
EDWARD YOUNG, _Chief of Bureau_.
Bureau of Statistics, Nov. 16, 1872.
The extraordinary quantity imported in 1862, we hardly need remark,
was due to the demand for consumption in army cloths. Indigo imported
directly, was made free of duty in 1861. The duty which appears by the
above table to have been charged since that period, was upon indigo,
the product of India, imported by way of England, which was subject to
an extra duty of ten per cent.
The indigo consumed in the United States is generally supplied by the
Boston and New York Calcutta houses, who have either an American
partner resident in Calcutta, or who employ a resident American as
agent. Indigo, like other Calcutta goods, is sold through the agency
of brokers, who receive on this article a commission of one per cent.
The value of the article is known almost daily in these cities by
telegrams, giving exact information of the state of the trade,
transmitted from Calcutta as often as every five days. Some of the
brokers publish monthly circulars, showing the stock of indigo with
other Calcutta goods on hand in our market. The regular trade reports
issued by the India merchants show that The higher qualities of indigo
do not come to our market. The following is an extract from a report
of Whitney, Brother, & Co., of 1871:—
Indigo for Continent fine 350 to 362 rupees.
„ „ „ good 330 „ 345 „
„ „ „ middling 310 „ 325 „
American consuming fine 280 „ 300 „
„ „ good 250 „ 275 „
„ „ middling 200 „ 240 „
„ „ low and ordinary 150 „ 170 „
At the present moment there is great depression in the trade in this
article. The last telegrams show a decline of price in the Indian
trade in this article of from fifty to seventy-five per cent from the
prices of last year; and the apprehension is even entertained that
indigo is going out of use, the dreaded competitors being the aniline
dyes, and particularly the Nicholson blue. We maybe presumptuous in
giving our opinion on the question, but we hazard the prediction that,
notwithstanding the temporary popularity of the cheap substitutes, a
reaction will take place in favor of that “wonderful and most valuable
production,” whose importance as a dye has been held in India for
thousands of years and Europe for two centuries, “greatly to exceed
any other.”[2]
-------------------------------------------------------------
[2] The “Dictionnaire Universel du Commerce,” &c., published in
1861, contains an exhaustive article on the commerce in indigo,
by M. S. Beekrode. From the statements of this writer, it appears
that the consumption of indigo was estimated, in 1835, as follows:—
Great Britain 1,214,380 kilograms (2,683,779) lbs.
France 912,915 „ (2,017,542) „
United States 130,000 „ (277,300) „
Other countries 2,435,473 „ (5,382,395) „
--------- -----------
Total 4,692,768 kilograms (10,362,016) lbs.
The approximate consumption in 1859 is stated as follows:—
Great Britain 800,000 kilograms (1,768,000) lbs.
France 800,000 „ (1,768,000) „
United States 400,000 „ ( 884,000) „
Russia 860,000 „ (1,900,600) „
The Zollverein 1,250,000 „ (2,762,500) „
Switzerland 150,000 „ ( 331,500) „
Austria 400,000 „ ( 884,000) „
Other countries 300,000 „ ( 663,000) „
--------- -----------
Total 4,960,000 kilograms(10,961,600) lbs.
The average production in 1859 is estimated as follows:—
Bengal, Madras, &c. 3,500,000 kilograms (7,735,000) lbs.
Java 550,000 „ (1,215,500) „
Central America 300,000 „ ( 663,000) „
Other sources 100,000 „ ( 221,000) „
--------- -----------
Total 4,450,000 kilograms (9,834,500) lbs.
As the maximum annual consumption in 1859 is set down at
5,000,000 kilograms, the author concludes that the average
production at that time did not surpass the requirements of the
dyers of the whole world.
-------------------------------------------------------------
FORMER PRODUCTION IN THE CAROLINAS.
As pertinent to the commercial branch of our subject, we must briefly
notice the remarkable facts of the sudden growth and equally sudden
and extraordinary extinction of the production of indigo in the
Carolinas. Indigo was for many years the second great staple of South
Carolina. So highly was this staple estimated that the historian of
the State declares that “it proved more really beneficial to Carolina
than the mines of Mexico or Peru are or ever have been to Old or New
Spain.” Its introduction was the happy result of a woman’s culture and
energy. In the early part of the last century, the indigo plant had
been extensively cultivated in the West India Islands, which then
furnished the chief supply of Europe. The governor of Antigua, George
Lucas, whose home plantation was at Wappoo in Carolina, having
observed the fondness of his daughter, Miss Eliza Lucas, afterwards
the mother of General Charles Cotesworth Pinckney, for the culture of
plants, was in the habit of sending to her tropical seeds to be sowed
on his plantation at Wappoo. Among others, he sent her some seeds of
the indigo plant cultivated in the West Indies. She planted them for
two years; but the seeds failed to germinate, or were killed by the
frost. On the third year’s trial, in 1741 or 1742, she was successful.
Governor Lucas, on hearing that the plants had ripened and produced
seed, sent from Montserrat a person skilled in making indigo. Vats
were built on Wappoo Creek, and there the first American indigo was
manufactured. The attempts of the expert to conceal his processes were
defeated by the vigilance of Miss Lucas. The process of manufacture
was made known. Seeds from the Wappoo plantation were freely
distributed and successfully planted; and the culture of indigo became
common. In 1747, a considerable quantity of indigo was sent to
England, which induced the merchants trading with Carolina to petition
parliament for a bounty on Carolina indigo. In 1748, an act of
parliament was passed granting a bounty of sixpence per pound on
indigo raised on British-American plantations and imported directly to
Britain from its place of growth. This act stimulated the planters of
Carolina to double vigor in the production of this new material for
export. “Many of them,” says Dr. Ramsay, “doubled their capital every
three or four years by planting indigo.” In the year 1754, the export
of indigo from the province amounted to 216,924 lbs., and in the years
1772 and 1773 the export had risen to 1,107,661 lbs. The production
was greatly checked by the war of the Revolution. Near the close of
the century the large importations from India lowered the price, so as
to make the planting unprofitable. In the mean time, the culture of
cotton had sprung up under the protective tariff of 1789. The grounds
suitable for indigo planting were equally fitted for cotton, and were
for the most planted with the new staple. It is curious to observe how
the former was displaced by the latter staple. The export of indigo
from Charleston in 1797 was 96,121 lbs.: in 1800, it fell to 3,400
lbs. During the same years, the exports of cotton rose from one
million to six and a half million pounds. The production of American
indigo appears to have revived from time to time up to 1829. A writer
of that period in Silliman’s Journal of Science estimates—although it
would seem on doubtful authority—the production of indigo in the
United States at 20,000 lbs. The price of the American article had
fallen, owing to the great quantity of extractive which it contained,
to fifty cents per pound, while the Bengal indigo was worth $1.15 per
pound. We have no data as to its production at the present time, but
infer, from the fact that no reference has been made to this product
in the Government Agricultural Reports for many years past, that the
production, if any, is too unimportant to be noticed.
INDUSTRIAL APPLICATION OF INDIGO.
All the applications of indigo require that the material should first
be reduced to an impalpable powder. It is better to grind it with
water, to prevent the loss of material in the form of powder, although
the dry pulverization is necessary when the indigo is to be used for
the manufacture of the sulphate. To facilitate the grinding the
material into a paste, it should be previously soaked in hot water
from one to three hours. The grinding on a small scale may be done by
a very simple apparatus. This is a hemispherical vessel of copper or
cast-iron, eighteen inches in diameter, furnished at the edge with two
handles. The workman, sitting astride a bench, places the vessel
before him, in which he places three heavy cast-iron balls, the indigo
which has been softened, and a sufficient quantity of water. Holding
the basin by the handles, he gives it a circular oscillatory movement,
in such a manner that the balls, following this movement, crush the
indigo which surrounds them; after which the contents are poured into
another vessel, water is added, and the material is stirred. The
portions incompletely ground are made to reunite themselves at the
bottom by means of regular blows with a hammer on the rim of the
vessel. The upper liquid is decanted, and the deposit is submitted to
a new manipulation in the basin.
In large establishments the grinding is done by machinery. An
apparatus highly recommended, consists of two circular plates of
cast-iron, arranged horizontally and slightly separated, one from the
other, which are rapidly rotated by power, in inverse, directions. The
interior surfaces of these disks are provided with deep grooves
radiating in a curved line from the centre to the circumference, and
diminishing in depth in the same direction. The indigo which has been
previously softened enters between the two plates by an opening in the
centre of the upper one, and escapes in a thin paste by the
circumference.
The application of indigo to the coloring of textile fabrics requires
the complete dissolving of the substance, for which the mechanical
division is only a preliminary. There are only two known means of
dissolving this substance: 1. By reduction; 2. By the action of
concentrated sulphuric acid. The first means allows indigotine to be
regenerated; and, when the dyeing is completed, it is pure indigotine
which adheres to the colored fibre. By the second means, or dissolving
by sulphuric acid, the coloring material enters into a new
combination, from which it can never be separated: it becomes a new
substance, endowed with new and special properties.
_The fixing of Indigotine by means of Reduction_.—In this method the
operator avails himself of one of the most remarkable qualities of
indigotine: this is the facility with which this body takes up
hydrogen, and becomes transformed into a colorless substance, which is
soluble in favor of alkaline or alkaline-earthy bases, and is
susceptible of reproducing indigotine by simple oxidation in contact
with air. This hydrogenized substance is called white indigo. Blue
indigo, or indigotine, is insoluble except by concentrated sulphuric
acid; and this insolubility gives it its superiority to all other blue
dyes. Not being soluble, it cannot, as blue indigo, attach itself to
the material to be dyed; but in the soluble form of white indigo it
can perfectly penetrate the fibre. If by any means of oxidation we can
transform the white indigo into blue indigotine, the latter becomes
insoluble, and is imprisoned in the pores of the fibre. This is,
briefly, the whole theory of the use of indigo in dyeing or printing,
although the reaction may be applied in different ways to the coloring
of fibres, such as—
1. The indigo is dissolved by means of an alkaline reduction in a vat,
and the fibre is immersed in the bath. This is the common blue vat.
2. The solution prepared beforehand is painted by a hair pencil and
printed by a stamp or roller upon only certain parts of the tissues.
This is the pencil blue.
3. The white indigo is precipitated under the form of a paste, in
combination with a metallic oxide having strong reducing power, such
as hydrated protoxide of tin, which prevents the too rapid reoxidation
of the indigotine. The thickened paste is printed, and the tissue is
placed in an alkaline bath (lime or soda), which, displacing the oxide
of tin, forms a soluble combination of white indigo. The latter can
then penetrate the fibre, and afterwards become fixed by reoxidation.
This is the printer’s solid blue.
4. The finely ground, but not dissolved indigo, is placed upon the
tissue in such conditions that it can be dissolved and reduced in
place. This done, the fixing of the indigotine is effected by
oxidation. This is the method for China blue or _bleu faïence_.
Without dwelling upon the details of these methods, we hasten to a
consideration of the most important of all the applications of indigo:—
DYEING BY THE INDIGO VAT.
_The Copperas Vat_.—For dyeing cotton, the method of reduction found
by experience to be the most convenient and practical is founded upon
the action of the hydrate of the protoxide of iron in the presence of
lime. The hydrated protoxide of iron is obtained from sulphate of iron
(green vitriol, or copperas) with freshly burned lime. Certain
precautions should be observed in the use of these materials. The
copperas used for the preparation of these vats should be free from
sulphate of copper, because the oxide of copper which would be formed
in the vats rapidly oxidizes the reduced indigo, and causes its
precipitation in the bath. The copperas ought not to contain red oxide
of iron, nor sulphate of alumina. The coppery or oxidized vitriol may
be purified by boiling the solution with pieces of iron, which
precipitates the iron and neutralizes the oxide. The lime ought to be
pure, containing no magnesia; when slacked lime has been exposed to
the air, even for a short time, it absorbs carbonic acid, and becomes
converted into chalk. The lime, therefore, should always be newly
slacked. The ingredients, then, of a copperas vat are water, pure or
purified green vitriol, indigo ground into a homogeneous impalpable
paste, and pure and freshly slacked lime. The proportions used in
different establishments are exceedingly variable. Those which answer
for a laboratory vat, or a small vat used for precipitating the white
indigo immediately for printing, are: indigo, one part; sulphate of
iron, two parts; slacked lime, three parts. These proportions are not
enough for the large vats used in dyeing pieces. In them it is
necessary to make the quantities of lime and sulphate of iron larger
than the theory of the vat requires. The excess of lime and hydrate of
iron serve the purpose, whenever the vat is stirred, to repair the
losses of indigo caused by its oxidation from contact with the air.
Schutzenberger gives the proportions generally used by the dyers of
France, as follows:—
Indigo 1 part.
Crystallized sulphate of iron 3 „
Freshly slacked lime 3 „
Others, he says, use more lime than copperas, as in the following
proportion:—
Indigo 2 parts.
Sulphate of iron 5.5 „
Quicklime 6.5 „
M. de Kæppelin, who is especially familiar with the cotton dyeing in
Mulhouse, describes the ordinary vats for cotton dyeing as bound with
iron, and placed on the level of the ground. They hold from 3,000 to
4,000 litres (1,055 gallons) of liquid. In preparing them the dyer
fills them about three-quarters full of water, and pours in a milk of
lime, prepared with 45 kilograms (100 lbs.) of freshly slacked lime; a
fine liquid paste having been previously made from 15 kilograms (33
lbs.) ground in water. This is added to the lime in the vat by
portions, the liquid in the vat being stirred up by a rake after each
portion of the indigo paste has been added. The indigo becomes
dissolved in about twenty-four hours, when the vat can be used. After
describing the manner in which the frame, or _champignon_, containing
the goods to be dyed is arranged and immersed in the vat, this author
continues: “It will be understood that the vat is composed according
to the degree of intensity of the color which is sought to be
obtained, and that hues more or less deep may be obtained by means of
more or fewer repeated immersions of the fabric to be dyed. After each
immersion the _champignon_ is lifted out of the vat, and the fabrics
are left to _ungreen_ themselves by contact with the air. (It must be
observed that, although soluble indigo is called white, because it is
without color when carefully prepared in the laboratory, the goods,
when first taken from the ordinary vat, are of a green color.) Exposed
to the air, the soluble indigo is precipitated in the state of blue
indigo upon the fibres of the tissue. This oxidation, or
_dehydryzation_, may be hastened by plunging the tissue into a vat
containing a solution, very much diluted with water, chloride of lime,
bichromate of potash, or sulphuric acid. The first two act as
oxidizing agents; the last facilitates the restoring of the blue
indigo by depriving it of the lime which is in excess in the solution
of indigo which the tissue has imbibed from the vat.”
He adds further: “To facilitate the formation of blue indigo in the
interior of the fabrics, the stuff to be dyed may be previously
impregnated by a saline solution, which has the property of
precipitating the white indigo from the alkaline solution, and of
fixing itself more rapidly upon the tissue. Oxide of copper and oxide
of manganese possess these properties in a high degree, and are used
in many establishments to hasten the dyeing process, and produce an
economy in raw materials. The pieces of cloth are placed in a solution
of sulphate of copper, in the proportion of 15 to 20 grams to the
litre (2.11 pints), and lightly thickened with starch. The fabrics,
thus impregnated by a kind of mordant, before receiving the blue dye
are first passed through a weak bath of milk of lime, which fixes the
oxide of copper upon the tissue. The blues thus obtained are more
intense, and have a peculiar lustre. This process is used in Austria
and Germany, where cotton fabrics are printed on both sides of the
tissue.”
Coming to the English authorities, Dr. Grace Calvert, in his recent
lectures before the Society of Arts, speaking of the cold vat for
dyeing cotton, says: “The oldest, and still most generally employed
method of preparing cold vats, consists of putting into a vat
containing about 2000 gallons of water 60 lbs. of indigo, very finely
powdered, 180 lbs. of slacked lime, and 120 lbs. of sulphate of
protoxide of iron, or green vitriol (free from any trace of copper
salt), the two latter substances being added from time to time. The
greater part of the lime used unites with the sulphuric acid of the
iron salt, to produce sulphate of lime or gypsum; and the liberated
protoxide of iron removes the oxygen from the indigo, becoming
converted into saline oxide, whilst the reduced indigo dissolves in
the excess of lime employed.”
He adds the following facts, which may be of practical value:—
“Messrs. R. Schloesser & Co., of Manchester, have introduced within
the last year or two a marked improvement, in the preparation of cold
vats, which removes the great objections of the bulky precipitate of
sulphate of lime, the formation of an oxide of iron, and the loss of
indigo by its combination with the oxide of iron. The bath remaining
much more fluid, the pieces are less apt to be spotted, and a better
class of work is produced. To carry out their process, they add to the
ordinary 2,000 gallon vat 20 lbs. of ground indigo, 30 lbs. of iron
borings, 30 lbs. of _their remarkable powdered zinc_, and 35 lbs. of
quicklime; the whole is stirred up from time to time, for twenty-four
hours, when it is ready for use. If the bath is not considered
sufficiently strong, a little more lime and zinc are introduced. The
chemical theory of the process is, that the zinc, under the influence
of the lime, decomposes the water, combining with its oxygen, and the
hydrogen thus liberated removes oxygen from the indigo which then
dissolves in the lime.”
An excellent description of the processes employed at Manchester,
England, in preparing and working the copperas, or cold vat, is given
in Ure’s “Dictionary of Manufactures.” “The ingredients necessary for
setting the vat are copperas, newly slacked quicklime, and water.
Various proportions of these ingredients are employed, as, for
instance: 1 part by weight of indigo (dry), 3 parts of copperas, and 4
of lime; or, 1 of indigo, 2¹⁄₂₃ of copperas, and 3 of lime; or, 8 of
indigo, 14 of copperas, and 20 of lime; or, 1 of indigo, ¾ of
copperas, and 20 of lime; or 1 of indigo, 4 of copperas, and 1 of
lime. The sulphate of iron should be as free as possible, from red
oxide of iron, as well as sulphate of copper, which reoxidize the
reduced indigo-blue. The vat, having been filled with water to near
the top, the materials are introduced, and the whole, after being well
stirred several times, is left to stand for about twelve hours. The
chemical action which takes place is very simple. The protoxide of
iron, which is set at liberty by the lime, reduces the indigo-blue;
and the indigo, which is then dissolved by the excess of lime, forming
a solution, which, on being examined in a glass, appears perfectly
transparent and of a pure yellow color, and becomes covered, whenever
it comes in contact with the air, with a copper-colored pellicle of
regenerated indigo-blue. The sediment at the bottom of the vat
consists of sulphate of lime, peroxide of iron, and the insoluble
impurities of the indigo, such as indigo-brown in combination with
lime, as well as sand, clay, &c. If an excess of lime is present, a
little reduced indigo-blue will also be found in the sediment in
combination with lime. The dyeing process itself is very simple.
The vat having been allowed to settle, the goods are plunged into the
clear liquor, and, after being moved about in it for some time, are
taken out, allowed to drain, and exposed to the action of the
atmosphere. While in the liquid, the fabric attracts a portion of the
reduced indigo-blue. On now removing it from the liquid, it appears
green, but soon becomes blue on exposure to the air, in consequence of
the oxidation of the reduced indigo-blue. On again plunging it into
the vat, the deoxidizing action of the vat does not again remove the
indigo-blue which has been deposited within and around the vegetable
or animal fibre, but, on the contrary, a fresh portion of the reduced
indigo-blue is attracted, which, on removal from the liquid, is again
oxidized like the first, and the color thus becomes a shade darker. By
repeating this process several times the requisite depth of color is
attained. This effect cannot, in any case, be produced by one
immersion in the vat, however strong it may be. The beauty of the
color is increased by finally passing the goods through diluted
sulphuric or muriatic acid, which removes the adhering lime and oxide
of iron. After being used for some time, the vat should be refreshed
or fed with copperas and lime, upon which occasion the sediment must
first be stirred up, and then allowed to settle again, so as to leave
the liquor clear. The indigo-blue, however, is in course of time
gradually removed, and by degrees the vat becomes capable of dyeing
only pale shades of blue. When the color produced by it is only very
faint, it is no longer worth while using it, and the contents are then
thrown away. In dyeing cotton with indigo, it seems to be essential
that the reduced indigo-blue should be in contact with lime. If potash
or soda are used in its place, it is impossible to obtain dark shades
of blue.”
FERMENTING VATS FOR WOOL DYEING.
The application of indigo-blue to wool and woollen tissues is always
made by means of vats, which have special names; as, the pastel or
woad vat, the urine vat, German vat, molasses vat, &c. The reduction
or _hydrogenation_ of the indigo-blue is the result of a peculiar
fermentation, which is developed within an alkaline liquor by means of
nitrogenized substances and bodies rich in sugar or hydrocarbonized
substances. It is known that in these conditions, especially where the
temperature is slightly raised, the sugar is converted into butyric
acid, and at the same time carbonic acid and hydrogen are set free. We
find here the source of the nascent hydrogen which fixes itself upon
the indigo-blue, and transforms it into white indigo, which is soluble
in the alkalies of the vat. It has recently been observed that the
butyric fermentation proceeds from the development of minute
infusoria. These animalculæ live without any supply of oxygen, and, in
fact, are killed in its presence. They therefore live at their ease in
the vat of reduced indigo, where no oxygen is permitted to enter.
The ingredients most usually employed for furnishing the
hydrocarbonaceous substances for fermentation are bran and ground
madder, although molasses is sometimes used. The nitrogenized material
is found in the woad or pastel, which is often added in very large
proportions to the fermenting vats. It is observed by the chemists who
have studied this subject most carefully, that the preparation of
vats, founded upon the principle of fermentation, does not repose upon
principles so sure and constant as those of the copperas vat, and that
many unforeseen accidents interpose to disturb the work of an
inexperienced dyer. The phenomena in fermentations are often complex.
It is admitted that in these phenomena theory has not said its last
word, and that empiricism is often more fortunate than science. In
conducting the operations of the warm fermenting vat, the conceit of
the practical dyer, so often remarked upon, is not without foundation.
By practical experience and the traditions of his art he has acquired
a knowledge of the almost insensible modification in conditions which
can change or arrest the chemical reaction. It is the knowledge of the
workman, a knowledge almost instinctive, which can never be
communicated to the books, and which is most respected by those most
profoundly informed in theory.
_The Woad or Pastel Vat_.—In former times woad, already referred to,
was the only material known to the dyers of Europe for producing the
blue color of indigo. For dyeing wool, the use of woad, now abandoned
wholly in cotton dyeing, has been retained to the present day,
generally for the purpose of exciting fermentation, and without regard
to its effect in imparting color to the material to be dyed; for the
woad grown in England, and used in the dye-houses of that country,
contains no trace of coloring matter. The woad, or pastel, grown in
the warmer districts of France contains about two per cent of
indigotine, which is regarded in that country as an important addition
to the coloring material, especially for improving the tone of the
color. Various substitutes, such as rhubarb leaves, turnip and carrot
tops, and weld, have been tried, but without advantage, with the
exception, perhaps, of weld, which is still used by some dyers. Some
chemists regard the use of woad as the remnant of a prejudice; but the
better opinion is, that this material possesses peculiar
fermentiscible qualities, whose exact action science has yet to resolve.
According to Schutzenberger, the most recent and highest French
authority, the dimensions of the pastel vat are about 6½ feet in
diameter, by 9 in depth. 100 kilograms (221 lbs.) of pastel, in balls,
is placed in the vat, which is then filled with boiling water. To this
is added 10 kilograms (22 lbs.) of madder, 3 to 4 kilograms (about 6½
to 8¾ lbs.) of bran, and 4 kilograms of quicklime, which has been
slacked, and in the form of a _bouilli_. Sometimes weld is also added.
After three hours of rest, the vat is well raked, and the operation is
repeated every three hours. There is gradually developed a
characteristic ammoniacal vapor, and a blue scum, with veins of deeper
blue, forms on the surface; and the liquid, when agitated in the air,
rapidly becomes blue. These symptoms indicate the dissolution of the
indigotine of the woad; then there is added 10 kilograms (22 lbs.) of
indigo which has been previously ground in water, and the vat is
stirred. If the fermentation appears to be proceeding too actively,
which is recognized by the disengagement of gases, it is checked by
the addition of a proper dose of lime. On the other hand, the
fermentation is made more active by increasing the dose of bran. The
first dyes are not so good as those subsequently obtained, as the woad
absorbs from the bath certain brown or yellow materials, kept in
solution, and furnished as well by the pastel and madder as by the
indigo itself. 100 kilograms of wool require from 8 to 12 kilograms of
indigo. The vat is kept up by successive additions of indigo and lime,
made in the evening.
Another kind of pastel vat, prepared much like the last, receives an
addition of a dose of potash. M. de Kæppelin describes it as the one
at present in general use in France. Into a vat containing from 3,000
to 4,000 litres (791 to 1,055 gallons) there is placed 75 kilograms
(166 lbs.) of pastel in loaves, or which has undergone a kind of
fermentation; or, what is preferable, 80 to 100 kilograms (176 to 221
lbs.) of pastel or woad gathered without fermentation, and 10
kilograms (22 lbs.) of indigo, ground to a paste with water. This
mixture is well stirred, and there is added 4 kilograms (about 9 lbs.)
of Avignon madder, and the same quantity of carbonate of potash. After
the vat has been well raked there is added 2 kilograms (4½ lbs.) of
slacked lime, and some pails of bran. The vat is well covered, either
with a wooden lid, or woollen cloths. The fermentation is allowed to
proceed, and after five or six hours the vat is uncovered and raked
with much care for half an hour. This operation is repeated every
three hours, until it is recognized that the indigo is well dissolved.
In this case the bath ought to be of a beautiful yellow color, and be
covered with a light blue irised film, veined with yellow at the least
movement given to the liquid. If the fermentation proceeds too
rapidly, a little lime is added to moderate it.
For keeping up a vat like this, and to obviate the different
inconveniences to which it is subject, the dyer sometimes adds lime,
or sugar, and carbonate of ammonia, sometimes madder, or bran, or even
tartar-lees. These last additions are made to saturate the excess of
lime which the vat contains. In this case the yellow veins and the
beautiful blue scum which cover the surface disappear, or become pale;
a piquant odor is disengaged, and the liquor becomes blackish. When
lime or sugar are added, it is for the purpose of retarding the
fermentation of the woad. Sugar might even entirely take the place of
pastel for effecting the reduction of the indigo, and many
establishments in France are commencing to use it for this purpose. A
good vat, well supplied with successive additions of indigo, pastel,
bran, and madder, in proportions necessary to effect and prolong the
fermentation necessary for the dissolution of the indigo, may be kept
up many years.
Schutzenberger observes that the vats of fermentation are subject to
certain maladies, the two most frequent of which are due, one to an
excess, and the other to an insufficient quantity of lime. “In the
first case, the liquid takes a tint more and more free of color, loses
its _fleurée_ (surface scum) and odor; the fermentation is then
arrested by the precipitation of the active matters. This
inconvenience is remedied, if seen in time, by adding sulphate of
iron, which eliminates the too great excess of lime. In the second,
the fermentation becomes too active, passes into a putrid
fermentation, and the liquid assumes a reddish tint; a fabric dyed
with indigo in this state becomes very soon discolored. The sole means
of safety is to heat the bath up to 90° and to add lime. If this does
not accomplish the purpose of arresting the putrefaction the vat is
lost.”
The following account of the method of dyeing woollen goods with
indigo by means of the woad vat is given by Dr. Ure, as that carried
on in Yorkshire, the great centre of the woollen manufacture of England.
“The dye-vats employed are circular, having a diameter of six feet six
inches, and depth of seven feet, and are made of cast-iron
five-eighths of an inch in thickness. They are surrounded by
brickwork, a space of three inches in width being left between the
brickwork and the iron, for the purpose of admitting steam, by means
of which the vats are heated. The interior surface of the brickwork is
well cemented. In setting a vat the following materials are used: 5
cwt. of woad, 30 lbs. of indigo, 56 lbs. of bran, 7 lbs. of madder, 10
quarts of lime. The woad supplied to the Yorkshire dyers is grown and
prepared in Lincolnshire. It is in the form of a thick, brownish
yellow paste, having a strong ammoniacal smell. The indigo is ground
with water in the usual manner. The madder acts in promoting
fermentation, but it also serves to give a reddish tinge to the color.
The lime is prepared by putting quicklime into a basket, then dipping
it in water for an instant, lifting it out again, and then passing it
through a sieve, by which means it is reduced to a fine powder, called
by the dyers _ware_. The vat is first filled with water, which is
heated to 140° F., after which the materials are put in, and the whole
is well stirred until the woad is dissolved or diffused, and it is
then left to stand undisturbed overnight; at six o’clock the next
morning the liquor is again stirred up, and five quarts more of lime
are added; at ten o’clock five pints of lime are again thrown in, and
at twelve o’clock the heat is raised to 120° F., which temperature
must be kept up until three o’clock, when another quart of lime is
introduced. The vat is now ready for dyeing. When the process of
fermentation is proceeding in a regular manner, the liquid, though
muddy from insoluble vegetable matter in suspension, is of a yellow or
olive yellow color; its surface is covered with a blue froth or
copper-colored pellicle, and it exhales a peculiar ammoniacal odor; at
the bottom of the vat there is a mass of undissolved, matter of a
dirty yellow color. If there is an excess of lime present, the liquor
has a dark green color, and is covered with a grayish film, and, when
agitated, the bubbles which are formed agglomerate on the surface, and
are not easily broken. Cloth dyed in a liquid of this kind loses its
color on being washed. This state of the vat is remedied by the
addition of bran, and is of no serious consequence. When, on the other
hand, there is a deficiency of lime, or, in other words, when the
fermentation is too active, the liquor acquires first a drab, then a
clay-like color; when agitated, the bubbles which form on its surface
burst easily, and when stirred up from the bottom with a rake it
effervesces slightly, or _frits_, as the dyers say. If the
fermentation be not checked at this stage, putrefaction soon sets in,
the liquid begins to exhale a fetid odor, and when stirred evolves
large quantities of gas, which burns with a blue flame on the
application of a light. The indigo is now totally destroyed, and the
contents of the vat may be thrown away. No further addition of woad is
required after the introduction of the quantity taken in first setting
the vat, the fermentation being kept up by adding daily about four
pounds of bran with one quart or three quarts of lime. Indigo is also
added daily for about three or four months. The vat is then used for
the purpose of dyeing light shades, until the indigo contained in it
is quite exhausted, and its contents are then thrown away.”
This author adds: “Woollen cloth, before being dyed, is boiled in
water for one hour, then passed immediately under cold water. If it be
suffered to lie in heaps after being boiled it undergoes some change,
which renders it afterwards incapable of taking up color in the vat.
In dyeing, the cloth is placed on a net-work of rope attached to an
iron ring, which is suspended by four iron chains to a depth of about
three feet beneath the surface of the liquor. The cloth is stirred
about in the liquor by means of hooks for about twenty or thirty
minutes. It is then taken out and well wrung. It now appears green,
but, on being unfolded and exposed to the air, rapidly becomes blue.
When the vat has an excess of lime the cloth has a dark green color
when taken out. It is then passed through hot water, and dipped again
if a darker shade is required.”
_The Indian Vat_.—This presents much analogy to the woad vat, as the
fermentation of vegetable matters effects the transformation of the
indigo-blue. According to Dr. Calvert, the Indian vat, probably so
called from its origin in the East, is taking the place in England of
the old woad vat for dyeing wool and woollens. He describes its
preparation as follows: 8 lbs. of powdered indigo is added to a bath
containing 3½ lbs. of bran, 3½ lbs. of madder, and 12 lbs. of potash,
which is maintained for several hours at a temperature of 200° F. It
is then allowed to cool to 100° F., when fermentation ensues. After
about forty-eight hours the indigo is rendered soluble, being reduced
by the decomposition of the sugar and other products contained in the
bran and the madder root during the process of fermentation. The
distinguishing feature of this vat is the use of _potash_. The Indian
or potash vats are spoken of by the best authorities as more easy to
manage than the woad vat. They are less subject to accidents, and
yield their coloring material more readily to the fibre, while three
times as much wool can be dyed in the same time. On the other hand,
they do not last so long, and require to be renewed at the end of
twenty-five or thirty days. Besides, the fibres dyed in the potash vat
have a darker shade than those dyed in the woad vat, owing to the
large quantity of the coloring matter of the madder dissolved by the
potash, which becomes fixed on the stuff with the indigo-blue.
_The Urine Vat_, but little used except for domestic dyeing, is
founded upon the same principles as the other fermenting vats. This
excretion, when putrefied, contains at the same time the nitrogenized
principles which work as ferments and the alkali in the form of
ammonia necessary for dissolving the indigo.
According to Dr. Calvert, improvements have been made of late years in
the fermenting indigo vats by which the expense of madder is avoided.
They are now prepared by adding to water, at a temperature of 200° F.,
2 buckets of bran, 26 lbs. of soda crystals, 12 lbs. of indigo, and 5
lbs. of slacked lime. After five hours the bath is allowed to cool to
100° F., when fermentation ensues, and the indigo is dissolved in the
alkali. This is, in fact, the German vat, soda taking the place of the
potash, and the only fermenting material consisting of bran.
_The German Vat_ is largely used by the dyers in the north of France,
and is considered as more advantageous than the Indian vat, because
the employment of soda is more economical than that of potash, while
the vat can be maintained as long as two years. The vats used by them
are prepared as follows: The water is heated to a temperature of 95°,
and receives 20 pails of bran, 11 kilograms (about 24 lbs.) of
crystals of carbonate of soda, 5.5 kilograms (11 lbs.) of indigo, and
4½ lbs. of slacked lime. After twelve hours, the temperature having
been kept at 40° or 50°, fermentation commences, the liquid becomes of
a greenish blue color, and disengages bubbles of gas. Indigo, soda,
and lime are put in from time to time in the proportions above
indicated, and also from six to eight pounds of molasses. At the end
of the third day the vat is fit for use.
M. de Kæppelin, writing in. 1864, informs us that the reduction of
indigo by means of molasses, is at present largely employed in the
great establishments for dyeing woollen cloth at Sedan, Louviers, and
Elbœuf.
The vat used is of very large dimensions, and from twenty-two to
twenty-six pounds of indigo are dissolved in it; an equal weight of
molasses is used, and three or four times the same weight of potash
made caustic by a proportionate addition of lime.
The space reserved for this subject in our present paper will not
permit us to enter upon a description of the processes used in the
American dye-houses. This, as well as the applications of indigo in
printing, and the uses of sulphate of indigo, must be deferred to
another number.
Let us, in concluding the first part of our paper, at the risk of
repetition, bring out in bolder relief a statement which presents the
philosophy of all the various processes of the indigo vat, and at the
same time, a conclusive argument for the use of this material, in
preference to all cheaper substitutes. Indigo cannot enter into a
fibre until it is dissolved. It cannot be dissolved so long as it is
in a blue state. When reduced by any of the processes above described
to the white state, it is easily dissolved, and can enter the pores of
the fibre. Upon exposure to the oxygen of the air it takes up an
equivalent of oxygen; it returns to the blue state, and, being then
insoluble, it cannot be washed away from the fabric, and being
saturated with oxygen it cannot be changed by air or light. This
theory of the application of indigo involves a lesson to
manufacturers, dealers, and consumers, especially of woollen fabrics.
The theory, as well as experience, dating back to the dawn of the
textile arts in the East, establishes that this material is
incalculably superior to any other, in permanence at least, for
imparting to woollen fibre a blue color, or as a foundation for most
of the darker colors. By far the largest proportion of all cloths are
of dark colors,—blue, black, green, brown, gray, or mixed,—and can
advantageously receive in all or a portion of the fibre constituting
them a direct dye or bottom for other dyes from indigo. It may be
safely stated that, as a whole, no cloths in the world are
manufactured from such good wool as those produced in the United
States. We might expect that the shoddy goods of Yorkshire should be
further falsified by fugacious dyes; but is it not a shame that our
admirable wool should be deprived of half its value by parsimony in
dyeing? The slightest shortcomings in dyeing are revealed in wear. The
writer cannot forbear referring to an illustration directly before his
eyes. He is wearing a garment, reduced now to the retired service of
an office coat, made of an admirable cheviot cloth of American
manufacture. The cloth originally was selected not only for its
excellent texture, but as an illustration of philosophical principles
applied in the formation of color. The tissue was made by weaving
three yarns of distinct colors,—blue, yellow, and red. Either of those
hues alone would have been glaring and conspicuous, but, by the law of
color, the combination of blue, red, and yellow makes black, and the
new cloth at a distance had the effect of a dark mixture. Upon
exposure to ordinary wear, the yellow and red have retained their
pristine hues; the blue, not being indigo dyed, has faded; and the
original dark mixture, although sound in fabric, has become of a
yellowish brown. The extra expense of a permanent dyeing material
forms so small a proportion of the whole cost of a finished garment,
that it ought not to be generally spared. The reform cannot be made by
the manufacturers; it must be made by the dealers, and especially by
that class of producers which has risen in our day into such great
importance,—the manufacturers of ready-made clothing. If they would
demand of the manufacturers, and furnish to their customers cloths
more permanently dyed, it would be another step in the direction to
which these establishments are tending,—the supply of the chief
portion of the woollen clothing of the people. The manufacturers would
gladly aid them; for it is the growing sentiment of American
manufacturers that all their productions should be, in the proverbial
phrase adopted from the dye-house, as expressing the highest
excellence,—_true blue_.
BIBLIOGRAPHY.
Citations of authorities having been but partially made in the
preceding article, the writer, for the purpose of giving his sources
of information, and for the convenience of those who wish to pursue
the subject further, appends a list of the more important works which
he has consulted:—
Schutzenberger’s Traité des Matières Colorantes, t. ii. (the most
recent and best modern authority); Bancroft’s Philosophy of
Permanent Colors, vol. i.; Edinburgh Encyclopædia; Berzelius,
Traité de Chimie, t. vi; Chevrueil, Leçons de Chimie Appliquée à
Teinture, t. iii.; Dumas, Chimie Appliquée aux Arts, t. viii;
Wurtz, Dictionnaire de Chimie, 1872, art. Indigo; Indigo et son
Emploi, par De Kæppelin; Annales du Génie Civil, 1864, t. iii.;
Lectures of Dr. Grace Calvert, Chemical News, Aug. 9 and 23, 1872;
O’Neill’s Dictionary of Dyeing and Printing; Napier’s Chemistry
Adapted to Dyeing; Muspratt’s Chemistry Applied to the Arts,
articles Indigo and Dyeing; Ure’s Dictionary of Manufactures, ed.
of 1860; Proceedings of Royal Society, vol. xvi.; Proceedings of
Literary and Philosophic Society of Manchester, vol. iv.; McCulloch’s
Dictionary of Commerce, ed. 1869; Dictionnaire Universel du
Commerce, &c., ed. 1861; _South Carolina Production_.—Ramsay’s
History; Drayton’s South Carolina; Silliman’s Journal, vol. xviii.
A more complete bibliography is given in Schutzenberger’s work.