We entered upon the subject of indigo, which we have treated at some
length in our last issue, as much in the interest of the people as of
manufacturers, for we were deeply impressed with the conviction that
no improvement in our manufacturing processes would confer more
benefit upon the masses than imparting stability of color to the
clothing of the people. When one has a deep conviction upon a subject,
upon which others have equal opportunities for judging, he may be sure
that he is not alone in his impressions. He is moved by one of those
waves of thought which, operating simultaneously upon many minds,
gives that uniformity to public opinion at which we so often wonder.
We are gratified to find, from responses to our last article, that we
are not alone in our conviction of the importance of reviving “true
blue” dyes. The head of a mercantile house, the extent of whose
_clientèle_ in mills both of wool and cotton is hardly surpassed, has
assured us that we have not overstated the reform in dyeing which we
have advocated. He had long shared in our convictions. Pointing to the
throng of men in the crowded street, where we were conversing, he
remarked that there was hardly a man in the crowd whose clothing would
not have been improved by indigo dye. “The failure to use indigo
dyes,” he emphatically said, “costs the laboring people of this
country millions of dollars every year. The fault is not to be charged
to our own manufacturers alone; for the blue coat which I wear, and
which I bought in Paris, annoys me by the crocking caused by its
aniline dye.” In one very large mill of which he is director as well
as selling agent, he is putting his principles in practice. All the
heavy blue cloths intended for popular consumption are faithfully
dyed, and each bears a stamp, “Warranted indigo dyed.” The ready-made
clothing establishments which largely consume these goods have already
found their advantage in purchasing them, and a similar stamp is
attached to each article made from this cloth.
Some of our most celebrated cotton fabrics have won and still retain
their reputation by the use of indigo dyes. The ginghams are a signal
illustration. The blue check is formed by weaving cotton yarns dyed
blue in the cold indigo vat with undyed yarns. These goods can be
washed indefinitely without change.
Another illustration is the famous A.B.A. Amoskeag tickings, an
article of such excellence that the question of the right to use
trade-mark A.B.A. gave rise to the leading American case in this
branch of law.[3] A prominent feature in these goods was and still is
the permanence of the dye in the blue stripe, produced by the cold
indigo vat. Still another illustration is the blue and white “shirting
stripe” first made by Mr. Samuel Batchelder, at the Hamilton Mills,
now so generally adopted for sailors’ shirts. The indigo dye enables
the color to resist the roughest possible usage.
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[3] See the case stated at length in our article on Trade-marks,
Bulletin, vol. i. p. 102.
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To recur to the application of indigo dyeing to wool and woollens. We
have been unable, although we have written more than fifty letters of
inquiry upon the subject, to learn of any peculiarity or improvements
in the American processes of wool dyeing with indigo.[4] Our dyers are
for the most part foreigners. For this reason, or because the art of
indigo dyeing has long since reached perfection in the best
establishments abroad, they rigidly pursue the old European methods.
The best dyers regard the successful management of the warm fermenting
vats for wool as the highest test of their art. We have already spoken
of the complicity of the phenomena in fermentations. Practical dyers
endow the fermenting vat with a sort of personality. “An indigo vat,”
says one to us, “is more like a sick man than any thing in the world:
you have to watch it as you would a sick patient, and give it physic
or ferments to stir up the system and purify it.” [5] The diagnosis of
a sick vat requires that sort of instinctive knowledge which
experience gives to the practised physician. The impatience of our
young Americans will not permit them to serve the long apprenticeship
necessary to acquire the proper experience. The artisans not
thoroughly trained will naturally prefer the dyes and processes
introduced by modern science, which require but little skill in their
application. It is a curious fact that the influence of the national
government has been largely instrumental in preserving the old system
of indigo dyeing. Thanks to the Quartermaster-General’s Bureau, or the
man of science, General Meigs, who presides over it, indigo dyed
cloths have been persistently insisted upon for the army. The late war
gave a new impulse to indigo dyeing. A skilled dyer, whom we have
consulted, was constantly employed in Connecticut, on a tour of
professional inspection of a dozen or more different establishments
making army goods. No doctor, he says, ever found in hospital practice
more complications of disease than he found in the ailing vats. Among
other difficulties there was a deficiency of imported woads, although
the cultivation of excellent woad immediately sprung up in
Connecticut. In the mean time carrot and rhubarb tops were used as
substitutes for the fermenting material of the woad. Carrot-tops grown
expressly for that purpose brought as high as twenty-five cents per
pound. Since the war the requisitions for indigo dyed woollen goods
have not relaxed, and the art is not likely to be lost.
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[4] A reply by Mr. D. R. Whitney, an extensive indigo importer,
to a letter of inquiry, enables us to correct some errors in our
former article, under the head of “commerce in indigo.” The value
of export from India in 1862–63, stated in dollars, through a
typographical error, should have been pounds sterling; thus,
instead of $2,126,814, read £2,126,814. It is stated in our first
article that the telegrams show a decline of price of indigo in
the Indian trade of from 50 to 75 per cent; “per cent” should
read “rupees,” which would make a decline of from 25 to 30 per
cent. The reason for the decline, as stated by Mr. Whitney, is
the unusually large crop of this year. The average crop of indigo
in Bengal is about 100,000 maunds. The crop of this year is
135,000 maunds, about 30 to 35 per cent above the average.
According to Mr. Whitney, the consumption of Bengal indigo in the
United States was 2,458 cases of 270 lbs. to a case on an
average, in 1871; and in 1872, 1,802 cases. Guatemala indigo,
3,132 serroons in 1871, and 2,578 serroons in 1872.
[5] See notes on “sickness” of vats in Appendix.
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With the real difficulties which attend the process, it is hard for
indigo dyeing to sustain itself in the face of cheap substitutes of
easy application, such as the Nicholson blue. It is exceedingly
difficult to piece dye with indigo and preserve a uniform hue upon the
cloth. Hence indigo dyes are generally given in the wool. The wool
absorbing the foreign material of the dye is more difficult to work in
the operations of carding and spining. In other words, a finer and
costlier wool is required. A great _desideratum_ therefore is a means
of piece dyeing with indigo so as to preserve a perfect uniformity of
hue throughout the piece. This, we are happy to say, has been recently
successfully accomplished by one of the largest and most faithful of
our cloth-making establishments. It would be premature, before the
patents are secured for this invention, to explain the ingenious and
expensive apparatus devised for this purpose, which constitutes in
fact a battery of vats so arranged that the operation may be
continuous. The experiments authorize the statement that bottom dyes
of indigo, so desirable for a great variety of colors, can be applied
with no other additional cost than that of the dyeing material. When
this establishment, as it proposes, stamps upon the cards which
designate goods, already so admirable in material and texture,
“Warranted indigo dyed,” we shall regard it as an era in the American
card-wool manufacture.
The old European woad vat process is that used in all our
establishments. Mr. Henderson of the Washington Mills, whose
experience as a practical dyer of wool is exceptionally large, informs
us that he has found no work so instructive upon this process as
Napier’s “Chemistry of Dyeing” (published by Henry Carey Baird, of
Philadelphia, 1869). Napier’s description of the process is extracted
from Dumas’s “Lectures on Dyeing.” The appreciation expressed by so
competent a judge induces us to reprint Dumas’s description in an
appendix to this article.
That we may give at least a general view of the whole subject, we will
proceed to consider indigo in some relations not yet adverted to.
In Part I. of our notes we have treated only of the application of
this substance in dyeing by means of reduction through the indigo vat.
Indigo may be applied by means of reduction in the printing of
fabrics, as well as in dyeing them. A true scientific arrangement
would compel us next in order to consider this other application of
indigo by means of reduction. But the more natural and practical order
is to pursue the subject of dyeing, and to consider next the
applications of the derivatives from indigo in dyeing proper.
SULPHURIC DERIVATIVES,—SAXON BLUE, &C.
The powerful action of sulphuric acid upon indigo, and the bright and
lively blue color thereby produced, had been observed by chemists long
ago; but no person appears to have applied this color upon cloth,
until it was done about the year 1740, by Counsellor Barth, at
Grossenhein, in Saxony. The vividness of the dye, and the facility
with which it was applied, brought it into great vogue under the name
of Saxon blue, from its origin. Its popularity in former times is
evinced by the words of the old song, “The Blue Bells of Scotland:”—
“In what clothes, in what clothes is your Highland laddie clad?
His bonnet’s of the Saxon blue, his waistcoat of the plaid.”[6]
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[6] First sung by Mrs. Jordan, about the year 1799.
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The Saxon blue consists simply of a solution of indigo, the Guatemala
blue indigo being preferred, in sulphuric acid suitably diluted with
water. The result of this reaction is not a single chemical substance,
but two acids giving different tints, one called _sulpho-purpuric_
acid or _phenicine_, and the other _sulpho-indigotic_ acid; the first
giving to wool a reddish-violet color, and the other a pure blue. A
third compound has been indicated by Berzelius, the nature of which
has not been determined. Whether one or the other of the two named
acids, or the two combined, shall be produced by the reaction between
the sulphuric acid and the indigo, depends upon the duration of the
contact, the temperature of the mixture, and the nature and proportion
of the acid used.
Persoz gives the following general receipt:—
“1 part by weight of indigo, finely rubbed.
1 „ „ „ „ Nordhaussen acid.
1 „ „ „ „ ordinary sulphuric acid.
Leave for forty-eight hours, then heat until a drop turned into
water will dissolve without producing a precipitate. Leave to cool,
and dilute with water till the strength is brought to 18 Beaumé.”
Napier says that he has found the following method of preparing
sulphate of indigo, in quantities for use, very satisfactory: “The
indigo is reduced to an impalpable powder, and completely dried by
placing it on a sand bath or flue for some hours at a temperature of
about 150° F. For each pound of indigo six pounds of highly
concentrated sulphuric acid are put into a large jar, or earthen pot,
furnished with a cover. This is kept in as dry a place as possible,
and the indigo is added gradually in small quantities. The vessel is
kept closely covered, and care taken that the heat of the solution
does not exceed 212°F. When the indigo is all added, the vessel is
placed in such a situation that the heat may be kept up at about
150°F., and allowed to stand, stirring occasionally, for forty-eight
hours. These precautions being attended to, we have uniformly found
that any failure occurring was clearly traceable to the impurity of
the indigo or weakness of the acid used.”
The processes for producing and separating the two acids derived from
the combination of sulphur and indigo are minutely given by Berzelius,
in vol. i. of his “Traité de Chemie,” who states this curious fact
illustrative of the peculiar affinities of wool with certain dyeing
substances. Wool or flannel thoroughly scoured, when immersed in the
blue solution of indigo with sulphuric acid, acts as a base: it
combines gradually with the acid blue, and becomes itself colored of a
deep blue. When saturated with color, it is withdrawn. Fresh wool is
introduced until the bath yields no more color. If sublimed or
perfectly pure indigo is used, there remains in the bath nothing but
free sulphuric acid. The wool thus plays the part of a base with which
the blue acids combine. The dyed wool is afterwards washed and treated
in feeble alkaline bath (ammonia), which redissolves the blue. This
method of purifying the Saxon blue is still practised by French
manufacturers.
The combination of indigo with sulphuric acid, sometimes improperly
called sulphate of indigo, is known by the dyers here and in England
under the name of _chemic_. The name of _chemic_ blue or green is also
given the dyes formed from the indigo extract hereafter spoken of. It
is largely used for making certain greens required in Scotch plaids.
The old Saxon blue or simple solution of indigo with sulphuric acid is
now seldom prepared by the manufacturers themselves. It is now
generally prepared for them, and furnished commercially under the name
of _indigo extract_. The finer qualities used for fine dyeing and
printing are known under the name of _carmines_ of indigo, _neutral
extract_, _soluble indigo_, _ceruline_, &c.
The production of indigo carmines, which are simply alkaline
sulphindigotates or sulpho-purpurates, is founded upon their
insolubility in a liquid charged with a salt.
If, for example, we dissolve one part of indigo in four parts of
fuming acid, and dilute the liquid with sixty or eighty times its
weight of water, it will contain, besides the _sulphindigotic_ acid,
an excess of sulphuric acid. By adding one part of crystals of soda so
as to neutralize the bath, there will be formed not only
sulphindigotate of soda, but sulphate of soda: as the former is
insoluble in the saline liquid, the presence of the sulphate of soda
causes the precipitation of the sulphindigotate in deep blue
floccules. These are collected on woollen filters and washed to remove
the sulphate of soda and a green coloring material, probably a
modified chlorophyl, which the paste often contains, and which has the
singular property of fixing itself on silk, but not on wool.
The carmines are divided according to their richness in indigo into
simple carmine (4.96 per cent of indigo, water 89, saline materials
57), double carmine (10.2 per cent indigo, water 85, salts 4–8),
triple carmine (12.4 per cent indigo water, 73.7, salts 13.9). A
species of solid carmine known as Boiley blue or purple is in high
repute in France.
The carmines may be tested by dyeing a specimen of wool in an
acidulated bath to which cream of tartar has been added. The presence
of the green matter, so objectionable to silk-dyers who make much use
of these carmines, is detected by rubbing a small quantity of the
carmine on a piece of glazed paper, which, when the color dries, gives
a color varying from blue to a rich copper color: if any green
coloring matter is left, it shows itself by a green aureola around the
blue color. The method of applying the carmines in dyeing wool and
silk,—for they are not adapted to cotton fabrics,—as given by M. de
Kæppelin, is as follows:—
The operation is conducted in small wooden vats, provided with
openings for manipulation, and pipes for inducting steam to heat the
baths to the proper temperature. It consists of two parts, that of
mordanting and dyeing. The former is thus conducted.
For each kilogram of tissue which has been previously scoured and
bleached, there are provided 200 grammes of cream of tartar and 250
grammes of alum. These are dissolved in the bath of water of the vat,
the temperature is raised to boiling heat, and the tissue is immersed
in the bath f of an hour while it is worked over through the opening
for manipulation. The pieces are then taken from the bath, to which is
added a solution of the carmine in water containing a quantity of
coloring matter proportionate to the intensity of the blue sought for.
The solution ought to be prepared with care and passed through a silk
sieve, so that the small insoluble grains which might have been left
through bad fabrication may be left on the sieve. After the pieces
have been manipulated in the colored bath, so as to exhaust the color
and obtain the required blue, they should be rapidly washed in running
water and dryed in the shade. Silk stuffs are dyed in the same way;
but the alum should be previously applied cold by means of a saturated
solution of alum, in which the stuffs should be immersed for an hour.
COLORS NOT FAST.
In regard to all the combinations of indigo with sulphuric acid,
including the carmines, it must be observed that their application
does not constitute true indigo dyeing: the colors are not fast. It is
not pure indigotine which is fastened on the tissues as in the vat
dyeing, but another compound of indigo with the sulphur. Berzelius
observes that “the color of soluble indigo is fully as alterable and
fugacious as that of the colors extracted by the decoction of
vegetable materials. By a long exposure to the sun the indigo blue is
destroyed: it becomes green during evaporation, and changes its
nature.” The carmines as well as the sulphur acids are easily
decolorized by reducing agents, such as hydrogen and sulphuretted
hydrogen, although they gradually assume their original color when
exposed to the atmosphere. We are informed by some of the older
dealers that imported cloths and merino stuffs known as “Saxony” were
formerly largely sold in our shops, but that, notwithstanding their
attractiveness to purchasers, they were objectionable on account of
the instability of their color.
APPLICATION OF INDIGO IN PRINTING STUFFS.
Our notes would be incomplete without some reference to the uses of
indigo in printing fabrics. In pursuing this branch, we are
embarrassed on the one hand by the consideration that the subject is
too technical for the general reader, and on the other by the
consciousness that it would be presumption in us to attempt to
instruct those skilled in the art. It may not, however, be without
benefit in producing a higher appreciation of science for the general
reader to observe how science comes in play, even in the printing of a
single color; while to the skilled reader our notes may possibly be of
value as a vehicle for conveying some receipts taken from works not
easily accessible.
PRINTING STUFFS OF WOOL AND SILK, AND STUFFS WITH COTTON WARPS.
This branch of our subject is directly allied to the one last
considered, the application of the compounds of sulphur and indigo;
for indigo is applied to printing wool and silk principally in the
form of indigo carmines. These applications are less numerous than
they were formerly, since they have been replaced by Prussian blue,
and more recently by the aniline blues, which are now generally used.
When the carmines are used, it is for making sky blues, and they enter
into the composition of some greens and browns. The salts of alumina
and vegetable acids are used to fix the indigo carmine upon tissues of
wool and silk. Some receipts recommended by M. de Kæppelin, himself a
practical printer, are given in a note.[7]
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[7] BLUE NO. 1.
Indigo carmine 400 grammes.
Alum 100 „
Oxalic acid 150 „
Boiling water 1¼ litre
Gum water prepared in proportion of
1 kilogram to the litre 1¼ litre
GREEN NO. 1.
Gum water as above 12 litres.
Cuba lac 12 „
Alum 1 kilogram, 500 grammes.
Oxalic acid 2 „
Indigo carmine 4 „
BOUILLON FOR THE GREENS AND BLUES.
Boiling water 12 litres.
Alum 600 grammes.
Oxalic acid 750 „
Gum water 12 „
SKY BLUE FOR WOOLLEN STUFF WITH COTTON WARP.
First solution.—Boiling water 4 litres.
Cyanuret of iron and potash 800 grammes.
Second solution.—Boiling water 2 „
Tartaric acid 300 „
Third solution.—Cold water 3 „
Sulphuric acid 300 „
Pour in the first solution, then the second and third, agitating the
color with a spatula after each new addition.
The following mixture is afterwards applied to the stuff:—
Gum water 12 litres.
Water 6 „
Blue No. 1 for wool 3 „
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In printing tissues of wool with cotton warp, the carmines are not
used alone. They are combined in certain proportions with cyanites of
iron and potash, to obtain upon the cotton a blue color of equal
intensity with that produced by the carmines upon wool. It is also
necessary to previously mordant the fabrics by means of a solution of
oxide of tin or caustic soda which is precipitated on the fibres by
passing through a bath of water, to which sulphuric acid has been added.
APPLICATIONS OF INDIGO IN PRINTING COTTON FABRICS.
Before entering upon methods used in large establishments, it may not
be without interest to observe the processes still used in Java for
printing calicoes, which the natives prefer to any imported from
Europe. In Java there are no factories, and the women in each family
make and dye or print all the cotton cloths required for their own
consumption. They apply by means of a brush or pencil, which they use
with great skill, to the cotton tissue which they wish to cover a thin
coating of wax mixed with a little resin, the wax being applied to all
the parts where the design, which has been first traced upon the
cloth, requires that the fabric should remain uncolored. They then
immerse the stuff several times in an indigo vat until they have
obtained the desired tint. The stuff is afterwards washed and dried
for a new application of the wax, carefully applied with a pencil as
before. The cloth is then immersed in a bath of a different color,
made with madder or catechu, but always of some dye which is perfectly
stable; and the operation is repeated according to the number of
colors desired. By these successive applications of wax and immersions
into different vats, they succeed in producing very complicated and
harmonious colors, while no European goods compare with them in
stability of dye.
In the European, and our own manufacture, the blue bottoms upon
vegetable fibres, made by immersion in the indigo vat, are combined
with white impressions, or others variously colored, by two distinct
methods. Sometimes there is printed upon the cloth before dyeing in
the indigo vat a preparation called a reserve or resist, which
prevents the indigotine from being deposited in the places where it is
applied. Sometimes, on the contrary, the indigo, which has been
uniformly fixed upon the fabric, is destroyed in certain places marked
out by printing upon them certain chemical agents, called _discharges_.
The _reserves_ are mechanical, resisting the penetration of the dye,
such as wax and pipe clay, or chemical. The last, through these acid
or oxidizing properties, cause the precipitation of the indigotine
before it has touched the fibre or penetrated into its pores. Such are
the salts of copper and bi-chlorate of mercury. Other bodies perform
the part both of mechanical and chemical reserves. The salts of zinc
or alumina, for instance, which are frequently used, produce at the
same time a deposit of indigo white and a gelatinous covering of
hydrated oxide of zinc or aluminium. The composition of a good reserve
is declared to be principally a question of good proportions of the
constituent parts, varying with the strength of the vat and the
intensity of the blue which is desired to be reserved. The first
condition is that it hardens immediately after immersion in the vat:
if it softens, on the contrary, it will cause the running of the
color. In other words, the acidity of the impression should be
proportionate to the strength and alkaline character of the vat. The
white reserve, that most generally used, is composed of pipe clay,
gum, verdigris, and sulphate of copper. The styles of work produced by
dipping with reserves are generally of a cheap and low class. The
system is clumsy and expensive, and is only tolerated because of the
want of a method of directly applying indigo, which will yield the
deepest shades.
Certain styles, formerly in great vogue, called _Lapis_, and forming
one of the richest branches of the cotton-printing industry, are
founded upon the use of reserves; and in these styles, by very simple
means which we shall not attempt to describe, different colors
produced from madder, catechu, &c., are produced upon the fabric so
perfectly surrounded by blue that the eye cannot detect the slightest
want of continuity. This fabrication has the greatest perfection in
Russia. The imitation cashmere fabrics of cotton imported from that
country, formerly much in fashion for dressing-gowns, are specimens of
this fabrication. The great stability of the colors is a remarkable
feature of these goods.
The system of resists or reserves possesses the inconveniences of not
producing impressions of great firmness, and of requiring very strong
vats. When the strength of the vat is partially exhausted, they may be
thrown aside. These inconveniences are obviated by the system of
discharges (_enlevages_). In this system the cloths are vat dyed of a
uniform blue. The strength of the vat is of less importance, and it
can be used until the indigo is quite exhausted. The means of
destroying the indigo which has been fixed upon the fibre are founded
on the use of active oxidizing agents, which transform the insoluble
indigotine into soluble isatine. The agent generally used is chromic
acid. As this acid cannot be incorporated with the thickening to be
printed, as the thickening would produce oxide of chrome, the cloth is
passed through a strong solution of chromate of potash, and dried in
the shade. The required pattern is then printed on the cloth with a
mixture whose principal elements are acids which are susceptible of
setting free the chromic acid on the tissue, which then acts upon the
indigo producing a white pattern. The acid generally employed for
freeing the chromic acid is oxalic acid, thickened with British gum,
dextrine, or starch, with the addition of pipe clay. To prevent
running, nitric, sulphuric, or tartaric acid are sometimes used.[8]
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[8] Schutzenberger gives the following receipts:—
PREPARATION FOR DISCHARGE.
Water 2 litres.
Yellow chromate 500 grammes.
WHITE DISCHARGE ON BLUE BOTTOM.
Tartaric acid 3 kilograms.
Oxalic acid 250 grammes.
Burnt starch 4 kilograms.
Nitric acid 500 grammes.
Water 4 litres.
De Kæppelin gives the following:—
WHITE DISCHARGE ON BLUE.
Water 2 litres.
Starch 1 kilogram, 800 grammes.
Oxalic acid 500 grammes.
Tartaric acid 250 grammes.
Sulphuric acid 375 grammes.
The pieces, having been dyed blue, are then placed in a solution of
bichromate of potash in water, which is prepared in the ratio of 50 to
60 grammes to the litre, according to the intensity of the blue. The
pieces thus prepared must be dried away from direct solar light or too
much heat. In fact, under the action of these agents, the bichromate
would be decomposed and the tissue altered. The pieces are often
rolled up to prevent this effect. After the pieces are printed, they
are passed into a vessel containing water and holding chalk in
suspension in sufficient quantity to give it a milky aspect. The
temperature of the bath is raised to 60° R. The excess of acid of the
color applied is saturated by the chalk, and the excess of bichromate
of potash with which the tissue is impregnated is dissolved in the
bath. The pieces are afterwards washed and passed through slightly
soapy water.
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By the method of discharges the white designs upon blue are brought
out with a distinctness which it is impossible to obtain by resists,
while the most delicate work of the graver can be exactly reproduced
upon the tissue.
APPLICATION OF INDIGOTINE BY PRINTING.
The first step in the art of printing indigotine upon calicoes was the
application of what is called pencil blue. Instead of immersing the
fabrics in an indigo vat, the indigo white formed in a very strong
indigo vat was thickened and applied locally to certain places on the
cloth. The preparation was painted upon the cloth by means of pencils
made of willow sticks, the ends of which were broomed up into a kind
of brush. The style was hence called pencil blue. The methods now used
to apply white indigo locally are of two kinds. The china blue
process, and the solid blue process, sometimes called fast or
precipitated blue. The china blue process derives its name from the
resemblance of its color to the blue on the old china ware. It has
great depth of tint, and permanency. It is scarcely used now, except
for certain articles requiring great depth of color, such as certain
furniture goods, and by the Germans and Swiss for the manufacture of
calicoes for exportation to India.
We do not venture to condense the descriptions at our hand of the
processes for applying the china blue and the solid blue, and
translate those furnished by chemists of high authority. After the
method indicated by Darwin in his recent works, we present them in
smaller type, with the perhaps unnecessary suggestion that they may be
passed over by the general reader.
_China blue_.—The theory of this printing blue, says Schutzenberger,
is very simple. The indigo, reduced to an impalpable powder and
thickened, is printed by a plate or roller. After drying, the tissue
seems dyed blue, more or less deep, according to the proportion of
coloring material used; but it is only a blue of application, which
can be removed with the thickening, by the slightest washing. The
object is now to reduce and redissolve the indigotine in place to
enable it to penetrate the fibre at the end of a consecutive
oxidization, and without producing a running of the color or altering
the purity and distinctness of the contours of the design. I owe to M.
Ed. Schwartz some valuable hints upon the fabrication of this style,
which is also described with much care and details in the treatise on
printing by M. Persoz.
The reduction of the indigo is obtained by alternate passages of the
printed tissue into vats containing,—the first, quicklime slacked; the
second, sulphate of iron; the third, soda. The operation is terminated
by a passage through a bath of sulphuric acid, which removes the oxide
of iron and precipitates the indigo white by hastening its oxidation.
The success depends upon the composition of the color printed, and
above all upon the strength of the vats of immersion and the duration
of the treatment.
The operator uses six vats,—for instance, two lime vats, provided each
with 12 kilograms of lime; a copperas vat at 70 Beaumé; a caustic soda
vat marking 140 Beaumé; a sulphuric acid vat with 500 grammes of acid
(_par mesure d’eau_); and finally a vat of pure water.
The receipts for printing are:—
1. THE BLUE PREPARATION.
Ground indigo 4 kilograms.
Acetate of iron 10 litres.
Sulphate of iron 1 kilogram.
Water 10 litres.
Gum Senegal 6 kilograms.
Pass through a sieve; leave some time at rest, and stir whenever used.
Caraccas indigo is preferred because it can be broken into a finer
powder and gives a finer paste.
2. COLORS FOR ROLLER PRINTING NOS. 1, 2, 3, 4.
The blue preparation above 1, 1, 3, 4.
Acetate of iron containing 700 grammes of gum per litre 2, 1½, ½, ½.
Gum water at 600 grammes per litre 16, 2½, ½, ½.
These proportions can be varied according to the tint desired.
The piece is treated a quarter of an hour in the first lime vat by
giving it a light movement from above to below; it is left a quarter
of an hour in repose in the sulphate of lime vat; a quarter of an hour
in the second lime vat; a quarter of an hour in the copperas vat; five
minutes in the caustic soda; half an hour in the sulphuric acid, and
then thoroughly rinsed.
To each lime vat there is given 2 kilograms of lime per piece of
cloth. To the vitriol vat there is added 50 kilograms of sulphate of
iron for each dozen pieces. The soda vat is renewed after 5 pieces by
the addition of 12 kilograms of salt of soda, which has first been
made caustic. The acid vat receives 25 kilograms of acid after 5
pieces, and ought to be renewed whenever it becomes saline. The other
vats must be cleared out whenever the deposit becomes too great for
success.
M. Ed. Schwartz recommends as important conditions, (1) the perfect
causticity of the tissue, and an average strength of 140 Beaumé; (2)
the neutrality of the sulphate of lime vat. For this end old iron
should be boiled in it.
After leaving the sulphuric acid vat the pieces are rinsed in the
water vat, then in river water, and afterwards should be soaked in a
sulphuric acid bath at 40 Beaumé, for the purpose of dissolving the
last traces of the peroxide of iron adhering to the fibre. The fabric
is then washed in water and finally passed through a soapy water at
40° R.
_Solid or precipitated blue, Schutzenberger’s receipt_.—The process
consists in printing indigo white precipitated in a vat, in a thick
paste to dissolve it on the tissue by a passage through an alkaline
bath (lime or soda), and of reprecipitating it by oxidizing it as soon
as it has entered the fibre.
It is then the china blue process, minus the reduction which is made
before printing, and consequently minus the sulphate of iron vat.
Indigo white is too alterable to be printed with success, so it is
generally precipitated in combination with a stannic hydrate (hydrate
of a salt of tin), which gives it body and preserves it from a too
rapid oxidation.
The stannic indigotate in paste, or as it is generally called
precipitate of indigo, is prepared by turning into the clear portion
of a strong copperas vat an acid solution of protochlorate of tin, and
filtering it upon woollen filters,—as much as possible away from the
air. It would be better to prepare a strong tin vat by heating a
mixture of indigo, caustic soda, and protochlorate of tin, and to
precipitate by chlorohydric acid.[9]
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[9] Mr. T. P. Shepard gives in his valuable “Receipts for Calico
Printing,” published in 1872, the following:—
NO. 52. INDIGO PRECIPITATE FOR FAST BLUE AND GREEN.
10 pounds quicklime, slacked with
6½ gallons water; then
2 pounds ground indigo finely rubbed in water are stirred in; then add
6 pounds copperas dissolved in 5 gallons of water; then add
5 gallons hot water and
15 gallons cold water.
Stir well from time to time, until the liquid has assumed a yellow
color and deep blue veins or streaks appear on its surface. When this
moment arrives, draw off the clear liquor, and precipitate every ten
quarts of it with
½ pound tin crystals, dissolved in ½ pound muriatic acid.
To the remainder of the mixture of lime and indigo, 15 gallons of
water may be added, and the whole stirred; and when settled, the
indigo may be precipitated from the clear liquor as before. This
operation may be repeated a second time before all the indigo is
exhausted.
The indigo precipitate is to be collected on a muslin filter, and
well squeezed out.
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The deposit is made into a paste with gum water; a salt of tin is
often added to prevent oxidation. It is important to prevent the
transformation of the indigo white into indigotine before printing.
This indigotine would not fix itself on the fabric. Moreover, after
printing, it is necessary to hasten the dissolution of the indigo
white to enable it to penetrate the fibre. It is sufficient for this
end to pass it through milk of lime. The stannic combination is
immediately destroyed; the colorable matter unites itself with the
lime, and the color passes into a pale gray with apple green. The
indigo white becomes momentarily soluble; but the presence of the
excess of lime and the thickening, as well as the attractive affinity
of the thickening, prevent any running.
The piece on issuing from the lime water is placed in running water,
when reoxidation commences, which this time fixes the color. The piece
is finally passed through a sulphuric acid bath to absorb the lime,
and washed.
By adding to the color a salt whose base precipitates in the milk of
lime and oxidizes in the running water, and replacing the simple acid
bath by an acid bath with yellow prussite, the intensity of the blue
is increased through the formation of Prussian blue.
Although we have seen beautiful effects from the application of the
solid blue of indigo on prints at our Pacific Mills, the colors
produced by Prussian blue and aniline are so much more brilliant and
easy of application that the use of indigo in printing goods for
ordinary consumption is likely to decline rather than increase. It
will be otherwise if we should ever manufacture for the East India
markets. Here is a field still open for our manufacturers. Mr. Watson,
in his beautiful work on “The Costumes of the People of India,”
remarks that “British manufacturers have hitherto failed to appreciate
Oriental tastes and habits, and hence supply but an insignificant part
of the clothing of the two hundred million persons that form the
population of what is commonly spoken of as India.” The great defect,
he observes, is the want of stability of color in the cotton fabrics
introduced,—this stability being an imperative demand in the Oriental
markets.
The applications of indigo to cotton fabric are altogether secondary,
in our mind, to its relations to the woollen manufacture. If we have
felt called upon to say a word in behalf of the most ancient and best
ally which the fibre of wool has ever had, it is because the vividness
of color of the new products of coal, and the fascination which the
application of the recent discoveries of science always possesses, is
threatening the eclipse of the more ancient sober and solid dyes. Let
the new colors have their place as auxiliaries, not as substitutes for
the ancient dyes. Let them serve to give a bloom[10] to goods, but let
the foundation be the good old dyes which the experience of ages has
proved to be the most unalterable by light and air. The recent
wonderful discovery of alizarine, or artificial madder, in coal tar
products, has led practical men to expect too much from science. The
opinion is quite prevalent among manufacturers that artificial
indigotine has already been obtained from the same source. And some
manufacturers are sanguine that the difficulties of indigo dyeing will
thus be resolved. It is not improbable—for what is impossible to
modern chemistry?—that this result will yet be partially obtained. But
we have looked over all the recent foreign chemical reviews, and
personally consulted some of our best chemists, and we can find no
authority for the prevailing opinion that artificial indigotine has
been produced. If the production of artificial indigotine should be
realized, the only benefit would be the possible cheapening of the
material. The difficulties of the indigo vat would still remain; for
we cannot too often repeat, that in the very difficulties of the
process, or in the insolubility of blue indigotine by ordinary agents,
consists the excellence of the dye.
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[10] _Guernsey Blue_.—The darkest of the Nicholson Fast Blues. On a
bottom of barkwood, camwood, madder, or inferior _indigo_, produces
an indigo blue which will stand all the acid tests the same as
colors made from indigo.
_Serge Blue_.—It will be found very serviceable to give bloom to
goods dyed with indigo, and by itself shows a very good indigo test
with nitric acid.—_Instructions for Working the Atlas Works Aniline
Dyes_.
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APPENDIX.
DYEING WOOL IN THE WARM INDIGO VAT.
[_Extract from Dumas’s Lectures on Dyeing_.]
The value attached by practical wool-dyers to the following induces us
to publish it without condensation:—
Indigo Blue.—We give a solid dye of indigo blue to wool by plunging it
into an alkaline solution of indigo white, and then exposing it to
contact with the air. The solution of indigo white is prepared in a
vessel usually from eight to nine feet in depth, and six to seven feet
in diameter. This size is very convenient for the requisite
manipulations, and presents a large volume of water, which, when once
heated, is capable of preserving a high temperature for a long time.
This vessel should be made of wood or copper. It always bears the name
of vat. These vats are covered with a wooden lid, divided into two or
three equal segments. Over this lid are spread some thick blankets.
Without this precaution the bath would come in contact with the
atmospheric air, a portion of the indigo would absorb oxygen and
become precipitated. There would also be a great waste of heat.
A most necessary operation, and one which has to be frequently
repeated, consists in stirring up the deposit of vegetable and
coloring matter which is formed in the vat, and intimately mixing it
in the bath. For this purpose we employ a utensil called a _rake_,
which is formed of a strong square piece of wood, set on a long
handle. The workman takes hold of this with both hands, and, dipping
the flat surface into the deposit at the bottom of the vessel, he
quickly draws it up until it nearly reaches the surface, when, giving
it a gentle shake, he discharges the matter again through the liquor
of the bath. This manœuvre is repeated until the whole of the deposit
seems to be removed from the bottom of the vessel. Before the tissue
is dipped into the dye-bath, it should be soaked in a copper full of
tepid water; it is then to be hung up and beaten with sticks. In this
state it is plunged into the vat; it thus introduces less air into the
bath, while it is more uniformly penetrated by the indigo solution.
The cloth is now kept at a depth of from two to three feet below the
surface of the liquid, by means of an open bag or piece of network
fixed in the interior of an iron ring, which is suspended by cords,
and fixed to the outside of the vat by means of two small iron hooks;
the bag is thus drawn backwards and forwards without permitting it to
come in contact with the air. When this operation has been continued
for a sufficient length of time, the cloth is wrung and hung up to dry.
Flock wool is also, for the purpose of dyeing, enclosed in a fine net,
which prevents the least particle from escaping, and which is fixed in
the bath in the same way as in the foregoing case.
The many inconveniences attending the use of wooden baths, which
necessitate the pouring of the liquor into a copper for the purpose of
giving it the necessary degree of heat, have led to the general
employment of copper vessels. These are fixed in brickwork, which
extends half way up their surface, whilst a stove is so constructed at
this elevation that the flame shall play around their upper part. By
this means the bath is heated and kept at a favorable temperature
without the liquor being obliged to be removed.
The potash vats are usually formed of conical-shaped coppers,
surrounded by a suitable furnace. These may be constructed with less
depth, inasmuch as there is less precipitation induced in the liquor.
By using steam for heating the vats, we might dispense with the
employment of copper vessels, and so return to those of wood.
The vats employed for dyeing wool are known under the names of the
pastel vat, the woad vat, the potash vat the tartar-lee vat, and the
German vat.
Pastel Vat.[11]—The first care of the dyer in preparing the vat should
be to furnish the bath with matters capable of combining with the
oxygen, whether directly or indirectly, and of giving hydrogen to the
indigo. We must, however, be careful to employ those substances only
which are incapable of imparting to the bath a color which might prove
injurious to the indigo. These advantages are found in the pastel, the
woad, and madder. This latter substance furnishes a violet tint when
brought into contact with an alkali, and by the addition of indigo it
yields a still deeper shade.
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[11] The distinction between pastel and woad is not very clear.
Schutzenberger says: “Pastel, woad, and satis tinctoria is a _plant_
of the family of the crucifera. It would seem, however, that the term
_pastel_ as used by the old French dyers is applied to the leaves of
the woad which have been fermented, formed into paste, and afterwards
into balls, and which contain much blue coloring matter. And the term
_woad_ as distinguished from _pastel_ is applied to the unfermented
plant.”
----------------------------------------------------------------------
In preparing the Indian vat, we ordinarily employ one pound of fine
madder to two pounds of indigo. The madder is here especially useful,
by reason of the avidity of some of its principles for oxygen.
The pastel vat, when prepared on a large scale, ordinarily contains
from 18 to 22 lbs. of indigo; 11 lbs. of madder would suffice for this
proportion, but we must also bear in mind the large quantity of water
which we have to charge with oxidizable matters. I have invariably
seen the best results from employing 22 lbs. to a vat of this size.
Bran is apt to excite the lactic fermentation in the bath, and should
therefore not be employed in too large a quantity; 7 to 9 lbs. will be
found amply sufficient.
Weld, which is often used, is rich in oxidizable principles; it turns
sour, and passes into the putrid fermentation with facility. Some
dyers use it very freely; but ordinarily we employ in this bath an
equal quantity of it to that of the bran. Sometimes weld is not added
at all.
In most dye-houses the pastel is pounded before introducing it into
the vat. Some practical men, however, maintain that this operation is
injurious, and that it interferes with its durability. This is an
opinion which deserves attention. The effect of the pastel, when
reduced to a coarse powder, is more uniform; but this state of
division must render its alterations more rapid. When the bath has
undergone the necessary ebullition, the pastel should be introduced
into the vat, the liquor decanted, and at the same time 7 or 8 lbs. of
lime added, so as to form an alkaline lye which shall hold the indigo
in solution. Having well stirred the vat, it should be set aside for
four hours, so that the little pellets shall have time to become
thoroughly soaked, both inside and out, and thus be prepared for
fermentation. Some think coverings are to be spread over the vat, so
as to preserve it from contact with the atmosphere. After this lapse
of time, it is to be again stirred. The bath at this moment presents
no decided character; it has the peculiar odor of the vegetables which
it holds in digestion; its color is of a yellowish-brown.
Ordinarily, at the end of twenty-four hours, sometimes even after
fifteen or sixteen, the fermentative process is well marked. The odor
becomes ammoniacal, at the same time that it retains the peculiar
smell of the pastel. The bath, hitherto of a brown color, now assumes
a decided yellowish-red tint. A blue froth, which results from the
newly liberated indigo of the pastel, floats on the liquor as a thick
scum, being composed of small blue bubbles, which are closely
agglomerated together. A brilliant pellicle covers the bath, and
beneath we may perceive some blue or almost black veins, owing to the
indigo of the pastel which rises towards the surface. If the liquor be
now agitated with a switch, the small quantity of indigo which is
evolved floats to the top of the bath. On exposing a few drops of this
mixture to the air, the golden-yellow color quickly disappears, and is
replaced by the blue tint of the indigo. This phenomenon is due to the
absorption of the oxygen of the air by the indigogen from the pastel:
in this state we might even dye wool with it without any further
addition of indigo; but the colors which it furnishes are devoid of
brilliancy and vivacity of tone, at the same time that the bath
becomes quickly exhausted.
The signs above described announce, in a most indubitable manner, that
fermentation is established, and that the vat has now the power of
furnishing to the indigo the hydrogen which is required to render it
soluble,—that contained in the pastel having been already taken up;
this, then, is the proper moment for adding the indigo, which should
be previously ground in a mill.
We stated above that the liquor of the vat should be previously
charged with a certain quantity of lime; we also find in it ammonia
generated by the pastel; but a part of these alkalies become saturated
by the carbonic acid gas along with the proper acids of the madder and
of the weld, as well as by the lactic acid produced by the bran during
fermentation. The ordinary guide of the dyer is the odor, which,
according to circumstances; becomes more or less ammoniacal. The vat
is said to be either soft or harsh; if soft, a little more lime should
be added to it. The fresh vat is always soft; it exhales a feeble
ammoniacal odor accompanied with the peculiar smell of the pastel; we
must, therefore, add lime to it along with the indigo; we usually
employ from five to six pounds, and, after having stirred the vat, it
is to be covered over. The indigo, being incapable of solution except
by its combination with hydrogen, gives no sign of being dissolved
until it has remained a certain time in the bath. We may remark that
the hard indigoes, as those of Java, require at least eight or nine
hours, whilst those of Bengal do not need more than six hours, for
their solution. We should examine the vat again three hours after
adding the indigo. We ordinarily remark that the odor is by this time
weakened; we must now add a further quantity of lime, sometimes less,
but generally about equal in amount to the first portion; it is then
to be covered over again, and set aside for three hours.
After this lapse of time, the bath will be found covered with an
abundant froth and a very marked copper-colored pellicle; the veins
which float upon its surface are larger and more marked than they were
previously; the liquor becomes of a deep yellowish-red color. On
dipping the rake into the bath, and allowing the liquid to run off at
the edge, its color, if viewed against the light, is of a strongly
marked emerald-green, which gradually disappears, in proportion as the
indigo absorbs oxygen, and leaves in its place a mere drop rendered
opaque by the blue color of the indigo. The odor of the vat at this
instant is strongly ammoniacal; we also find in it the peculiar scent
of the pastel. When we discover a marked character of this kind in the
newly formed vat, we may without fear plunge in the stuff intended to
be dyed; but the tints given during the first working of the vat are
never so brilliant as those subsequently formed; this is owing to the
yellow-coloring matters of the pastel, which, aided by the heat,
become fixed on the wool at the same time as the indigo, and thus give
to it a greenish tint. This accident is common both with the pastel
and the woad vats; it is, however, less marked in the latter.
When the stuff or cloth has been immersed for an hour in the vat it
should be withdrawn; it would, in fact, be useless to leave it there
for a longer time, inasmuch as it could absorb no more of the coloring
principle. It is therefore to be taken from the bath and hung up to
dry, when the indigo, by attracting oxygen, will become insoluble and
acquire a blue color. Then we may replunge the stuff in the vat, and
the shade will immediately assume a deeper tint, owing to renewed
absorption of indigo by the wool. By repeating these operations, we
succeed in giving very deep shades. We must not, however, imagine that
the cloth seizes only on that portion of indigo contained in the
liquor required to soak it. Far from such being the case, experience
shows that, during its stay in the bath, it appropriates to itself,
within certain limits, a gradually increasing quantity of indigo. We
have here, then, an action of affinity, or perhaps a consequence of
porosity on the part of the wool itself.
Woad Vat.—These vats are extensively employed at Louviers, and in the
manufactories of the north of France. The bath is prepared in the same
manner as in the foregoing case; the finely cut root is introduced
into the copper along with 2 lbs. of pounded indigo, 9 lbs. of madder,
and 15½ lbs. of slaked lime. The liquor is, after the necessary
ebullition, poured upon the woad. This substance contains but a very
small quantity of coloring principle; we must, therefore, add some
indigo when preparing the vat, so as to indicate the precise instant
when the mixture arrives at the point of fermentation so necessary for
imparting hydrogen to the coloring principle, and for rendering it
soluble. We must also use a larger quantity of lime, since the woad
contains no ammonia resulting from previous decomposition, such as we
find to be the case with the pastel of the south. When the vat is in a
suitable state of fermentation, a rusty color becomes manifest, in
addition to the signs already described in speaking of the pastel vat;
besides the ammoniacal odor, the bath always retains the peculiar
smell of the woad. The pounded indigo is now added, and we proceed, in
the manner already detailed, to reduce it to a state of solution fit
for dyeing.
The vats prepared by means of pastel have greater durability than
those made with the woad; but it is thought that the colors given by
the latter are more brilliant than those obtained from the former dye.
Modified Pastel Vat.—This vat is about 7 feet in depth, and 6½ feet in
diameter. It is made of copper, and heated by steam. The lid is
composed of three segments, each of which is formed of two planks,
about an inch thick, and strongly secured together by bolts.
The beating is performed in the usual way, with sticks before the
first dipping, after having moistened the cloth in tepid water. This
operation is not subsequently repeated.
This vat is prepared with 13 lbs. of indigo, 17½ lbs. of madder, 4½
lbs. of bran, 9 lbs. of lime, and 4½ lbs. of potash. Having filled the
vat, we heat it to about 200° Fah., and, as soon as the water is
tepid, introduce 441 lbs. of pastel. The liquor becomes of a
yellowish-brown color; small bubbles appear upon its surface,
ordinarily at the end of four hours if the vat be heated by steam, but
not until after eight or twelve hours where heat is applied by the
common fire; in the latter case the mixture should be stirred every
three hours. When the liquor displays the signs of fermentation, we
add the above-mentioned ingredients, and cover the vat over; it is
then to be set aside, stirring it every three hours, or oftener if the
fermentative action be very rapid. Each time that it is stirred we are
to add from 2 to 4 lbs. of lime; if fermentation proceed quickly we
even use more, but in the contrary case less. After about eighteen
hours, we plunge into the vat three pieces of common cloth, measuring
from twenty to twenty-five ells in length each; when they have
received six or seven turns, they are to be taken out again. The
object of this is to remove the excess of lime from the bath. The vat
is then set aside for three hours, when it is to be stirred, and 13
lbs. of indigo, with 2 lbs. of madder, added to it. We now again apply
heat to the mixture.
If the vat contains a superabundance of lime, it will be unnecessary
to add more; otherwise we throw in a further quantity. During the
night it should be covered with a cloth, and a workman left to watch
it. It is usually stirred once before the morning; but if it be
deficient in lime, it will require this manipulation to be more
frequently repeated, and also fresh lime added to it. On the following
day the stirring should be continued every three hours, and so on for
the next thirty hours, taking care to heat the vat from time to time.
On the morning of the fourth day the dyeing may be commenced.
The temperature should be maintained at a pretty uniform point; if it
be too hot, the blue takes a red reflection, by reason of the madder
contained in the liquid. A vat thus prepared will last three months;
we may even work it for double that period, but after the third month
it appears to lose some of its indigo.
We maintain the power of the vat by introducing every night 2¼ lbs. of
madder. Some indigo is also added twice or three times a week. These
additions are made in the evening. After the former, the vat is left
at rest for forty-two hours; with the latter only for twenty-four, at
the same time observing the precautions already indicated. At the end
of three months, or sooner when we wish to stop the working of the
vat, we exhaust the indigo; for this purpose we continue to charge it
every night for the space of a month with madder, and dip into it
white cloths, or more particularly woollen tissues, which become more
or less loaded with the indigo. We must continue this plan until these
matters take up no further color. The dippings are to be performed
twice a day at first, but once only towards the termination. Many
dyers make use of this bath for preparing a new vat, but it is better
to throw this away and make it up afresh with common water.
Indian Vat.—These vats are of more simple and of more ready
construction than the pastel or woad vats. We are to boil in water a
quantity of madder and of bran, proportioned to the weight of indigo
which we wish to employ. After two hours’ ebullition, we turn into
this bath some tartar-lees, which are also to be boiled for an hour
and a half or two hours, so as to charge the bath with whatever
soluble matter they may contain; after this ebullition the bath should
be allowed to cool, and the indigo, which has been previously ground,
is then to be introduced. Supposing that we wish to employ 21 lbs. of
indigo, the following would be the proportions used in preparing this
vat: 41 lbs. tartar-lees, 13 lbs. of madder, and 5 lbs. of bran. These
vats are usually mounted in coppers of a conical shape; a small fire
should be kept up around them, so as to maintain a moderate and
uniform heat. The indigo will usually be found dissolved at the end of
twenty-four hours, often even after twelve or fifteen hours. The
liquor has a reddish color in the new vats, and a green tint in those
which are in a working state. The frothy surface, as well as the
brilliant-colored pellicle, becomes manifested in this as in all other
preparations of a like kind.
This species of vat has to be renewed much more frequently than the
woad and pastel vats, from the indigo being more difficult to dissolve
after a certain lapse of time. A moderate heat should be maintained in
all these vats.
Potash Vat.—This species of vat is extensively employed at Elbœuf for
the dyeing of wool in the flock. It presents in all respects a perfect
analogy with the Indian vat; in fact, the action of the tartar-lee in
the latter preparation depends entirely on the carbonate of potash
which it contains. The ingredients used in the preparation of the
potash vat are bran, madder, and the subcarbonate of potash of commerce.
We obtain the deep shades in this species of vat with greater celerity
than in all others, a fact which undoubtedly depends on the greater
power which potash has of dissolving indigo than is possessed by lime.
Experience proves that the potash vat has the advantage in point of
celerity of nearly a third; but this is balanced by the inconvenience
resulting from the darker shade, which we must attribute to the large
quantity of coloring matter of the madder dissolved by the alkaline
lee, and which becomes fixed on the stuff with the indigo.
To render this vat in its most favorable state, the indigo should be
made to undergo a commencement of hydrogenation before turning it into
the mixture; for this purpose we prepare in a small copper a bath
analogous to that in the vat, to which the pounded indigo is added.
This bath is maintained for twenty-four hours at a moderate heat,
taking care to stir it from time to time. The indigo assumes a
yellowish color, becomes dissolved, and in this state is turned into
the vat; we thus avoid many delays and losses in its preparation, and
indeed it would be desirable if a similar plan were adopted with all
these compounds.
German Vat.—This vat is of nearly similar dimensions to that used for
the woad, being three times the size of the potash vat. Its diameter
is about 6½ feet, and its depth 8½ feet. Having filled the copper with
water, we are to heat it to 200° Fah.; we then add 20 pailsful of
bran, 22 lbs. of carbonate of soda, 11 lbs. of indigo, and 54 pounds
of lime, thoroughly slaked, in powder. The mixture is to be well
stirred, and then set aside for two hours; the workman should
continually watch the progress of the fermentation, moderating it more
or less by means of lime or carbonate of soda, so as to render the vat
in a working state at the end of twelve, fifteen, or, at the most,
eighteen hours. The odor is the only criterion by which the workman is
enabled to judge of the good state of the vat, he must therefore
possess considerable tact and experience.
In the process of dipping we introduce 84 lbs., 106 lbs., or even 130
lbs. of wool, in a net bag, similar to that used in the woad vat,
taking care that the bag is not allowed to rest against the sides of
the copper. When the wool has sufficiently imbibed the color, we
remove the bag containing it, and allow it to drain for a short time
over the vessel. We operate in this way on two or three quantities in
succession; we then remove the vat, and set it aside for two hours; we
must be careful, from time to time, to replace the indigo absorbed by
the wool, as also to add fresh quantities of bran, lime, and
crystallized carbonate of soda, so as constantly to maintain the
fermentation at a suitable point.
The German vat differs, then, from the potash vat by the fact that the
potash is replaced by crystallized carbonate of soda and caustic lime,
which latter substance also gives to the carbonate of soda a caustic
character. It presents a remarkable saving as compared to the potash
vat; hence the frequency of its employment; but it requires great
care, and is more difficult to manage. It also offers considerable
economy of labor; one man is amply sufficient for each vat.
The army cloth is usually dyed by means of the pastel vat, which gives
the most advantageous results. We here make use of vats about 8½ feet
in depth, and 5 feet in diameter, into which we introduce from 361
lbs. to 405 lbs of pastel or of woad, after previous maceration. The
vat is to be filled with boiling water, and we then add to the bath 22
lbs. of madder, 17½ lbs. of weld, and 13 lbs. of bran. The mixture is
to maintained in a state of ebullition for about half an hour; we next
add a few pailsful of cold water, taking care, however, not to lower
the temperature beyond 130° Fah.; during the whole of this time a
workman, provided with a rake, keeps incessantly stirring the
materials of the bath. The vat is then accurately closed by means of a
wooden lid, and surrounded by blankets, so as to keep up the heat. It
is now put aside for six hours; after this time it is again stirred by
means of a rake, for the space of half an hour; and this operation
should be repeated every three hours until the surface of the bath
becomes marked with blue veins; we then add from six to eight pounds
of slaked lime.
The color of the vat now borders on a blackish-blue. We immediately
add the indigo in a quantity proportioned to the shade which we wish
to obtain. The pastel in the foregoing mixture may last for several
months; but we must renew the indigo in proportion as it becomes
exhausted, at the same time adding both bran and madder. In general we
employ—
11 to 13 lbs. of good indigo for 100 lbs. of fine wool.
9 to 11 lbs. of good indigo for 100 lbs. of common wool.
9 to 11 lbs. of good indigo for 131 yards of cloth dyed in the piece.
Management of the Vats.—A good condition of the vat is recognized by
the following characters: The tint of the bath is of a fine
golden-yellow, and its surface is covered with a bluish froth and a
copper-colored pellicle. On dipping the rake into the bath, there
escapes bubbles of air, which should burst very slowly; when they
vanish quickly, it becomes an indication that we must add more lime.
The paste which is found at the bottom of the vat, green at the moment
of its being drawn up, should become brown in .the air; if, however,
it remains green, this is a further sign that more lime is required.
Lastly, the vat should exhale the odor of indigo. We usually complete
the assurance of the vat being in a good state by plunging into it,
after two hours’ respite, a skein of wool, which, on being withdrawn
after the lapse of half an hour, should present a green color, but
change directly to blue. We then once more mix the materials of the
vat, and two hours after it may be considered ready for dyeing.
These vats, like those already described, are provided with a large
wooden ring, the interior of which is armed with a kind of network,
for the purpose of preventing the objects which are intended to be
dyed coming in contact with the materials at the bottom of the vat;
we, moreover, take the precaution of enclosing the wool or cloth in
bags. These tissues, when plunged into the bath, should remain there
for a longer or shorter time, according to the shade which we wish to
obtain; one dipping, however, will never suffice for this object;
usually we leave in the stuff for half an hour only; it is then to be
taken from the bath, wrung, and exposed to the air. This operation is
repeated until we have succeeded in procuring the desired shade; we
ordinarily suffer three hours to elapse between each dipping. The heat
of the vat should never be allowed to fall below 130° Fah. After each
operation the bath must be well stirred, and fresh lime added;
generally speaking, a pound a day will suffice. We re-establish the
indigo about every second day. When once this vat is well mounted, and
we are careful to examine its working, we may dye from two to four
batches a day with it.
When the stuffs have acquired the desired shade, they are first to be
washed in common water, and then in a very weak solution of
hydrochloric acid (about one part in a thousand); after this they are
again rinsed in pure water.
The Indian vat is much more easily managed than the foregoing; it
presents less danger of failure, from the fact that it is quickly
exhausted, and also from the fermentative process, which is so
difficult to govern in the pastel vat; this vat not having time to
change in character. It is prepared by first introducing an equal
quantity of madder and of bran, and a triple quantity of potash; this
is to be gradually heated until it reaches a temperature of 167° Fah.,
and we then add to it the indigo, thoroughly agitating the matters for
half an hour. The vat is maintained at a temperature of 86° to 100°
Fah., by keeping it closely covered, and at the same time the mixture
is to be stirred occasionally at intervals of twelve hours. It should
by this time present a beautiful green shade, the liquor being
surmounted by a copper-colored pellicle and a purplish froth. We may
now commence the dyeing, following the same course as with the pastel
vat; but the stirrings being here repeated much more frequently than
with the other mixture, we can dye a larger quantity of wool within a
given time. When the vat ceases to give a brilliant blue, we must
altogether renew it; if it be merely weakened, we add to it a small
quantity of freshly prepared liquor containing a few pounds of potash,
and a little less bran and madder. In giving the dark and the clear
sky blues, we must be careful to employ a quantity of indigo
proportioned to the color which we wish to obtain, or, better still,
we may use the previously exhausted vat for the dark blue.
When exposed to the influence of the putrid fermentation, indigo is
decomposed and loses its color. If rendered soluble, it obeys the
impulse communicated to the azotized matters with which it is brought
into contact, although, if macerated in pure water at the ordinary
temperature, it is itself decomposed with great difficulty.
The pastel and the woad are very prone to the putrid fermentation, by
reason of the large quantity of azotized matters which they contain,
as do all the cruciferæ; they require therefore considerable care in
their employment.
When a vat is mounted, if the fermentation be allowed to continue
unchecked, after the appearance of the blue froth and the other signs
already indicated, the liquor will acquire a yellow color similar to
that of beer; the froth will become white; it will give out a stale
smell and lose its ammoniacal odor; after a few days it will turn
whitish, and exhale a smell at first similar to that of putrefied
animal substances; then it will acquire the odor of rotten eggs, and
set free sulphuretted hydrogen. The lime in the pastel and the woad
vats, and the tartar-lee and potash in the other mixtures, are used
for the purpose of preventing these accidents.
Besides the oxygenated compound, which is formed by the combination of
oxygen with the extractive matters of the plants held in digestion,
there is a production of carbonic acid which saturates the alkaline
lee, and forms a carbonate of lime in the pastel vat. We find this
attached to the sides of the vat in such quantity that the inside of
these vessels becomes incrusted with it to a considerable depth. It is
this product which dyers call the tartar of the vat; it effervesces
with acids, and gives on analysis carbonic acid, lime, and a few
particles of indigo. In the potash vat the solubility of the carbonate
of potash prevents its deposition; but it is very probable that we
have even here a formation of some carbonated products, perhaps in
part formed at the expense of the carbonic acid of the air.
The soluble extractive principle being the only matter which remains
in solution in the bath with the indigo, the lime, &c., we have formed
deposits which, varying both in their volume and in the greater or
less facility with which they are precipitated during the various
periods of fermentation, lead to a more or less considerable waste of
time. If we plunge a piece of woollen tissue into a vat which has been
recently stirred, it will acquire a dark color, and will be found
covered with brown stains which are with difficulty removed. When the
woad or paste vat has been stirred, it need be left two or three hours
only before plunging in the stuff, at least during the early months of
its working, inasmuch as the pastel, being but slightly divided and
attenuated, is readily precipitated; but when, by reason of its
extreme division, in consequence of repeated operations, it is thrown
down with less facility, the dipping should not be performed oftener
than three times in the day.
The Indian vat requires less time than the others; we may even dye
with it an hour after stirring the mixture. The potash, being soluble,
forms no precipitate; while the ligneous fibre of the madder and the
pellicles of the bran become deposited with great facility. We can
also dip with these vats much oftener than with those made by pastel
or woad.
SICKNESS OF THE WARM VAT FOR DYEING WOOL, AND ITS REMEDIES.
We have to thank that excellent practical magazine, “The American
Chemist,” for the following notes on the sicknesses of the warm vat,
by F. W. Kugler, translated from Reimann’s Färberzeintung:—
In the wool indigo vat, among the principal “sicknesses” is the
blackening of the vat, or “sharpening.” This arises from the presence
of too much lime. When “sharpened,” the liquor, instead of having a
waxy yellow color with a dense blue film on its surface, has no film;
while the liquor is a dark blackish-green, and on being stirred shows
a gray or white scum on its surface, while it emits at the same time a
pungent odor. If the vat is only slightly affected, it is sufficient
to add some bran and madder and to let it stand over night. If it has
not quite recovered by morning, it may be necessary to heat it up,
agitate it, and let it stand for a couple of hours, after which
perhaps the addition of a little lime will be necessary.
If the vat is much sharpened, it is recommended to sink in it a bag of
bran, and leave it over night, when the fermentation will have
restored the vat in a considerable degree; but it will be necessary to
add lime cautiously and by degrees, to bring it to a proper state for
working.
The theory of the souring of the vat is given. Butyric fermentation
takes place under certain circumstances, butyric acid being formed;
and hydrogen is set free, which reduces the indigo. The addition of
lime makes the vat too strongly alkaline, and sets ammonia free, which
gives the pungent odor of the soured (_verschäften_) vat.
Simultaneously the lime with the white indigo forms a difficultly
soluble compound, which settles, and thus interferes with the working
of the vat. The excess of lime must be removed, which is accomplished
by introducing bran, which causes a lactic fermentation; and the
lactic acid neutralizes the excess of lime, and destroys the lime
compound with indigo which had been formed. The lime may be
neutralized by the use of mineral acids, but there is danger in that
case of precipitating the indigo.
A second “sickness” is “becoming too sweet.” The symptoms are,—the
blue veins and surface film disappear on stirring, the foam gives a
rustling sound, the bath assumes a reddish-yellow color, blue goods
placed in the bath lose their color, and the vat has an unpleasant odor.
The vat when “too sweet” needs to be brought to the regular
temperature, and lime to be added cautiously until the vat is brought
to its normal state. It is safer to add an excess of lime and “sour”
the vat, and then bring it back according to the directions under that
head, than to add too little, as less indigo is lost. To use up all
the dye and to dye a light blue, as little lime should be present as
is consistent with the workings of the vat.
The cause of the “falling away” of the vat is a too active
fermentation, which produces considerable lactic acid, from which
butyric acid forms, setting free hydrogen, thereby making white
indigo, which, if the action is allowed to continue, changes to a
compound from which the indigo cannot be recovered. If lime is added,
the lactic and butyric acids unite with it and precipitate it, while
the excess precipitates the white indigo, which is slowly recovered,
as fermentation progresses, which forms lactic acid, which, taking the
place of the white indigo, sets it free. Besides the sicknesses, there
are various results of mismanagement, of which the first is
overwarming, which causes the bath to turn brown, which is the
beginning of the souring.
When the bath begins to sour from overheating, some logwood should be
added and then bran, and the vat left to itself over night. The reason
of it is that the temperature is too high for the desired fermentation
to operate. The vat sometimes suddenly turns green, and even when
indigo and the other necessary ingredients are added it remains of
this color. This is called the “breaking up of the vat.” The reason is
that the temperature is too low; to remedy it, it is necessary to add
logwood and bran, warm it up, and stir, when it should stand for some