DIRECT COTTON OR SALT COLORS
Among the many changes made in the art of dyeing since the
introduction of the coal-tar dyestuffs, perhaps the most important
has been the gradual overcoming of the necessity for mordanting the
textiles before coloring them in the dye-bath. Almost all of the old
vegetable dyes were mordant dyes; that is, the color could not be
fastened to the fibre, whether wool, cotton, linen, or even silk,
unless the latter had been impregnated with some chemical which would
act as a _mordant_ to—(i.e., would combine with and hold) the color.
These mordants were, in general, the salts of some metal, aluminium,
tin, chromium, and iron salts being the ones in common use; and the
processes involved in properly mordanting the goods were in many
cases—notably in the case of madder and the Turkey red process—far
more difficult and tedious and expensive than the actual dyeing.
The first dyestuffs discovered, the true aniline dyes, which were
manufactured directly from aniline and from substances strongly
resembling aniline in chemical composition, were at once found to
act in a different manner on textile fibres. Animal fibres like wool
and silk, fur and leather, were dyed by them directly, without the
use of any mordant at all. If the dyestuff were dissolved in water
(the addition of a little acid makes the color dissolve more readily,
but is without other effect) and a wet skein of wool or silk were
immersed in it, and a little heat applied, the color would leave the
liquid, and fasten itself firmly on to the goods.
But with cotton and linen and other vegetable fibres, these dyes
would not work so well. When these materials are warmed in such a
dye-bath, the color does not adhere to the fibres, but washes off
directly in a hot soap bath, if not, indeed, under a stream of clear
hot water. This was noticed by Perkin very soon after his famous
discovery, and, wishing to use his new color for dyeing cotton and
linen as well as silk and wool, he set to work to discover how to
prepare these materials; in short, how to mordant them so that they
too would take firm hold of the color. As will be described later
in the chapter on Basic colors, his experiments soon led to the
introduction and the use of tannic acid and tartar emetic combined,
in a process widely used to this day.
The next class of dyestuffs discovered were the so-called acid
colors, thus named because they all exhibited distinctly acid
properties—that is, they would form salts with the substances known
as bases (of which last, by the way, aniline is an important member).
These colors, like the earlier ones, would dye the animal fibres
directly, but would not color the vegetable fibres, unless the
latter were carefully mordanted with alumina, or iron oxide, or some
similar metallic base. And even this treatment does not give colors
that are fast to washing, so these acid colors are never used on
cotton or linen.
After this came the discovery of alizarine, and an important series
of very fast and very valuable dyes, all of which were characteristic
mordant colors. Even wool and silk, as well as every other textile,
must be carefully mordanted with aluminium, chromium, or iron
salts, in order to have any coloring effect produced by these
dyestuffs. This is the chief reason why, in spite of their beauty
and great permanence, the alizarine and other mordant colors are
being less used every year. At the end of some twelve or thirteen
years after the discovery of the aniline colors, therefore, it was
still impossible to dye cotton with them without a more or less
elaborate mordanting process. And yet the problem did not seem to be
an impossible one. One of the natural dyes, the safflower, already
mentioned, has the property of dyeing cotton pretty, and not very
fugitive, shades of pink and rose colors, directly, without the
necessity for any mordant; and if a natural dyestuff could do that
why could not some artificial ones?
Some thirty years ago, a chemist (one story says that it was a
laboratory boy) while experimenting with a dyestuff which was then
a recent discovery—Congo red, a very brilliant but fugitive and
unstable scarlet color—noticed that while filtering a hot solution
of it through filter paper, the paper was stained deeply, and, which
was more important, the color was not easily washed out with hot
water. This excited his curiosity, and after following the matter
up a little, he found that not only this Congo red, but a whole
series of dyestuffs formed in the same general way, had the power of
dyeing cotton directly. This discovery has practically revolutionized
the whole art of cotton dyeing. From these few bright and pretty,
but distinctly untrustworthy dyes, which were at once named and
advertised as “direct cotton colors,” have sprung great numbers of
dyestuffs—several hundreds at least—of every conceivable shade, and
of late years of every conceivable degree of fastness to light.
All resemble the original Congo red in that they will dye cotton
and linen, if not absolutely fast, at any rate very fairly fast to
washing, in one bath, without the need of any mordants.
This, of course, means that the cost of dyeing cloth with these
dyes is very much less than with the other classes mentioned. And,
by the way, it also explains why, under the name of Turkey red,
so many extremely bad colors have been sold. To dye Turkey red on
cotton, using alizarine, and with the most improved and simplified
methods, necessitates at least six or seven different steps, each
of which requires not only time and expense, but great skill and
care; and any one of them, if carelessly performed, may spoil the
goods. On the other hand, a mere beginner, by using one of the
early, bright, direct colors (quite cheap in itself, because the
patents have expired) can, by boiling the goods for half an hour in a
dye-bath with a little soap and salt in it, produce a piece of cloth
dyed almost the exact shade of the old Turkey red, for probably
one-third, or one-quarter of the price. It will look the same on the
shop counter; will probably sell just as well to the average, or even
to the painstaking customer; but when exposed to air and light for a
few weeks, perhaps even for a few days, will lose its brilliancy, and
turn some queer, dull shade, probably of purple.
Indeed this particular substitution has been going on for some
years on a large scale; and at one time promised to be of some
international importance. The Turkey red dyers in Manchester, a few
years ago, complained bitterly to the English Government that their
market in India was falling off very seriously; and they demanded an
investigation, to know what was the matter.
After careful inquiry by the local officials, word came back that
there was no difference in the taste of the people for bright scarlet
clothes and headgear. Just as much red was worn as ever before. But
active agents of the large German color houses had been going through
the country, introducing some of these cheap direct cotton scarlets
and showing the natives how to use them. And in consequence, up and
down India in all the little towns, even in the villages, local dyers
were at work who, for a few cents, would dye up an old piece of
calico bright red. When it became faded again in a few weeks, they
would dye it over again for a very small sum, thus renewing the same
piece whenever it was desirable to appear in bright, new clothes.
_Names._—These dyes have long been made by all of the great firms,
although two or three have made more of a specialty of them than the
rest. It was soon found that the presence of common (table) salt in
the dyestuffs was valuable, as lessening the waste of dyestuff in the
dye-liquor, and also increasing the fastness to washing of the dyed
goods. For this reason the common name given to this class is that of
“Salt Colors.” Owing, however, to the fact that Congo red, the first
discovered of the whole class, was derived from the chemical known as
benzidine, these salt colors are sometimes referred to, in general,
as the “Congo,” or as the “benzidine” dyes. Besides this they are
frequently known as “cotton colors,” or “direct cotton colors.” The
different manufacturers, however, have assigned certain class names
to their own dyestuffs, as follows:
Benzo (_Elberfeld_); Diamine (_Cassella_); Dianil (_Metz_);
Mikado (_Elberfeld_); Naphthamine (_Kalle_);
Oxamine (_Badische_); Phenamine (_Badische_).
_Uses._—These colors are chiefly used for dyeing cotton, linen,
and paper. They take particularly well on mercerized cotton, and
on some varieties of artificial silk. They can also be used to dye
wool and silk, and, indeed, in many cases give colors faster, both
to light and to washing, on these fibres than on cotton. As a rule
they will not dye animal fibres excepting at a high temperature—near
the boiling point—and in an acid bath. Whereas cotton and linen are
preferably dyed in an alkaline or at least a neutral bath, and, while
they must be boiled in the dye-bath for at all permanent results,
will take the color as a stain at quite low temperatures.
For this reason these dyes are often used for dyeing even shades in
one bath, upon mixed goods—that is, wool and cotton, cotton and silk,
etc. The goods are first dyed in a lukewarm bath till the cotton is
nearly the proper shade, and then, on heating, the wool or silk will
take up the color and, before long, catch up with the cotton. It
must, however, be remembered that on cotton and linen these dyes are
not, as a rule, at all fast to washing, unless they have been well
boiled with the goods. When dyed on silk at a boil, they are fast to
hot soap and water, a fact which, sometimes, is of much importance.
DYEING DIRECTIONS
=Dye-bath.=—The color must first be dissolved in water, care being
taken not to leave any undissolved lumps or specks of color floating
around in, or settled at the bottom of, the dye-bath. For this
reason it is generally best, in all dyeing operations, first of all
to make a decidedly strong solution of the color, by dissolving a
considerable quantity of it (depending of course on the amount of
goods to be dyed) in hot water, in a pitcher or saucepan. In the
dyehouse this would be called a “stock solution,” and would always be
made of a definite strength,—say five parts of color to one hundred
of water—and kept well covered up. Sometimes in hot weather it would
be treated with a little preservative like benzoate of soda, so that
it could be used at any time it was needed. When this color solution
is added to the dye-bath, it should always be carefully strained
through a piece of cheesecloth or any other fine medium that will
catch the specks and undissolved lumps. Otherwise spots are liable
to appear, on the finished goods, which it is almost impossible to
eradicate without stripping off every trace of color from the dyed
material.
_Water._—The dye-bath is prepared with plain water. The amount
necessary for each lot of goods can only be told by experience. For
some classes of dyes, like the Acid colors and the Basic colors,
to be described later, the quantity of water makes but little
difference. But for dark shades with these Salt colors it is best not
to have more than enough water to thoroughly soak, and comfortably
cover, the wetted goods, with enough room to stir and turn them
easily. The dye-bath is now set on the stove to warm up and, when
dyeing light or medium shades, some soap is usually dissolved in it.
This is not absolutely necessary but helps to make the color go on
more evenly, and penetrate the fibres better.
_Soap._—For dyeing purposes in general, any pure, carefully made
soap acts satisfactorily. For silk dyeing, and especially for silk
finishing, it is said that greater lustre can be gained with olive
oil (Castile) soap. But when this cannot be obtained, Ivory soap or
Pears’ soap or, in fact, any good brand of bath or toilet soap will
do almost as well. For the washing and finishing of wool and silk the
use of strong laundry soaps should be avoided if possible, because
they usually contain alkali, in the form of borax or of carbonate
of soda, which is liable to “tender the goods.” For cotton and linen
dyeing and finishing, this does not make any difference. The easiest
way to add the soap to the dye-bath is to use it in one of the wire
soap-shakers, which has a convenient handle, and holds half a cake or
even a whole cake of soap at one time.
=Even Dyeing.=—The goods should be well washed, rinsed, and wrung
out, so as to be sure that they are free from dirt and grease, and
have been thoroughly and evenly wet. They are then placed in the
dye-bath, completely under the liquid, and stirred round and round
and turned over and over with the dye-sticks. The chief objects in
stirring are, first, to prevent part of the goods from resting on
the bottom and then getting more heat than the rest of the material,
in which case, naturally, it will become darker when finished; and
second, to prevent the outside portion of the goods from getting more
color than the inner portions. Accordingly the goods, when placed in
the dye-bath, must be well opened up and, excepting when deliberately
making patterns by the method described later under the name of
“Tied and Dyed Work,” they should not be tied or entangled in knots
or bunches. Every part must be equally exposed, by the turning and
lifting and stirring, to the action of the color solution.
If only light shades are desired, the goods are heated and turned
until the proper shade has been reached—remembering always that,
unless the color has been boiled on, it is likely to be only a stain
which will wash off easily.
_Salt._—For full and indeed for medium shades, it is customary to
add to the dye-bath some agent—usually table salt or, when the shade
is not very dark, phosphate of soda—which will make the color less
soluble in the dye-liquor and will tend to throw it on the fibre.
For, after all, there is comparatively little affinity between the
cotton fibre and the dyestuff (far less than between silk or wool
and the Acid or Basic colors), and when a skein is warmed or even
boiled in the dye-bath a large proportion of the color remains in the
liquid. The bath is not “exhausted” as the dyers say. Hence, if we
try to dye full shades with these colors dissolved in water only, or
in soap and water, it can only be done by using large quantities of
the dyestuff, most of which will be wasted in the spent dye-liquor.
For dark shades, then, where there is little danger of uneven dyeing,
the goods are usually dyed for a short time with the color dissolved
in hot water. And then, to deepen the shade, the goods are lifted,
and common salt added in considerable quantities, three or four
tablespoonfuls to the gallon, and stirred round till it is dissolved.
Then the goods are put back and well boiled for half an hour or so,
before the dyeing is considered complete. The presence of salt, by
increasing the temperature of the boiling bath, also helps to make
the dyed goods fast to washing.
Soap cannot be used in the presence of so much salt for fear of its
depositing on the fibre in spots and so causing trouble. For medium
shades, however, where it is well to use soap in the dye-bath so
as to have the color go on the fibre evenly, a little phosphate of
soda is often employed instead of salt, one or two tablespoonfuls to
the gallon, to diminish the waste of color, without making the soap
insoluble.
For the darker shades it is particularly important to thoroughly boil
the goods for half an hour or more, before taking them out of the
dye-bath. Otherwise the dyestuff will not penetrate the fibre, but
will simply stain the surface, and will not only be easily washed
off, with very mild soaping, but, when dry, will be apt to crack and
rub.
_Finishing._—After the materials have been dyed as just described,
they should be taken out of the dye-bath, rinsed with water to wash
off the excess of dye-liquor, and then shaken out and dried.
When used in this way the best dyes of this class, such as those
listed a little further on, will give, on cotton and linen, shades
that are very fast to light, and fairly fast to washing. On wool and
silk the shades are fast to both light and washing. For purposes of
comparison it may be stated here what is generally meant by these
terms.
_Fastness to Light._—The test for light-fastness is usually made by
partially covering a dyed skein with a piece of wood, or heavy piece
of blotting paper, and exposing it to direct sunlight, back of a
window with southern exposure. At intervals the skein is taken out
and the color studied, and it is then easy to see whether any change
has taken place in the portion of the goods exposed to the light.
If the goods have faded appreciably in the space of one week, the
dyestuff is considered _not fast_.
If the color changes after two weeks’ exposure, but not after one
week, it is to be considered _fairly fast_.
If it stands for two weeks but fades in four weeks it is to be called
_fast_.
And if it resists, without appreciable change, the action of the
summer sunlight for full four weeks, it is called _very fast_.
It should be remembered, in this connection, that the comparative
fastness to light depends largely (a) upon the materials to be dyed,
and (b) upon the depth and shade of color used in the test. For
instance, if a skein of heavy cotton yarn, and one of very fine,
brilliant, artificial silk are dyed the same color, and exposed to
light under the same conditions, the cotton skein will hold its
color longer than the silk. The latter, being semi-transparent,
allows the sunlight to pierce it through and through, while the more
opaque cotton gives some distinct protection to the color that has
penetrated beneath the surface. So, too, a dark shade of any given
color will stand the light much better than a very light or delicate
shade, for the same general reason. The color beneath the surface is
protected from the direct action of the sun’s rays by the surface
color.
_Fastness to Washing._—The test for washing-fastness is made somewhat
differently. A skein dyed a full shade with the color is twisted up
with two white skeins, one of wool and the other of cotton, and
the three are thoroughly scoured for ten minutes in a strong bath
of good quality laundry soap, heated to 140°F. This temperature is
uncomfortably hot for the hands and yet is well below the boiling
point. A _fast_ color is one where, with this treatment, neither the
soap liquor nor either one of the skeins becomes colored.
If the soap liquor is colored but neither one of the skeins, the dye
is called _fairly fast_.
If the soap bath is tinged, and one or the other of the skeins
becomes colored at the same time, the dye is considered _not fast_.
It must, however, be borne in mind that before making this
washing-test, all excess of dye-liquor must first be removed by
thorough rinsing. And it should be remembered that even the fastest
of the Salt colors, as well as of the Acid and Basic colors described
later, when applied directly to the fibre, without mordanting or
after-treating, are never as fast to washing as those where the
dyestuff is fixed or developed in an insoluble form in the fibre,
by the action of the air, as are the Sulphur and Vat colors—or
by the action of mordants, as with the Alizarine colors—or by
after-treatment with certain special chemicals, as with the Salt
colors in the process described below. All dyes can, sooner or later,
be dissociated from the fibres to which they are attached. But if
they are in an insoluble condition they drop off in the form of a
powder, and are washed clean off, and leave sharp, clear outlines
on the dyed goods. If, however, they have gone on in solution
they will go off in solution, and are liable to _bleed_, and stain
light-colored fibres near them.
The earlier dyestuffs of this class were deservedly criticised as
being, even when carefully applied, much given to bleeding, and also
distinctly fugitive to the action of sunlight.
Of late years the quality of these dyestuffs has greatly improved,
and the best of them, like those mentioned below, when carefully dyed
on cotton, are fast, if not very fast to light, although for washing
the very best can hardly be classed even as fairly fast, without
after-treatment.
_List of Selected Dyestuffs._—
Badische— Oxamine Fast Red, F
Cotton, Yellow, G I
Stilbene Yellow, G K
Oxamine Blue, B
Cotton Black, E, extra
Cassella— Diamine Fast Red, F
Diamine Fast Yellow, G G
Diamine Fast Blue, F F G
Diamine Fast Black, F
Elberfeld— Benzo Fast Red, 8 B L
Benzo Fast Yellow, 4 B
Brilliant Fast Black, 4 B
Pluto Black, F, extra
Kalle— Naphthamine Fast Red, H
Naphthamine Fast Yellow, 2 G L
Naphthamine Fast Blue, 4 B L
Naphthamine Fast Violet, R L
Naphthamine Direct Black
Metz— Dianil Fast Scarlet, 4 B S
Dianil Orange, G
Dianil Yellow, O O
Dianil Fast Blue, 3 B
Dianil Fast Black, conc.
As above mentioned, even the very best dyes belonging to this class
of Salt colors, give on cotton and linen results only “fairly fast”
to washing. As the modern laundress is not averse to using stronger
agents than good laundry soap in her washtub, and not infrequently
indulges in considerable amounts of washing soda (sodium carbonate)
and even of bleaching powder, to clean quickly a dirty piece of
goods, dyes that are “fairly fast” according to the regular standard,
will, in practice, need some care spent on them if they are to hold
their color for long periods. Against light the best ones are almost
as fast as any dyes known, but none of them are a match for the
Sulphur colors, or especially the Vat colors, when exposed to severe
washing.
_After-treatment._—The professional dyer, who is occasionally
called upon to produce fast colors with these dyes, and even with
the inferior members of this class, has found various methods of
after-treatment, by which the colors are rendered more permanent.
A favorite process, where the dyer is enough of a chemist to carry
it out, consists of making an entirely new dyestuff in the fibre,
generally of an entirely different shade, and with much greater power
of resistance to washing and to light, by treating the dyed goods
first with a mixture of sodium nitrite and of sulphuric acid, and,
after this, passing them through a solution of some organic chemical
such as carbolic acid, alpha- or beta-naphthol, or others known as
developers.
This process, known as “diazotizing and developing,” is considerably
used in the trade, especially for various shades of black, but is too
complicated and delicate for craftsmen in general.
A simpler process is to warm the dyed goods for five or ten minutes
in a weak solution of the orange-colored salt, bichromate of potash,
acidified with a little acetic acid—or of the not uncommon chemical,
sulphate of copper, long known to chemists as blue vitriol.
When the best dyes are used, like those in the preceding list, it
is not often necessary to use either of these reagents. But when,
as sometimes happens, one is obliged to use dyes of this general
class, bought at the country store without a chance of knowing how
fast they are, it is well to know about it. For a piece of goods the
size of an ordinary linen skirt, the after-treating bath would be
made as follows: In two and a half gallons of hot water, dissolve two
tablespoonfuls of sulphate of copper, one tablespoonful of bichromate
of potash, and two teaspoonfuls of ordinary acetic acid (equivalent,
say, to three or four teaspoonfuls of strong vinegar). The goods,
after dyeing and rinsing, but before drying, should be soaked in this
bath and heated for ten minutes until not far from the boiling point.
They should then be taken out, rinsed carefully, and dried. This
after-treatment does not benefit every single color of this class,
but it helps greatly the fastness to light and to washing of almost
all of them. The chief objection to it, besides the time and expense,
is that the shade of the finished goods is often considerably
changed by the process.
_Properties and Uses of the Salt Colors._—Generally speaking, the
shades produced by the individual members of this group cover all
the colors of the rainbow and include several good greys. It is
hard, however, to get a full deep black on cotton or linen with
these dyes, without using the “diazotizing and developing” process
of after-treatment. The dyes go on the fibre in a soluble form, and
unless a developing process like this is used they combine directly
with the fibre, and do not form a coating or layer upon it, as do
some of the “developed” dyestuffs. Accordingly, no matter how fully
or how deeply we dye a piece of yarn or cloth with a black dye of
this class, the finished goods will show _grey_, a very dark grey,
to be sure, but still grey, and not a flat, heavy, true black. The
color of most of the salt blacks is greatly improved, however—as well
as their fastness to light and washing—by soaking the dyed goods,
after rinsing, in a solution containing four or five spoonfuls of
formaldehyde to the gallon.
This same property, however, of combining directly with the fibre,
makes the colors brighter and more brilliant than many of the other
classes, especially in the lighter shades. Accordingly for bright,
pretty shades of pinks, blues, yellows, and of mixed shades, fast to
light, but not very fast to washing, very easily and simply applied,
these colors are extremely valuable. For instance, in dyeing large
quantities of bright colors on calico or cheesecloth, for some
special occasion, as a pageant or spectacle, these are the colors to
use.
Another great advantage they possess is that they dye true; that is,
they do not alter their color when exposed to the air, and the color
of the finished goods can be fairly estimated from the color of the
dye-bath.
Accordingly, the student is strongly urged to practise the art
of dyeing with these colors. They are cheap and can be readily
obtained, although not always of the very best quality, under the
name of Diamond Dyes for cotton, ezy dyes, etc., from druggists and
grocerymen all over the country.
They can be easily applied to cheesecloth, muslin, and other
inexpensive materials, and if care is taken to soak and boil the
goods thoroughly, to linens and heavy cottons. In case of necessity
they can be used on wool and silk, but, as a rule, their use is
limited to vegetable fibres. They are particularly valuable to
amateur dyers and to beginners in the art, because they have great
“levelling” power; that is, it is easy to dye evenly with them.
On the other hand, it is a nuisance, oftentimes, to have to boil the
goods, and even then the colors are not really fast to washing. At
any rate, before proceeding to the study of the more permanent but
more complicated Sulphur and Vat colors, the art of dyeing even and
rainbow shades and at least the beginnings of the art of combining
and matching shades should be carefully and conscientiously worked
out with these often despised, but really very useful and valuable,
Salt colors.