Several sulphurets, such as those of arsenic, lead, copper, antimony,
tin, are susceptible of being applied to stuffs, and of dyeing them in a
more or less fast manner. Indigo, hematine, breziline, carmine, and the
peculiar colouring principles of many dyes belong to this division.
7. Mutual action of goods with one or more definite compounds, and
dye-stuffs.
I shall consider here in a theoretical point of view, the most general
results which a certain number of organic colouring matters present,
when applied upon stuffs by the dyer.
_Indigo._ This dye-drug, when tolerably good, contains half its weight
of indigotine. The cold vat is prepared commonly with water, copperas,
indigo, lime, or sometimes carbonate of soda, and is used almost
exclusively for cotton and linen; immersion in acidulated water is
occasionally had recourse to for removing a little oxide of iron which
attaches itself to the cloth dyed in this vat.
The indigo vat for wool and silk is mounted exclusively with indigo,
good potashes of commerce, madder and bran. In this vat, the immediate
principles with base of carbon and hydrogen, such as the extracts of
madder and bran, perform the disoxidizing function of the copperas in
the cold vat. The pastel vats require most skill and experience, in
consequence of their complexity. The greatest difficulty occurs in
keeping them in a good condition, because they vary progressively as the
dyeing goes on, by the abstraction of the indigotine, and the
modification of the fermentable matter employed to disoxygenate the
indigo. The alkaline matter also changes by the action of the air. By
the successive additions of indigo, alkali, &c., this vat becomes very
difficult to manage with profit and success. The great affair of the
dyer is the proper addition of lime; too much or too little being
equally injurious.
Sulphate of indigo or Saxon blue is used also to dye silk and wool. If
the wools be ill sorted it will show their differences by the
inequalities of the dye. Wool dyed in this bath put into water saturated
with sulphuretted hydrogen, becomes soon colourless, owing to the
disoxygenation of the indigo. The woollen cloth when exposed to the air
for some time, resumes its blue colour, but not so intensely as before.
The properties of hematine explain the mode of using logwood. When
stuffs are dyed in the infusion or decoction of this wood, under the
influence of a base which acts upon the hematine in the manner of an
alkali, a blue dye bordering upon violet is obtained. Such is the
process for dyeing cotton and wool a logwood blue by means of verdigris,
crystallized acetate of copper, and acetate of alumina.
When we dye a stuff yellow, red, or orange, we have always bright tints;
with blue we may have a very dark shade, but somewhat violet; the proper
black can be obtained only by using the three colours, blue, red, and
yellow, in proper proportions. Hence we can explain how the tints of
yellow, red, orange, blue, green, and violet, may be browned, by
applying to them one or two colours which along with themselves would
produce black; and also we may explain the nature of that variety of
blacks and grays which seems to be indefinite. Nutgalls and sulphate of
iron, so frequently employed for the black dye, give only a violet or
bluish gray. The pyrolignite of iron, which contains a brown
empyreumatic matter, gives to stuffs a brown tint, bordering upon
greenish yellow in the pale hues, and to chestnut brown in the dark
ones. By galling cotton and silk, and giving them a bath of pyrolignite
of iron, we may after some alternations dye them black. Galls, logwood,
and a salt of iron, produce merely a very deep violet blue; but by
boiling and exposure to air, the hematate of iron is changed, becoming
red-brown, and favours the production of black. Galls and salts of
copper dye stuffs an olive drab, logwood and salts of copper a violet
blue; hence their combination should produce a black. In using sumach as
a substitute for galls, we should take into account the proportion of
yellow matter it contains. When the best possible black is wanted upon
wool, we must give the stuff a foundation of indigo, then pass it into a
bath of logwood, sumach, and proto-sulphate of iron. The sumach may be
replaced by one third of its weight of nutgalls.
8. Of dyed stuffs considered in reference to the fastness of their
colours, when exposed to water, light, heat, air, oxygen, boiling and
reagents.
Pure water without air has no action upon any properly dyed stuff.
Heat favours the action of certain oxygenized bodies upon the
carbonaceous and hydrogenous constituents of the stuff; as is seen with
regard to chromic acid, and peroxide of manganese upon cotton goods. It
promotes the solvent action of water, and it even affects some colours.
Thus Prussian blue applied to silk, is reduced to peroxide of iron by
long boiling.
Light without contact of air affects very few dyes.
Oxygen, especially in the nascent state, is very powerful upon dyes. See
BLEACHING.
The atmosphere in a somewhat moist state affects many dyes, at an
elevated temperature. Silk dyed pink, with safflower, when heated to
400° F. becomes of a dirty white hue in the course of an hour. The
violet of logwood upon alumed wool becomes of a dull brown at the same
temperature in the same time. But both stand a heat of 300° F. Brazil
red dye, turmeric, and weld yellow dyes display the same phenomena.
These facts shew the great fixity of colours commonly deemed tender. The
stuffs become affected to a certain degree, under the same circumstances
as the dyes. The alterability even of indigo in the air is shewn in the
wearing of pale blue clothes; in the dark blue cloth there is such a
body of colour, that it resists proportionally longer; but the seams of
coats exhibit the effect very distinctly. In silk window curtains, which
have been long exposed to the air and light, the stuff is found to be
decomposed as well as the colour.
_Boiling_ was formerly prescribed in France as a test of fast dyes. It
consisted in putting a sample of the dyed goods in boiling water,
holding in solution a determinate quantity of alum, tartar, soap, and
vinegar, &c. Dufay improved that barbarous test. He considered that
fast-dyed cloth could be recognized by resisting an exposure of twelve
hours to the sunshine of summer, and to the midnight dews; or of sixteen
days in winter.