1. Wheat starch.
2. Flour.
3. Roasted starch.
4. Gum senegal.
5. Gum tragacanth.
6. Salep.
7. Pipe-clay, mixed with gum senegal.
8. Sulphate of lead.
9. Sugar.
10. Molasses.
11. Glue.
After thickening with gum, we ought to avoid adding metallic solutions
in the liquid state; such as nitrate of iron, of copper, solutions of
tin, of subacetate of lead, &c.; as they possess the property of
coagulating gum. I shall take care to specify the nature and proportion
of thickening to be employed for each colour; a most important matter,
hitherto neglected by English writers upon calico printing.
The atmosphere of the printing shops should never be allowed to cool
under 65° or 70° F.; and it should be heated by proper stoves in cold
weather, but not rendered too dry. The temperature and moisture should
therefore both be regulated with the aid of thermometers and
hygrometers, as they exercise a great influence upon all the printing
processes, and especially upon the combination of the mordant with the
cloth. In the course of the desiccation, a portion of the acetic acid
evaporates with the water, and subacetates are formed, which combine
with the stuff in proportion as the solvent principle escapes; the water
as it evaporates carries off acetic acid with it, and thereby aids the
fixation of bases. These remarks are peculiarly appropriate to delicate
impressions by the cylinder machine, where the printing and drying are
both rapidly effected. In the lapis lazuli style, the strong mordants
are apt to produce patches, being thickened with pipe-clay and gum,
which obstruct the evaporation of the acids. They are therefore apt to
remain, and to dissolve a portion of the mordants at their immersion in
the blue vat, or at any rate, in the dung bath. In such a case a hot and
humid air is indispensable, after the application of the mordants; and
sometimes the stuffs so impregnated, must be suspended in a damp
chamber. To prevent the resist pastes becoming rapidly crusty,
substances apparently useless are mixed with them, but which act
beneficially by their hygrometric qualities, in retarding the
desiccation. Oil also is sometimes added with that view.
It is often observed that goods printed upon the same day, and with the
same mordant, exhibit inequalities in their tints. Sometimes the colour
is strong and decided in one part of the piece, while it is dull and
meagre in another. The latter has been printed in too dry an atmosphere.
In such circumstances a neutral mordant answers best, especially if the
goods be dried in a hot flue, through which humid vapours are in
constant circulation.
In padding, where the whole surface of the calico is imbued with
mordant, the drying apartment or flue, in which a great many pieces are
exposed at once, should be so constructed as to afford a ready outlet to
the aqueous and acid exhalations. The cloth ought to be introduced into
it in a distended state; because the acetic acid may accumulate in the
foldings, and dissolve out the earthy or metallic base of the mordant,
causing white and gray spots in such parts of the printed goods. Fans
may be employed with great advantage, combined with HOT FLUES. (See this
article.)
In the colour laboratory, all the decoctions requisite for the print
work should be ready prepared. They are best made by a steam heat, by
means of copper boilers of a cylindric form, rounded at the bottom, and
encased within a cast-iron cylinder, the steam being supplied to the
space between the two vessels, and the dye-stuff and water being
introduced into the interior one, which for some delicate purposes may
be made of tin, or copper tinned inside. A range of such steam apparatus
should be placed either along one of the side walls, or in the middle
line of the laboratory. Proper tables, drawers, phials, with chemical
reagents, measures, balances, &c., should also be provided. The most
useful dye-extracts are the following:--
Decoction of logwood, of Brazil wood, of Persian berries, of quercitron
bark, of nut-galls, of old fustic, of archil or cutbear, of cochineal,
of cochineal with ammonia, of catechu.