Take half a gallon of water of 120° F., 8 ounces of ground indigo, and 8
ounces of red sulphuret of arsenic (orpiment), 8 ounces of quicklime,
mix together, and heat the mixture to the boiling point; withdraw from
the fire, and add, when it is lukewarm, 6 ounces of carbonate of soda,
stir and leave the whole at rest till the next day. Then decant the
clear liquor, and thicken every quart of it with half a pound of gum.
This colour ought to be green, and be preserved in a close vessel. When
used it is put into a pot with a narrow orifice, the pencil is dipped
into it, wiped on the edge of the pot, and immediately applied by hand.
This plan is tedious, and is nearly superseded by the following
grounding blue.
Take half a gallon of caustic soda lye of spec. grav. 1·15, heated to
120° F.
12 ounces of hydrate of protoxide of tin, obtained by precipitating it
from the muriate of tin by solution of potash.
[Illustration: 236 237]
8 ounces of ground indigo; heat these mixed ingredients to the boiling
point, then move the pot off and on the fire two or three times in
succession, and finally thicken, with 3 pounds of raw sugar. In order to
apply this by the block, the following apparatus is employed, called the
_canvass frame_; _figs._ 236. 237. It is formed of a copper case or box
A, in which is laid a frame B, filled with pretty stout canvass. The box
communicates by a tube with the cistern C, mounted with a stop-cock D.
_Fig._ 237. represents the apparatus in plan: A, the box; B, the
canvass, with its edges _a a a a_, fixed by pin points to the sides. The
colour is _teared_ (_tiré_), or spread even, with a wooden scraper as
broad as the canvass. In working with this apparatus, the colour being
contained in the vessel C is drawn off into the case A, by opening the
stop-cock D, till it rises to the level of the canvass. The instant
before the printer daubs the block upon the canvass, the _tearer_
(_tireur_), boy or girl, runs the scraper across it to renew its
surface; and the printer immediately transfers the colour to the cloth.
In this kind of printing great skill is required to give evenly
impressions. As the blue is usually applied to somewhat large designs,
it is very apt to run; an inconvenience counteracted by dusting fine dry
sand upon the cloth as soon as it is blocked. The goods must be washed
within 24 hours after being printed.