12 ounces of hydrate of protoxide of tin, obtained by precipitating it from the muriate of tin by solution of potash.
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.
10. Topical grounding blue for the cylinder press.
Take 31⁄2 gallons of caustic soda lye of spec. grav. 1·15.
Take 31⁄2 lbs. of ground indigo.
Take 5 lbs. of precipitated protoxide of tin (as above).
Boil the mixed ingredients for ten minutes, take them from the fire, and add, first, 3 lbs. of Venice turpentine; then 11 lbs. of gum.
Put this mixture into the colour trough, print with it, and after two days wash in the dash-wheel; then pass it through a soap bath, along with a little soda, to brighten the blue, and to take off its greyish tint.
The use of the turpentine is easily explained; it serves to exclude the atmospherical oxygen, and prevent the regeneration of the indigo blue, before it is spread upon the cloth.
After the application to white calico of a similar blue, into which a little acid muriate of tin has been put, the goods are dipped for ten minutes in thin milk of lime, shaking the frame all the time. They are then washed, and cleared with a soap boil. The following colour remains long in the deoxidized state from its containing 8 ounces of indigo, 10 ounces of hydrated protoxide of tin, and 11⁄2 pounds of solution of muriate of tin, to 2 quarts of soda lye of 1·15, thickened with 21⁄2 pounds of gum. This blue may be applied by either the block or the cylinder.