Blackboard Slating Liquid can be made in several ways. When it is desired in such form, that after the application of several coats the board may be written on with soapstone pencils, the following formula will answer:
In a suitable apparatus, mix 3 pounds drop black and 1/2 pound ultramarine blue, both ground in oil with 3 1/2 pounds washed emery flour and 12 lbs. coach japan, preferably made on a gum shellac base and when well beaten up, thin with 6 pounds gum spirits of turpentine, strain through a fine sieve and put up in well sealed cans or jars. The yield of this batch will be 2 1/2 gallons.
Another formula, which however will not produce a slating for pencils, but a very good one for school crayons, is as follows:
Take enough from one gallon of denatured alcohol to triturate 3 ounces dry lampblack and 5 ounces dry ultramarine blue. In the balance of the alcohol, dissolve one pound orange shellac; add to this the triturated black and blue, also 1/2 pound rotten stone and 3/4 pound pumice stone both in fine powder, mix well, strain and bottle.