RECIPES FOR BLACKBOARD SLATING.
Dissolve 1 pound shellac in 1 gallon 95 per cent. alcohol; then add ½ pound best powdered ivory black, 5 ounces finest emery flour, 2 ounces ultramarine blue; mix well and keep air tight. When using stir frequently. If thick enough to show brush marks, add more alcohol; work quick with a fine brush.