To make black crayons, mix 10 parts of pipeclay, 1 to 1 1/2 parts of lampblack, and 1 part of Prussian blue with water to a stiff paste. Well knead all the ingredients together. Allow the paste to remain for several days, then roll out on a board and cut into lengths. A belter method, however, would be to press the crayons in a mould: they would be harder, more homogeneous, and less liable to break.