To obtain a white ground on drawing boards so that drawings made with charcoal and coloured chalks may be easily rubbed out, mix dry white lead to a stiff paste with gum arabic dissolved iu water-, add water till it works easily, like paint. When applying it, either stipple it with a hog-hair brush or cross and re cross it till no brush marks are seen. A little of the white should first be tried on the corner of the board. Let it dry, then rub the fingers over it. If it rubs off on the fingers, add move gum; if it shines, there is too much gum. To dissolve the gum, saturate it with water and stand in a warm place.