Canvasses, &c., that have been kept for a considerable length of time previous to using, are apt to receive from the atmosphere, a greasy deposit, which, though imperceptible to the eye, is of sufficient quantity, greatly to retard, and often altogether to prevent the drying of the colours that are laid on them; to remedy this, before using them, they should be placed in a horizontal position, and carefully rubbed with a piece of flannel and finely powdered pumice-stone, well sifted; they should then be washed with a weak solution of sugar of lead in water, applied with a rag or sponge, which may be allowed to dry on them, the powdered pumice must then be applied again, and removed with a brush: ,,