These different kinds of glue, which differ from each other only by the greater or less degree of their purity and colour, may be applied to different kinds of works, according to their fineness. The first kind is destined to defend delicate painting, coloured paper, painting in water-colours, &c., from the attacks of varnish. That of the second quality may be used, with the precautions already mentioned, for the same purposes. That of the third is employed for common sizing