Is prepared either by long boiling the shreds of parchment &c., or from glue by soaking in cold water, and subsequently dissolving by heat. The quantity to be used depends like that of gums on the quality of the pigments employed, and caution is more necessary than with the gums not to use it in excess on account of its disposition to contract in drying, and occasion the colour to crack and scale off. The lighter coloured fish-glue and isinglass are substituted for the nicer kinds of painting; albumen or white of egg, and also the yolk employed by glovers, is used in some cases; oxgall useful when the surface to be painted is polished, or works greasy. Size is sometimes worked into oil colours instead of mastic varnish to gelatinize and give them crispness.