Ox Gall, the bile of the ox, a viscid green or greenish yellow fluid, of bitter and slightly sweetish taste, found chiefly in a membranous bag in the ox. It varies in consistency, sometimes being very limpid, and at others like a sirup. (See Bile.) It possesses properties which render it of value in the arts. It dissolves greasy matters, and for cleansing woollen stuffs upon a large scale it is sometimes preferred to soap. To preserve it from putrefying it need only be evaporated at a gentle heat to the consistency of an extract; and when wanted for use it may be dissolved in water slightly alkaline. The purified ox gall is much used by artists on account of its property of combining with colors, giving them more tenacity and fixing them strongly, while it also makes them flow more freely and often increases their lustre. It may either be mixed with the colors or applied to the paper after the colors. It is advantageously applied combined with gum Arabic as a light varnish, which however admits of other shades being added without mixing with the first. With lampblack and gum water it makes a beautiful black paint or ink that may be used instead of India ink. The lampblack is first mixed with the gum water, and the purified ox gall is then added.

It fixes sketches in lead pencil, and does not prevent them from being afterward tinted with colors in which a small proportion of ox gall is mixed. It is highly recommended for use in painting on ivory, as it removes from this all greasy matter, and causes the colors to spread freely, and penetrate into the ivory. It is equally useful in the application of paints to transparent paper. For these effects it is essential that the purified article should be prepared from very fresh ox gall. The method of purifying in best repute is as follows: To a pint of the gall boiled and skimmed add an ounce of pulverized alum, and leave the liquor on the fire till the combination is complete. Another pint is treated in the same way with an ounce of common salt instead of alum. When cold the liquids are separately bottled and loosely corked. They should then be kept for three months, when a sediment subsides, and the liquor becomes clearer. There is still present a yellow coloring matter which would affect green and some other colors, and which is separated as a coagulum by turning off and mixing the clear portions of the two mixtures in equal quantities. The liquid is then obtained by filtering perfectly purified and colorless.

It improves by age, and never disengages a bad odor, nor loses its useful properties.