Leather is sometimes dyed in the vat and sometimes by simply brushing over with the dye liquid. For instance, a leather may first be tanned and then transferred to a vat containing pine and elder barks to give it a tan or russet brown colour. Browns and yellows are obtained by damping the leather and brushing over it a decoction of saffron, annatto, a mixture of brazil wood and yellow berries, etc., also by using a solution of an aniline dye, as picric acid, phosphine, Bismarck brown, or acid brown. Other suitable dyes are magenta, methyl violet, Russian green, brilliant green, methylene blue, crysoidine, nigrosine, etc Blacks are usually obtained by brushing over with a decoction of galls and, after drying, a solution of copperas or pyrolignite of iron. After dyeing the leather and drying, it should be rubbed up with a waxed cloth to impart a dull polish. Many of the aniline dyes are best fixed by an after treatment with a decoction of nutgalls. Picric acid may also be used for fixing purposes, but it yields compound shades.