To make the black enamel for ferrotype plates, mix together amber 90 parts, black resin 69parts, spirit of turpentine 45 parts, and painter's varnish 45 parts, and add sufficient lampblack to give the desired blackness. The varnish is contained in an upright hath and the plates in fairly large sizes dipped and afterwards cut up. Then coat with collodion and sensitise as usual.