To make a bas-relief in plaster-of-Paris from a photographic negative, the process briefly is as follows: - Soak a sheet of No. 4 gelatine in a solution of bichromate ot potash, made by dissolving 1 dr. of bichromate in 6 oz. of water; allow this to dry slowly (generally taking twenty-four hours) in contact with waxed or French-chalked glass. The glazed surface thus obtained is placed in contact with a suitable negative, that is, one containing considerable contrast combined with good gradation, and exposed to the light. In half an hour, or in five or six hours, according to the strength of the light, a faint image will have been printed on the gelatine. When printed, the gelatine is firmly cemented to a sheet of glass with isinglass or other powerful adhesive, and allowed to soak in cold water for about six hours, afterwards soaking for a further time in a 1 in 4 solution of citric acid, and finally in water. When the utmost possible amount of relief has been obtained, the superfluous moisture is carefully removed with the edge of a blotting board, and oil is poured over the gelatine mould, and then drained off. The gelatine relief is then placed in a dish, and the plaster poured over it and allowed to set, after which the relief may be pulled off.

The relief thus obtained is generally rather false owing to differences in colour - particularly if isochro-matic plates are not used - being grossly exaggerated. Much may be done by skilful retouching.