Soak until the gelatine is soft, then melt by setting the vessel in hot water, and when completely melted, stir in -
Liquid ammonia ..» .». ... ... 4 drops.
Powdered bichromate of potassium ... 10 gr.
Skim off the surface skin and all air-bubbles, using strips of thin card as skimmers, and now flood the plate, which is supported, ground side upwards, on the wine-glass. As soon as the gelatinous mixture is on the plate a more accurate levelling can be obtained by noticing where the liquid tends to flow off, and wedging up the foot of the glass by means of match-stems cut taper. Finally, pour on as much as the plate will hold, or about one-sixteenth of an inch in height. All this must be done quickly, and before the mixture sets; but by previously warming the plate the setting of the mixture will be hindered, and more time becomes available. The plate should now remain at rest until the mixture sets, when the plate can be set up on edge to dry, in a photographically dark room of course. Next expose in a printing-frame under a negative for about one and a-half times as long as would be necessary for printing-out paper, or until all details are visible, in a darkened tint, at the back of the plate. Now soak for five or ten minutes in cold water, when the gelatine will swell and give a most delicately modelled bas-relief. A cast must be made from this in plaster while the gelatine is wet, and the plaster cast is a basis for any further reproduction. To cast in plaster, a small quantity of oil is dabbed on the gelatine relief with a hog-hair brush, and four strips of wood are placed round the plate, so as to leave a recess about an inch deep. Into this recess is poured the plaster of Paris, mixed with water to the consistency of thickish cream, and, with a view of removing any air bubbles, a camel's hair brush is worked through the liquid plaster so as to once sweep the surface of the gelatine relief. When the plaster is quite set, the thin edge of a knife should be inserted under one edge of the cast, and the cast is separated by a slight and very slowly increasing strain applied by forcing the blade to an angle with the face of the plate. When the plaster cast is obtained, a reproduction can be made from it in metal, earthenware, ebonite, or almost any material."