The following process will produce black lines on a white ground from an ordinary drawing. Soak 150 gr. of gelatine in 5 oz. of water, then place the containing vessel in a saucepan of hot water until the gelatine is dissolved. Mix together 100gr. each of ferrous sulphate, ferric chloride, and tartaric acid in 5oz. of water. Add this to the warm solution of gelatine, and coat the paper quickly whilst the mixture is still hot by rubbing it over the surface. Choose any close-grained paper that is not too absorbent, pin this down flat, and apply the sensitising solution as evenly as possible with a sponge or a Buckle or Blanchard brush. The paper, when dry, is exposed to sunlight for ten minutes to half an hour, according to the density of the drawing on top of it, the two being kept in close contact in a frame or by laying both on a cloth-covered board with a heavy sheet of glass above. A faint yellowish image is printed, which is developed with oxalic acid 20gr., gallic acid 100gr., water 30 oz. It is an advantage to have a test negative at the side, with strips of the paper, which may be withdrawn as printing proceeds and developed as a guide to exposure. Undei--exposure is shown by a sort of fog or veil over what should be the clear portions.

When development is complete, pass the print through a bath of water rendered acid with oxalic acid or sulphuric acid; then thoroughly wash in running water. When placing to dry, press the print between blotting-paper. This process, sometimes known as the ink process, was introduced by Porterin about 1860.