OZOTYPE A pigmented gelatine process, patented by Thomas Manly in 1899, differing from the usual carbon method. Sized paper is coated with a solution containing a bichromate and a man ganous salt. This preparation is sensitive to light, and under a negative produces a positive image in manganese chromate. A pigment plaster (paper coated with pigmented gelatine) is soaked in an acidulated solution of a reducing agent, such as hydroquinone or ferrous sulphate, and applied to the washed image. The action of the acid produces chromic acid which is imme diately reduced by the hydroquinone or ferrous sulphate, with the result that the gelatine is tanned. In practice, the ozotype process is carried out by coating well-sized drawing paper with the ozotype sensitising solution, thoroughly drying, and printing under a negative in day light. The image is of a light brown colour and distinctly visible. When all details appear the image is carefully washed for a limited time, as it is slightly soluble. A piece of pigment
plaster is then soaked for 3o to 6o seconds in the following bath : Glacial acetic acid . so mins. 4 ccs.
Hydroquinone . 12 grs. i g.
Copper sulphate . 12 „ 1 ,, Water . . . 25 oz. ',coo ccs.
As soon as the pigment plaster is quite limp the chromium print is expeditiously brought into contact with it in the bath, and both papers, clinging together, are withdrawn and squeegeed gently together. The adhering papers are left for 3o to 6o minutes for the action to take place, when they will be ready for development, which is carried out by separating the papers in water at about iio° F. (about C.), and dissolving away all soluble gelatine. The advantages are (1) a visible image ; (2) no reversal of the image ; (3) almost unlimited control with the brush.