Plates, Sizes of Platinotype
are wanting. The print is then taken from the frame and put on one side, when the action set up by the light continues, and in from a half to two hours the print is finished, and can be treated as above in acidified water, or the incomplete picture may be developed upon a cold dilute solution of carbonate of soda of the following strength : -
Carbonate of soda ... ... 38 grs. or 2 grms.
Distilled water ...... 27 drms. ,, i5oc.cm.
Immerse the print in this till sufficiently developed. A third method of printing is to expose till only the principal details are visible, and develop, as in the old process, upon a hot solution of potassium oxalate.
Plates, Sizes of. See Sizes, Photographic.
Platino-bromide. A somewhat misleading term occasionally applied to developed silver prints.
Platinotype. The basis on which this process is founded is the reduction of ferric oxalate by the action of light into ferrous oxalate, and the reduction of a platinum salt by the ferrous oxalate, when wetted with a suitable agent. The following are concise directions for the process: - Paper of good strong quality, even in texture and white in colour, should be chosen, and may be sized in one of the following baths: - Soak 150 grs. of Nelson's X opaque gelatine in 30 ozs. of water for half an hour, and heat in a water bath at a temperature of 1400 F. to dissolve it. Add 45 grs. of powdered alum and 7 ozs. methylated spirit, filter through muslin, and put in large flat dish. Thoroughly immerse the paper bodily in this solution, taking care to break all adherent bubbles; the paper should be allowed to soak for three minutes, and then hung up by clips to dry. The drying should be as rapid as possible, and a second bath for the same time should be given, and the paper hung up by the opposite corners. A sizing of gelatine tends to a bluish black tone; arrowroot and starch to a brownish tinge. If arrow-root or starch be used, the following bath may be prepared: - Rub 150 grs. of arrowroot or pure starch powder into a cream with a little water, and then pour gradually and with constant stirring into 30 ozs. of boiling water, and boil for ten minutes;