BELITZKI'S REDUCER FOR GELATINE PLATES.
Water 7 ounces Potassium ferric oxalate 24 drachms Crystallized neutral sodium sulphite 2 drachms Powdered oxalic acid 3o to 45 grains Sodium hyposulphite 14 ounce The solution should be made up with the ingredients added in the same order as written. It is then filtered and kept in well-corked bottles in subdued light, the influence of light being to reduce the ferric salt to ferrous. Ottomar Jarecki has suggested a modification of this reducer. His formula is as follows: Water 7 fluid ounces Sol. chloride of iron 2 fluid drachms Potassium oxalate 3 drachms Sodium sulphite, cryst 2 drachms Oxalic acid, about 35 grains Sodium hyposulphite 1 f ounces, ay.
The solids are powdered and the chemicals are added in the above order, dissolving one before adding the next. The color reactions that take place are an amber color when the iron solution is mixed with the water, an emerald green on adding the neutral oxalate of potassium; a ruby red with the sulphite of soda, and the original green restored on dissolving the oxalic acid; in fact, the oxalic acid is added little by little until this green color appears, and at the same time the smell of sulphurous acid is perceptible. The color remains the same after addition of the hypo. It is desirable to filter finally.
Equal parts of each solution are mixed before using, and a small quantity a the mixture added to a strong solution of hypo. The plate is then immersed, or the solution applied locally,
and the image rapidly weakens. The chemical action of the reducer is to convert the silver of the image into oxalate of silver, which is immediately dissolved by the sodium hyposulphite.
Local reduction is a term applied to the reduction of certain portions of the negative only. This is done when the film is quite dry by rubbing it with a soft pad moistened with alcohol until the density is reduced as required. The pad is usually composed of a tuft of cotton-wool or a piece of wash-leather, flannel, etc. For sharply-defined outlines, a pointed stick of soft wood is used steeped in alcohol.
The above remarks all apply to the reduction of gelatino-bromide dry plates. Prints upon bro mide paper may also be treated in the same manner.
Prints upon albumenized paper which have been over-printed can be reduced by immersion in a solution of cupric chloride, or before toning, by using platinic chloride in place of the gold salt.
Prints on collodion paper can be reduced by immersion in a very strong solution of hyposulphite of soda before placing in the combined toning and fixing baths.
Cyanotype or ferro-prussiate prints can be reduced by immersion in a weak solution of am monia, and afterwards into a weak solution of hydro chloric acid.