D. MERCURIC SOLUTION. Mercuric chloride 20 parts solution at 5:100 Sodium oxalate solution 40 parts at 3:100 Glycerine 2 parts
SENSITIZING SOLUTIONS. FOR BLACK TONES. Platinite solution, 1:6 5 parts Solution B 6 parts Solution C 2 parts
FOR SEPIA TONES. Platinite solution, 1:6 5 parts Solution C 4 parts Solution D 4 parts
Intermediate tones are obtained by diminishing the dose of C and replacing it by an equal volume of B. For this process the paper should be sized with
Arrowroot 2 parts Sodium oxalate at 3:100 100 parts
To dispense with this preliminary sizing Captain Pizzighelli adds gum arabic to the platinite solution, whereby the sizing and sensitizing are done in one operation.
The gum arabic solutions are prepared as follows:
E. Gum arabic in 40 parts powder Sodium ferric 40 parts oxalate solution, B Sodium oxalate 100 parts solution at 3:100 Glycerine 3 parts
Place the glycerine and the gum arabic in a mortar, then, stirring with the pestle, dissolve by adding, little by little, the mixture, heated to 40—45 deg. C. (104—113 deg. Fahr.), of the solution of sodium ferric oxalate and sodium oxalate. Let stand for about two hours and grind again to dissolve entirely the gum arabic. Filter through muslin.
F. Mercuric chloride 20 parts solution, 5:100 Sodium oxalate solution, 40 parts 3:100 Gum arabic in powder 24 parts Glycerine 2 parts
SENSITIZING SOLUTIONS. FOR BLACK TONES. Platinite solution, 1:6 5 parts Solution E 6 parts Solution C 2 parts
FOR SEPIA TONES. Platinite solution, 1:6 5 parts Solution C 4 parts Solution F 4 parts
Mix just before use. The solutions do not keep. The paper prepared by either one of these two processes can be exposed as in the _old_ process, and the image developed bythe hot oxalate solution.
The preparation of wood, canvas, etc., for the platinotype printing need not to be described; it suggests itself.
This defect may result from various causes, viz.:
1st. The stock ferric oxalate solution is impaired by a partial reduction of the ferric salt into ferrous oxalate. The solution should be preserved in an orange colored vial, and kept in the closet of the dark room. It should be tested from time to time for the ferrous salt with a solution of potassium ferricyanate. If it does not contain any ferrous oxalate it can be used by adding to it a little of the iron chlorate solution. 2d. The paper has been exposed to light during the sensitizing or the subsequent operations. One should bear in mind that the platinum paper is twice more sensitive than silvered paper. 3d. The sensitized paper has been dried at a temperature above 40 deg. C. (104. deg. Fahr.) 4th. Over-exposure.