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toning, image, gold and water

PLATINUM TONING.--As is generally known the chief substance used in photography for toning the photographic image to an agreeable color is gold. The chemical similarity between gold and platinum led to experiments being made with the latter metal to replace the former. The first published formula for a platinum toning process was given in " La Lumiere " (Feb.; 1856)* by a Frenchman, M. de Carranza. He employed an acidulated solution, z in 2,00o of platinic chloride. This was followed by a number of other formulae, among which must be mentioned those of Mr. Burnett.

M. P. Mercier givest the following two rules relating to toning with platinum: First, the bath must be acid, and second it should contain a minimum quantity of a salt, for if the silver which constitutes the image is submitted to the action of an excess of salt it is transformed into chloride without any metallic deposit being formed to replace it. The reaction is repre sented thus: Ag+ PtCl 2 =AgC1+ PtCl.

Consequently the detail of the image rapidly disappears.

If on the other hand the silver is in the presence of the minimum quantity of salt, it is replaced by a deposit of platinum and the image remains unaltered while changing color.

Ag + K PtC1, =KC1 + AgCl.

M. Marset publishes a formula for platinum toning and fixing combined. It is as follows:

A Distilled water ioo c.c.

Platinic chloride 1.5 grammes B Distilled water goo c. c.

Sodium acetate tryst 3o grammes Sodium h yposulphite 15o grammes The prints are first washed, then immersed in the following mixture until the desired tone is obtained, Solution A zo parts Solution B go parts The most modern method of toning with platinum has, however, been devised by Lyonel Clark, C. E., who in the year 1890 published a book upon the subject.II His method is described in this as follows: The print upon the albuminized or upon plain salted paper is made in the usual way, that is to say, just slightly over-printed, as for gold toning. A negative that will give a good gold print will give a good platinum one. Matt surface paper requires stronger negatives than albu men paper. The general rule is that the pluckier the negative the richer the blacks or browns obtained. A weak negative will never give a good result.

The prints when removed from the frames may be stored away until required. They are first washed in two or three changes of water until all milkiness has disappeared.

The toning bath for black or brown tones is prepared as follows: