A modification of the above process has been introduced, in which, paper-coated with an iron salt, ferric oxalate, is exposed under a negative, till the image is distinctly visible, and it is then developed upon a mixed solution of oxalate and chloro-platinite of potash. In the hot process the platinum and iron salt are applied to the paper, but in this the platinum is deposited on the paper from the developer.
It is claimed for this paper by Mr. Willis, of the Platino-type Company, the inventor, that several advantages accrue from the use of this process, viz., greater transparency in the shadows, tentative and cold development, shorter exposure, and easy variation in the tone of the resulting print. For full details the beginner is referred to the instructions issued by the above company. The question as to which is the best process depends solely upon the amount of work to be done, few prints and occasional are best treated by the hot process, as in this case the cold process is rather more expensive, but where much work is required the cold process should be adopted.
A process invented by Captain Pizzighelli is one well worth attention by any amateur. Paper-coated with a mixture of Ferric, and Alkaline Oxalate, and a salt of Platinum, with some organic matter, such as gum or starch, is exposed under a negative in the ordinary way, and when the image shows distinctly, the paper is either steamed by means of a kettle, or breathed upon when the image starts up into a permanent and pleasing black, formed by the reduction of the Platinum salt. Full directions will be found in the instructions as issued by the makers.
One of the earliest and certainly in results the most pleasing of all processes for the production of prints, which can be produced in almost any colour and upon any material, the only objection being, that negatives which are reversed as regards left and right must be used unless what is called double transfer is used, or one of the film negatives. The full directions are so complete and numerous, that the amateur is referred to the Manual of Carbon Printing by the Autotype Company. The paper, or tissue, as it is called, is coated with a gelatine containing colouring matters, and is sensitized with bichromate of potash, exposed to light, the duration of exposure being timed by an actinometer. The paper is then temporarily affixed to a Support and developed from the back with water at 110° Fahr., and the print soon shows in all its beauty, and is then fixed in cold water and alum, or is transferred to its final support. The paper is cheap and can be bought ready prepared, in which state it will keep for about a fortnight, and from the facility with which coloured prints are obtained, the process should find a place in every amateur's work.