Probably all photographers are sufficiently familiar with this process to know that in printing the platinotype paper the image which appears is not brown or purple, but of a faint greyish-yellow colour, and therefore it is rather difficult to judge whether a print has had sufficient exposure in the frame, as may be done in the case of albumenised paper.
To remove this drawback, which to some degree has been prejudicial to the popularity of this printing process, Capt. Pizzighelli, to whom we are indebted for much valuable information on the subject of platinum printing, • has made many experiments, but only recently has he succeeded in finding out a method of producing platinotypes directly in the printing frame without development.
The principles of this method are the following:
2. If to the sensitising solution one of those substances which serve as developers is added in the very beginning, a reduction of the platinum salt takes place directly in the printing frame by atmospheric influences.
The advantages of the new process are, therefore, very important, as there is no longer a necessity for a preliminary preparation of the paper, and as you can judge of the exposure as accurately as with silver. Besides this, the development of the paper is entirely omitted. A simple, short washing of the "prints, first in acidulated, then in ordinary water, is sufficient for finishing the pictures.