Amongst the various printing processes in common use amongst photographers, platinotype is unique in several respects.
Printing is conducted by daylight in precisely the same manner as silver printing, but the action of light only suffices to make the image partially visible. In this respect, platinotype stands, as it were, midway between what are familiarly termed "print-out" processes—that is, those in which the image is made completely visible by daylight, and those in which the action of light is latent or invisible, such as bromide paper and in the carbon process.
The distinctive character of the platinotype print, with which, probably, everyone is so familiar that a platinotype effect almost amounts to a generic term, is not so much essential to the process, but has been largely determined by the different kind of papers and the preparation of those adopted by the manufacturers of platinotype printing papers.
In the first place, the platinotype print is before anything a matt surface print, and possesses a certain kind of texture or surface which gives the finished print an appearance similar to a pencil drawing or an engraving; an appearance largely assisted by the characteristic colour of the platinum image, which is black.
The invention and production of platinotype paper is due to Mr. Willis and the Platinotype Company, and although subsequently there have been both English and foreign imitators, we may safely confine our attention to those papers made and supplied by the Platinotype Company.
As, however, the purpose of this article is to furnish the beginner with simple working instructions, rather than to describe the principles of the process, we will at once proceed to say how a platinotype print is made.
To begin with, platinotype printing is divided into cold-bath process and hot-bath process. Of the latter we shall speak later on, but for the present, as being most suitable for the amateur and beginner, we will consider the cold-bath method. The reason for this division and the meaning of the name will be abundantly evident presently.
We first of all procure a tin of paper of the quality marked AA. The paper is put up in tin cylinders containing twenty-four pieces of either ¼-plate or ½-plate sizes, or less for larger sizes. It may, if preferred, be obtained in full-size sheets 20 × 26 inches.
We have now to bear in mind that the paper is sensitive to daylight to a slightly greater degree than are the silver print-out papers, and hence, whilst handling the paper, placing it in the printing frames, or what not, we need to be a little more careful as to how near the window we bring the paper. At the side of the room furthest from the window, or with an intervening screen between the paper and the window, or yet again, with the blind drawn down, we shall be quite safe in opening our tin of paper and inspecting it.