The wood printing frame itself, if it has been used for printing in the open air, should be placed in an oven or held near the fire to thoroughly dry it.
Having placed the negative and the platinotype paper in the frame in the ordinary manner, there should next be placed at the back of the paper a thin sheet of waterproof cloth, vulcanized rubber of the proper size and thickness being sold for the purpose; this will prevent damp from penetrating to the paper from the back of the frame. The frame may now be closed and placed in the light for printing, and even having taken all these elaborate precautions against damp it would not be advisable to print out of doors except in dry weather, nor should the paper be left in the frame longer than need be, but if it is not proposed to finish the print off at once, it should be returned as soon as convenient to the security of the calcium tube.
GENERAL OUTLINE OF THE PROCESS.
Platinotype paper is ordinarily only available for daylight printing, though the Platinotype Company have introduced a lamp of special construction and great power, by the use of which daylight may be dispensed with, and electric light, should it be available, may be used.
As has been already said, platinotype paper is rather more sensitive to light than silver paper, and hence takes proportionately less time to print.
The duration of the exposure to light constitutes the only real difficulty in platinotype printing, and whilst just at first it may result in the beginner's meeting with much disappointment, yet probably, with a little care and watchfulness the trouble will be surmounted, and sufficient experience gained to secure fairly uniform success thereafter, before even the first tube of paper has been used.
The printed image shows on the yellow ground of the sensitized side as a faint grey, the darkest portions assuming an orange-grey tint, whilst the lighter parts remain all but invisible.
A little practice will enable one to judge the right depth, that is to say, how visible the image should be before printing is to be stopped, but as a rough guide to commence with it may be said that printing is complete when the image is about half as deep as we should expect it to be if it were a "print-out" process.
As we shall have occasion to return to the question of printing presently, we may now pass to the next step in the process.