Sensitive papers ought not to be exposed in the frame until they are quite dry. The shutter at the back of the frame is removed, and the negative laid flat upon the glass, collodion-side uppermost. A sheet of sensitive paper is then placed upon the negative, sensitive-side downwards, next comes a layer of thick felt; and the whole is then tightly compressed by replacing and bolting down the shutter. The amount of pressure required is not very considerable, but if the springs of the frame become too weak after a time, a few pieces of mill-board may be placed beneath them.
The time of exposure to light varies much with the density of the negative and the power of the actinic rays, as influenced by the season of the year and weather.
If the exposure to light has been correct the print appears slightly darker than it is intended to remain. The toning bath dissolves away the lighter shades, and reduces the intensity, for which allowance is made in the exposure to light. A little experience soon teaches the proper point but much will depend upon the state of the toning bath, and albuminized paper will require to be printed somewhat more deeply than plain paper. If, on removal from the printing-frame, a peculiar spotted appearance is seen, produced by unequal darkening of the chloride of silver, either the nitrate bath is too weak, the sheet removed from its surface too speedily, or the paper is of inferior quality.
If, in the exposure to ordinary diffused daylight, the shadows of the proof became very decidedly coppery before the lights are sufficiently printed, the negative is in fault. Ammonio-nitrate paper highly salted is particularly liable to this excess of reduction, and especially so if the light is powerful.
The print should be first washed in common water until the soluble nitrate of silver is removed. This is known to be the case when the liquid flows away clear; the first milkiness being caused by the soluble carbonates and chlorides in the water precipitating the nitrate of silver. Ten minutes in water running slowly from a tap will be sufficient to cleanse a print from nitrate of silver; or three or four changes in a dish, pouring off quite dry between each change. It is an advantage to finish off with a solution of salt (2 grs. to the oz.) Pour the toning bath out into a flat dish, and put the prints into it 2 or 3 at a time, waving the dish meanwhile backwards and forwards to secure a constant movement. Continue to keep the prints moving, and watch the changes in color.
If the prints are removed as soon as the blue color of the gold is seen, they will usually change in the fixing bath to a warm shade of brown, but when left for 2 or 3 minutes longer in the toning bath, the darker tint becomes permanent.
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