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In less than a minute the syrupy fluid has dried, and appears like a film of transparent varnish on the glass plate. We now place it on a flat double hook of gutta percha and lower it gently into the nitrate-of-silver bath. As it must remain there three or four minutes, we will pass away the time in explaining what has been already done. The syrupy fluid was iodized collodion.
The use of the collodion is to furnish a delicate, homogeneous, adhesive, colorless layer in which the iodide may be deposited. Its organic nature may favor the action of light upon the iodide of silver. While we have been talking and waiting, the process just described has been going on, and we are now ready to take the glass plate out of the nitrate-of-silver bath.
The second is in timing the immersion in the nitrate-of-silver bath. This is easily overcome; the glass may be examined by the feeble lamp-light at the end of two or three minutes, and if the surface looks streaky, replunged in the bath for a minute or two more, or until the surface looks smooth.
It will be observed that the glass plate, covered with its film of collodion, was removed directly from the nitrate-of-silver bath to the camera, so as to be exposed to its image while still wet. It is obvious that this process is one that can hardly be performed conveniently at a distance from the artist's place of work.
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