Thus much for negative making.
Films fix quicker than glass dry plates, and the completion of the operation can he ascertained by tin - even, translucent appearance from the back while lying in the bath, or by examination by transmitted light. After fixing, wash in several changes of cold water, the longer the better, and the film is then ready for transferring to its final support.
Coat a clean glass plate, polished with French chalk and, say, one size larger than the film, with plain collodion; well wash until all greasiness is removed. Lay the film negative face downward in a tray of cold water, and slip the glass plate, collodion side up, under it. Grasp the film by one edge of the glass and lift from the tray, allowing the water to drain from the side furthest from you. All surplus water can now be removed by the scraping action of a rubber squeegee, and the plate supporting the film set to soak in a dish of warm water, increasing the temperature until the paper commences to blister. Lift one corner of the paper with the point of a pin, and gently pull it off from the film, which will adhere to the collodion on the glass. Remove from the film with warm water all traces of the soluble substratum which was between the paper and the film.
The image - bearing film is now on the glass, with the paper removed. If intensification should be necessary, the operation can be performed in the same manner as with glass dry plates.
Allow the film to remain in the above bath until it is thoroughly whitened, the bleaching being complete; the mercuric solution is rinsed off, and the negative is immersed in a mixture of equal parts of a saturated solution of sodium sulphite and water; the darkening action will be seen to take place steadily and slowly, just as when ammonia is used. The negative must be well washed, and is now ready for strengthening the film by adding a sheet of gelatine "skin." I prepare these skins any length of time beforehand, and keep them between the leaves of a book; they are thus always ready for use. I am indebted to Mr. Ernest Edwards, of the Photogravure Company of New York, for the manner of preparing these skins.
Take as many sheets of thick glass, with ground surface, as you wish to make skins; polish well with French chalk, and flow with the following solution:
Gelatins (Nelson's, No. 3) ...................
Set on a level place to dry. They may be made in large sheets and cut up for use. Take a piece of skin prepared as above, the same size as your negative film, and put it into a tray of clean, cold water, and as soon as limp lay it upon the negative film (already held