Читать книгу Photography in the Studio and in the Field - Edward M. Estabrooke - Страница 7

While the glass is still wet from the washing, after being taken from the acid, it should be coated with a preparation of albumen, prepared as follows: p12

To the albumen or white of a fresh egg, add eight ounces of water; put it in a bowl and thoroughly beat it with an egg beater, or in any manner that may be convenient, until the fibre or structure is completely destroyed, when it should be filtered through loose cotton, and after the addition of a few drops of strong ammonia, it is ready for use.

Many prefer to beat up the albumen before adding the water, in which case it should be beaten into a stiff froth, when the proper amount of water is added, and after the froth has subsided the whole is filtered and the ammonia put in last.

The albumen being prepared and the glass ready, a square is taken in the left hand, and clean water flowed over it, until no particle of dust can be seen adhering to either surface, when a small portion of the albumen is flowed on it, and after covering every part of the surface the excess is allowed to drain off the right hand lower corner, after which, if running water is at hand, the back of the same portion of the plate should be passed under the faucet, and the water will carry off any excess of albumen which might return or crawl, as it is termed, up the back of the plate from the point where it is drained.

The greatest care should be taken to avoid dust settling on the plate during the coating and afterwards while drying, and after the glass has been coated, if it is found that any dust adheres to the albumenized surface, it should be again washed and recoated.

It is important that the back of the glass should be kept free from the albumen, so that when the plate is afterward collodionized and immersed in the silver solution, there should be no albumen uncovered to p13 contaminate the bath, and as most of the glass used has some slight inequalities of surface, the albumen should always be flowed on the concave side, for two reasons:

The first is, that when sensitized and placed in the holder, the pressure, being against the convex side, may have a tendency to counteract the curve and make the plate flatter and more perfectly adjusted to the focus.

The other reason is that the pressure of the printing frame has a less tendency to break the glass when against the concave side.

The amount of glass required having been albumenized and set up in racks, it should be carefully covered with paper to exclude dust, and it should be set away to dry, after which it should be placed in its proper receptacle in the dark room, ready for use.

The reasons for albumenizing the glass are important.

Before this process was adopted, all glass used for photographic purposes, after being subjected to the action of potash or acid, or both, had to be finely polished with rottenstone or some other polishing substance, to render its surface sufficiently free from all traces of acid, organic matter, rust, etc., which would injuriously affect the collodion or the deposit of silver iodide derived from the bath.

This polishing was very laborious, and in consequence it was often very imperfectly done, causing much loss of time and material; also the glass thus prepared did not offer to the collodion a surface to which it could adhere with much tenacity, and in consequence it would frequently slip from it in the subsequent manipulations. p14

The first reason for Albumenizing then, is to cover the surface with a substance chemically pure, and when dry of a crystaline nature and impervious to, or at least not soluble in the silver solution, thus saving the labor of polishing.

Another reason is that the albumen offers a surface to which the collodion will adhere with extreme tenacity, thus saving and preventing the film from slipping.