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.

COLLODION.

"The discovery that explosive cotton was soluble in ether, was made by Mr. Maynard, who gave it the name of Collodion, and later, in 1848, published in the American Journal of Medical Science the formula for its preparation."

"This ethereal solution, having a certain proportion of alkaline iodides, and iodides of silver added thereto, constituted the collodion first employed by Mr. Archer," who thus shares with Mr. Maynard, and with a Mr. Legray (who first published an account of its use as a photographic agent) the honor of having given to the world the collodion process in photography.

The progress that has been made since Mr. Archer's time in perfecting the adaptability of collodion to photographic uses could not be better illustrated than by comparing the formulæ for collodion first published with those in use at this time.

The practice of photography in the present day by the collodion process is divided into two branches, the positive and the negative.

In the first the object is to obtain in the camera a p15 direct image, which is to be viewed by reflected light, and as it is desired that the pictures so produced should possess pure blacks and whites, certain modifications of the collodion, silver solution and developer are resorted to, which cause these preparations to differ somewhat from those prepared for the production of superior negatives, consequently the formulæ given hereafter will be designated as positive or negative.

These modifications, however, are not of such a character as to render either of the solutions prepared for one process totally unfit to be used for the other, for in fact, many photographers at this day use the same collodion bath and developer for making both positives and negatives.

THE POSITIVE COLLODION PROCESS.

In the first place, we will take up for consideration the positive process.

The first positives on glass were called ambrotypes, and were the successors to the daguerreotype, which they superseded and displaced by the superior facility of their production.

For the same reason the ambrotype was succeeded by the ferrotype, which was a positive collodion picture, made on a thin iron plate with a black japanned surface.

The ferrotype or tintype is now about the only product of the positive collodion process of considerable importance, and is the only one that will receive consideration in these pages.

Ferrotype plates are sold by all dealers in photographic materials; they are mostly manufactured by two large concerns in Worcester, Mass. p16

COLLODION FOR POSITIVES.

As has before been stated, to produce the finest results in positive photography requires certain modifications of the collodion bath and developer, which, while not unfitting them altogether for negative work, yet would render them quite unsuitable for high class work.

The formula for positive collodion here given has many merits, and among those is a certain quality of film, which might be termed opacity, but not in the strict sense of the word; it is that quality in the film which enables it to cover up any small scratch or water mark on the surface of the plate that would infallibly spoil the picture, if almost any other collodion were used.

This quality, with great clearness or transparency in the shadows, and a beautiful gradation of light and shade, make it unique as a positive collodion.

There may seem to be a contradiction between the terms opacity and great transparency of shadows, which may need further explanation. As the shadows of a positive collodion picture are produced by the black surface of the plate showing through the collodion, any defect on that portion of the surface would be expected to show very plainly, and it does so with the use of the ordinary collodions sold by the dealers, but not so with the collodion under consideration, which may be because it is less permeable by the silver solution, and that consequently the deposit of iodide of silver lies more on the surface and less within the texture of the film, and is thus kept from contact with organic matter or other defects on the surface of the plate; in some such manner only, can I account for a very valuable quality that has saved thousands of p17 plates, that would under other usage have been thrown away.

This formula has never before been published, and must be prepared as directed.

Alcohol and ether equal parts; gun cotton sufficient to make a moderately thick film, say 5 or 6 grains to the oz.; put the cotton in the ether first; when it is well saturated, pour in the alcohol. To which add:

The latter ingredient can only be had in aqueous solution, I believe, and requires close calculation to get at the right quantity.

This formula gives 8 grains of salts to the ounce of collodion, and would require a silver solution of 50 grains to the fluid ounce to balance properly.

The silver solution may be prepared as per directions on page 29, under the heading—The Negative Bath.