The fading of silver prints on albumenised paper is an interesting matter, but one about which we know very little. Those who have given the subject any attention have been struck with the singular fact that skill and care on the part of the maker of the prints is no guarantee of their permanency. In fact, numerous cases could be quoted where prints made in the most slovenly manner, with poor materials, and by men so ignorant that they hardly knew the names of the chemicals handled, have actually outlasted the best efforts of skilled and careful photographers.

In most other departments of practical photography we could say that more careful investigation would help us in determining the causes of fading, even if it proved impossible to entirely do away with them; but the subject is an exceedingly difficult one, partly owing to the complex chemical nature of the silver print, and partly from the impossibility of watching the behaviour of batches of prints, or even of individual prints out of a given batch, for years at a time, and of obtaining data as to their manufacture which would be of any practical value.

From the earliest days of silver printing imperfect removal of the hyposulphite after fixing has been cited as a pregnant cause of fading. The dangers from the said source have been much overrated. Assuming that a good commercial sample of the hyposulphite is used, and that no foreign matter like acids be allowed access to the fixing bath, there is really no reason why a print should not last well, even if quite a large quantity of the fixing salt remains in the paper.

Prints made by an experienced maker of albumenised paper, which had merely received a couple of rinses after fixing, and were then immediately dried, when several years old had remained perfect in every respect.

Every one who has tried silver printing is aware that even the successful toning of the print cannot be accomplished if there is free silver nitrate left in it, but that the said salt must be washed away before the print is risked in the gold bath. Neglect of this means red patches and streaks, alternating with ashy blue tints and mealiness over the entire print, and oftentimes precipitation of the gold in the bath, and consequent stoppage of the toning action. But this is not all.

The proper forming of the image on a silver print demands the harmonious chemical action of three distinct compounds of silver: first, silver chloride; second, the organic chlorific compound of albumen and silver nitrate; and third, free silver nitrate in excess. When a print is taken from the frame and washed, the chloride and a certain portion of the darkened organic compound remain unaffected, while the free nitrate, and in all probability a considerable amount of the organic compound are washed away. Now, the point is whether the too complete removal of this organic compound, in the washing before toning, may not injure the stability of the print by robbing it unduly of one of its important component parts before the gold has had an opportunity of depositing upon it, and ensuring its permanent abode in the print. The objection may be raised that the hyposulphite would remove it in the fixing, but if the gold is well deposited upon it it would remain.

This idea may seem far-fetched, but we can find analogies to it in several departments of photographic chemistry. Take, for instance, the manufacture of washed collodio-bromide pellicle. Here the silver bromide is formed in the collodion by adding silver nitrate to collodion containing a soluble bromide. In order to get rid of the lye salts which come from the double decomposition between the bromide and the nitrate, the emulsion, after setting, is washed in water to remove them. But it sometimes happens that the pyroxy-line is of a variety that will not bear the washing without parting with an organic compound between the silver and the pyroxyline, which seems to form during the ripening of the emulsion. When such is the case, the resulting pellicle gives thin, foggy negatives, and is in every way unsatisfactory.

It was long ago discovered that silver nitrate reacts with such substances as albumen and gelatine (less so with pyroxyline), entering into combination with them; and the albumen compound is the important colorific substance of the silver print. Another fact is, that prints from which all traces of silver are thoroughly eliminated, as, for instance, by prolonged boiling in some chlorinous solution, refuse to tone.

We are therefore driven to the conclusion that prints must contain an appreciable quantity of silver in order to take the gold properly during the toning; but, on the other hand, we know that an excess of the silver is incompatible with good toning. It may, then, be fairly asked how long the prints ought to be washed, before the toning, and the answer to this question can be found only in practical experience. A batch of, say, 150 8 in. X 5 in. prints put into one of the largest porcelain pans obtainable at the stock dealers, and set under an ordinary dark-room tap, would contain a large amount of free silver after 1/2 hour's washing, while a dozen prints of the same size would probably be ready to tone after 10 minutes' immersion or less.

But another objection may be raised. The question will be asked why some prints from every batch fade in a comparatively short time, while the rest remain white for years and years. Now remember that, excellent as our commercial brands of albumenised paper are, it is, nevertheless, an impossibility to coat sheets with albumen so evenly that it shall be of just the same thickness or body at every part of the sheet. The behaviour of the prints, both during the ' printing and after they are finally dried, proves this. Every practical printer knows the value of the thick ends of the sheet, and, if he' is a careful workman, reserves them for the most difficult subjects. Prints made on these "thick ends" will curl in a refractory manner when dried, owing to the heavy body of albumen on the paper, while those made on the more central portions of the sheet remain flat.

Remembering this, is it not fair to assume that prints, even when made from the same sheet of paper, will not part with the organic silver compound equally when washed before toning, owing to the variable thickness of the albumen, and will thus present to the gold a variable quantity of the important organic constituent?

The fact that prints toned in the lime chloride toning bath, without any washing whatever to remove the silver after coming from the frame, last fully as well as others made in the usual way (better, indeed, in some cases), is another item in support of the view advanced.

An enumeration of all the possible causes of the fading of silver prints would be indeed lengthy; but attention may be drawn to the want of reliability of a mountant, which, until very recently, was always considered quite safe. This is gelatine, either when dissolved in water alone or in water with alcohol added to prevent cockling of the mount-not only as a mountant in the usual sense, but also as a material for cementing prints to glass, or as a sizing. On the other hand, prints over 20 years old, which had been mounted with starch, have lasted well, while almost every gelatine-mounted print has faded more or less, according to its age.

The important matters to care for in printing, as regards permanency, are: - A good albumenised paper, free from smell, worked in as strong a silver bath as the salting of the paper will allow, toned rather rapidly after the minimum of washing, and, if necessary, adding common salt liberally to the toning bath to make up for it; to wash off the gold thoroughly before fixing, and to have the fixing bath strong and lukewarm to the finger; to work the prints about thoroughly during the fixing land the first rinses after fixing; to wash them in rapid changes of water; to avoid gelatine as a mountant, and, finally, to rub in wax after rolling, the best means being to reduce pure white wax to the consistency of soft butter with turpentine and a little oil of lavender. This is better than the ordinary burnisher. - (E. Wallace.)