The process of making gelatino-bromide of silver prints or enlargements on paper or opal has been before the public for some years now, and cannot be called new; but still it is neither so well known nor understood as it deserves to be. There is no other enlarging process capable of giving better results, while the ease and rapidity with which enlarged pictures can be made by it are great. To make an enlargement on a 12 by 10 opal, using a sciopticon burning paraffin, an exposure for 2 1/2 minutes is sufficient. Most effective enlargements can be made by the paper process also; indeed, as a basis for colouring, nothing could well be better. Artists say, after a few trials, they prefer it to anything else, while excellent and effective plain enlargements are easily made by it if only carefully handled. A very good enlargement is made by vignetting the picture with the opal, then squeezing it down on a clean glass, and afterward framing it with another glass in front, when it will have the appearance almost equal to an opal. To make sure of the picture adhering to the glass, however, and at the same time to give greater brilliancy, it is better to flow the glass with a 10 or 15 gr. solution of clear gelatine before squeezing it down.
The one fault or shortcoming of the plain argentic paper is the dulness of the surface when dry, and this certainly makes it unsuitable for small work, such as the rapid production of cartes or proofs from negatives wanted in a hurry; the tone of an argentic print is also spoken of sometimes as being objectionable; but probably it is not so much the tone as the want of brilliancy that is the fault there, and if once the public were accustomed to the tones of argentine paper, they might possibly like them twice as well as the purples and browns with which they are familiar, provided they had the depth and gloss of a silver print. Some time ago, acting on a suggestion made by the editor of the Photographic News, Goodall set about trying to produce this result by enamelling the paper with a barium emulsion, previous to eoating it with the gelatinous silver bromide. His experiments were successful, and he now prepares an enamel argentic paper on which the prints stand out with brilliancy equal to those on albumenised paper.
Mention has already been made of the great ease and facility with which an argentic enlargement may be made, as compared with a collodion transfer, for instance; but there is another and more important point to be considered between the two, and that is, their durability and permanence. Now with regard to a collodion transfer, unless most particular care be taken in the washing of it (and those who have made them will well know what a delicate, not to say difficult, job it is to get them thoroughly freed from the hypo, and at the same time preserve the film intact), there is no permanence in a collodion transfer, and that practically, in 9 cases out of 10, they hare the elements of decay in them from the first day of their existence. At least in Glasgow, where an enormous business has been done within the last few years by certain firms in the club picture trade (the club picture being a collodion transfer tinted in oil or varnish colours), there are literally thousands of pictures for which 30s. or more has been paid, and of which the bare frame is all that remains.
A collodion transfer cannot be made even comparatively permanent, unless an amount of care be taken in the making of it which is neither compatible nor consistent with the popular price and extensive output.
Argentic enlargements, setting aside every other quality, are the most permanent pictures that have ever been produced. Chromotypes and other carbon pictures have been called permanent, but their permanence depends upon the nature of the pigment employed, and associated with the chromated gelatine in which they are produced, most of the pigments used, and all the prettiest ones, being unable to withstand the bleaching action of the light for more than a few weeks. Carbon pictures are therefore only permanent according to the degree in which the colouring matter employed is capable of resisting the decolorising action of light. But there is no pigment in an argentic print, nothing but the silver reduced by the developer after the action of light; and that has been shown to be of a very stable and not easily decomposed nature; while if the pictures are passed through a solution of alum after washing and fixing, the gelatine also is so acted upon as to be rendered in a great degree impervious to the action of damp, and the pictures are then somewhat similar to carbon pictures without carbon.
Defects and failures are sometimes met with in working this process. There are frequent complaints of want of purity in the whites, especially in vignetted enlargements; this almost always arises from one or other of the 2 following causes : -
(1) An excess of the ferrous salt in the ferrous oxalate developer; and when this is the case, the yellow compound salt is more in suspension than solution, and in the course of development it is deposited upon, and at the same time formed in, the gelatinous film. The proportions of saturated solution of oxalate to saturated solution of iron, to form the iron oxalate developer, that has been recommended by the highest and almost only scientific authority on the subject - Dr. Eder - are 4-6 parts of potassic oxalate to 1 of ferrous sulphate. Now while these proportions may be the best for the development of a negative, they are not the best for gelatine bromide positive enlargements; indeed, potassic oxalate should not have more than 1/8 of the ferrous sulphate solution added to it, otherwise it will not hold in proper solution for any length of time the compound salt formed when the two are mixed.
(2) The other cause is the fixing bath. This, for opals and vignetted enlargements especially, should always be fresh and pretty strong, so that the picture will clear rapidly before any deposit has time to take place, as it will be observed that very shortly after even one iron developed print has been fixed in it a deposit of some kind begins to form, so that although it may be used a number of times for fixing prints that are meant to be coloured afterward, it is best to take a small quantity of fresh hypo for every enlargement meant to be finished in black and white. The proportions are 8 oz. to the pint of water.
Almost the only other complaints are traceable to over-exposure or lack of intelligent cleanliness in the handling of the paper. The operator, after having been dabbling for some time in hypo, or pyro, or silver solution, gives his hands a wipe on the focussing cloth, and straightway sets about making an enlargement, ending up by blessing the manufacturer who sent him paper full of black stains and smears. Argentic paper is capable of yielding excellent enlargements, but it must be intelligently exposed, intelligently developed, and cleanly and carefully handled.