THE PHOTOGRAPHIC NEWS. Volume 10, No. 396, April 6, 1866, p.163
THE aim of those who prepare albumen, &c., paper for photographic purposes, appears to be that of manufacturing art article that will absorb the least amount of nitrate of silver, and still produce a good picture. This aim is, naturally, very praiseworthy. But all attempts will be futile, or, at least, will be likely to be so, unless the manufacturer has a succint and well-defined notion of that which he desires to accomplish, and of the means in art and science that might probably effect his purpose. To experiment with any solution that may by accident be placed before him, or occur to his thoughts, would be equivalent to fishing in the sea for pearls with a bent pin.
It is our intention to offer some hints on this subject for the benefit of those who are interested, and then leave the latter to' devise proper methods for effecting the, ends in view.
If albumen paper, such as is now in the market, be floated on a solution of nitrate of silver, it is a fact that this solution traverses the albumen film, and penetrates the texture of the paper.
This is a well-known fact. To prove this, it is necessary simply to place the back of such paper upon the negative, and to expose the same to sunlight. A picture will soon be visible in the paper, but scarcely at all visible on the albumen film.
This experiment testifies to two facts simultaneously; the first is, that the soluble chlorides in the albumen penetrate the texture of the paper; and that, secondly, the nitrate of silver follows their example.
But if thin plates of glass, mica, porcelain, &c., were substituted -for paper, we know well that neither of the above-mentioned solutions proceed further than the surfaces of these materials. We are justified, therefore, in concluding that less both of the soluble chlorides and of nitrate of silver will suffice to produce the act of sensitization in the latter case than would be required if paper were used.
What percentage of nitrate of silver would be sufficient to sensitize a chlorized albumen film on glass, mica, &c.?
A solution containing five grains of nitrate of silver to the ounce of water would effect the purpose in -three minutes; whereas, ten times this quantity would be required with most of the papers in commerce. The chlorides -in the albumen vary in strength in the same proportion and for the same reasons.
A question, therefore, is immediately suggested.
Can paper be sized, or otherwise prepared afterwards, as to possess a vitreous or micaceous surface, which shall prevent the solutions in question from penetrating the texture beneath?
We entertain the opinion that this object can be effected; and we furthermore think that it has already been effected in certain papers for special purposes ; for instance, in. that prepared for the Wothlytype.
Paper, without sizing or with a comparative small quantity of sizing, is bibulous ; that is, it is in a condition for absorbing or imbibing liquids ; and, it would appear, that the greater the amount of sizing in paper, the less is the capillary attraction in the fibrous pulp that constitutes the mass of paper. Hence, it seems right to apply more sizing to photographic paper than for that which is used for the ordinary purposes of life ; and, furthermore, it is probable that we may eventually devise some substance or mixture of substances that will subserve the purposes more effectually.
In the first place, then, let us place before us categorically the different sorts of sizing used in the manufacture of paper, and thus study the individual and combined action of the components.
In Ure's Dictionary the reader will find the following quotations
"When the paper is dry, it is taken down, and laid neatly in heaps to be sized. Size is made of pieces of skin, cut off by the curriers before tanning, or sheep's feet, or any other matter containing much gelatine. These substances are boiled in a copper to a jelly, to which, when strained, a small quantity of alum is added. The workman then takes about four quires of paper, spreads them out in the size properly diluted with water, taking care that they be equally moistened. This is rather a nice operation. The superfluous size is then pressed out, and the paper is parted into sheets."
The preceding quotation refers to paper manufactured by the hand; but the principle remains the same in machine paper.
"Formulas for Paper Size.
" Dry paper stuff
Resin, previously dissolved in 500 grammes of carbonate of soda
"To 100 parts of dry stuff, properly diffused through water, add a boiling uniform solution of eight parts of flour, with as much caustic potash as will render the liquor clear. Add to it one part of white soap previously dissolved in hot water. At the same time heat half a part of resin and the requisite quantity of weak potash lye for dissolving the resin; mix both solutions together, and pour into them one part of alum dissolved in a little water.
"Those who colour prints, size them previously with the following composition: Four ounces of glue, and four ounces of white soap dissolved in three English pints of water. When the solution is complete, two ounces of pounded alum must be added, and as soon as the composition is made homogeneous, it is ready for use. It is applied cold with a sponge, or rather with a flat camel's hair brush. Ackermann's liquor, as analyzed by Vauquelin, may be made for sizing paper as follows
Resinous soap ...
"The soap is made from 48 kilos. of pounded resin and 2~22 crystals of carbonate of soda, dissolved in 100 litres of water. It is then boded, till the mixture becomes quite uniform; the glue, previously softened by twelve hours' maceration in cold water, is to be next added; and when that is totally dissolved, the solution of alum in hot water is poured in. Three quarts of this size were introduced into the vat with the stuff, and well mixed with it."
The preceding quotations are quite illustrative of what we wish to suggest; they show plainly what substances are used to prevent paper from imbibing moisture. Neither glue nor starch alone, however, although they may fill up all the pores of the paper, and cause adhesion to the different parts, would attain the end in view, because they are both soluble; but resin dissolved in an alkali and mixed with starch, renders the latter insoluble; in like manner, gelatine or glue is rendered insoluble by a solution of alum, by the formation of a species of leather, as is practised in certain branches of tanning.
The same end might be obtained by mixing in the dark room a bichromate of an alkali with the gelatine solution, and then sponging the paper with this solution, or floating the paper upon the solution By exposing the sheets afterwards to light, the gelatine film becomes insoluble, and consequently impervious to moisture.
A solution of tannic acid may in like manner be used for converting the gelatine into an insoluble condition.
There is sufficient in this exposition about the sizing of paper to show not only what is required to render the surface of paper almost impermeable to fluids, but also the absurdity of obtaining patents on such flimsy grounds. Patents have been applied for by which the sole rights of rendering paper thus impermeable--In fact, of sizing paper a little more than usual--are to be secured to parties who aim to make money out of photographers by the silliest pretences. Look to your rights!