THE BRITISH JOURNAL OF PHOTOGRAPHY. March 1, 1864
[Mr. John Spencer, Jun., has been induced to place in our hands the MS. sent to him by Herr Schering. containing some information and remarks upon the preparation of albumenised paper by an improved method; and, as there are also some judicious and useful observations upon printing generally. We have made the following extract. We feel it but just to add that the communication was not written with a view to publication, but simply to put Mr. Spencer in a position to explain the peculiar advantages of the paper to which reference is made --ED.]
I HAVE the honour to lay before you in the following lines some account of an important and substantial improvement in the manufacture of albumenised papers.
After long-continued experiments I have succeeded at last in removing by chemical means, all the impediments which, as you know, rendered so difficult the making of uniformly good albumenised papers.
The most troublesome in the manufacture, and till now the most difficult to remove, was the animal fibrous substance (the fibrine) naturally existent in every white of egg, and not to be removed otherwise than by allowing the collected albumen to set for weeks together, in which process the fermentation produced therein was likewise partially made use of. Then by the time that the purification was carried to such a degree that the albumen could be employed--without leaving behind it on the paper any streaks (of dried fibrine), the white of egg itself must necessarily be partially attacked by the said fermentation and decomposition, and therefore the papers obtained by this proceeding were more or less impregnated with a disagreeable odour in proportion as the albumen had been allowed to set a longer or shorter time, and took part in a greater or lesser degree of the fermentation. .
These volatile products of decomposition, in addition to the disagreeable odour, must moreover naturally act prejudicially in the printing process; and it may be admitted that the greater or lesser quantifies of them contained in the papers have been the principal reason that the manufacturers often received complaints on account of the inequality of their albumenised papers, although they felt persuaded of their being prepared always with the attention demanded by experience, and of the plain paper having been selected with the greatest possible care and caution.
All those organic products of decomposition form with nitrate of silver certain compounds sensitive to light, studied, however, as yet too little to enable their action in connection with chloride of silver and albuminate of silver to be exactly known and regulated for the present.
In order to work up the albumen more easily on photographic papers some have made additions of gelatine, dextrine, ammonia, sugar, and such things; these, however, are (chiefly by reason of the insufficient knowledge we have of their action when connected with nitrate of silver under such conditions) generally even more prejudicial to the albumenised papers than the above-mentioned products of decomposition of the white of egg. Papers with additions of that sort are, on account of the little albumen they contain, generally easy to work with; but, after being printed on, their lustre usually becomes less brilliant, because the deficiency of white of egg the is compensated only by rolling.
The main difficulty in perfecting the fabrication of albumenised The main a papers consisted, in fine, in discovering a means by which we were able to purify large a quantities of albumen in a few days, to such an extent that the least trace of the streak-leaving fibrous substance had entirely disappeared, the albumen not being allowed time to ferment, and no foreign compounds of unknown influence being allowed to pass into the sensitive coating.
From the commencement of my manufacture I have tried to find such a means, and after many fruitless experiments have now completely succeeded in it, so that I will make for the future only papers prepared with pure, fresh, and completely unaltered albumen, and the quantity of chloride found useful by long experience.
I now claim your attention to the fact that the peculiarity and simplicity of the new method of purifying the albumen renders it possible that always an uniform and good product may be sent from my manufactory; and I have secured likewise large supplies of good raw material, in order to be able to work always upon equally good plain papers.
The new albumenised paper exhibits, though not rolled, a surface hard as glass, and a beautifully silky gloss; and has, moreover, only the feeble odour of dried albumen.
The advantages of the new paper being very clear, I do not think it necessary to mention them in detail. Above all other papers it distinguishes itself--firstly, by a greater sensitiveness, so as to enable the photographer to make with it, even in cloudy winter days, a greater number of prints than with other albumenised papers; secondly, the paper may be toned more easily, and fixed more perfectly, than other products; moreover, one needs not fear to lose the whites by strong printing or a somewhat long keeping of the silvered sheets.
That all these advantages of my new paper cannot come out fully and steadily but when the silvering, the drying, and the toning , &c., are made under the necessary rules of experience and caution, I need not explain to practical and scientific men. Since, however, the uniformly good quality of my paper, as I have already observed, is always maintained by the mode of preparing it--since, in other words, the paper is never subjected to the influence of more or less decomposed albumen--it will be, on the other hand, the best test for the fitness, and the good or bad state of the baths employed; that is, if the photographer has the conviction that he may produce good prints on this paper and with good baths.
It is advisable to avoid in the silvering too weak a solution likely to dissolve the albumen, and to avoid keeping the paper in a warm and damp locality. As for the toning and fixing of the prints, I by no means assert that my albumenised papers are only adapted to a few certain methods: they are rather applicable to every rational proceeding, or to one found practical by experience, as has been proved already by numerous experiments.
But in order to satisfy those who wish to get directly a good formula, I will describe in the following the composition of the baths wherewith it is worked in my photographic experimental studio with the best possible results:
|Nitrate of silver||1½ to 2 parts (of weight).|
|Distilled water, (80 to 100 grains to each ounce of water.) 10||10 "|
To this bath are added some drops of acetic acid (till the presence of this acid is recognised distinctly): during the summer more is required than in winter.
The sheet floats three, but it had better float five, minutes; and, as a precaution, the bath of silver is stirred after sensitising each sheet by a glass rod, in order to mix the surface, grown poorer in silver, with the deeper and richer layer; but the mixing may be done also by moving the dish. The drying of the sheet Is done in the usual temperature of rooms (63-77 deg. Fahr.). because, for clear chemical reasons, a higher temperature produces an alteration in the paper with the shutting out of the light, and causes, at the salve time, the loss of the pure whites.
SOLUTION OF GOLD.
(For four sheets.)
|Chloride of gold, pure||4 grains (= 0.25 grammes).|
|Distilled water||4 ounces (= 120 ").|
A solution of one part of bicarbonate of soda is added to ten parts of water as long as the bath shows itself neutral towards blue and red litmus paper. (Too great a surplus of alkaline salt attacks the albumen and diminishes, therefore, the lustre of the prints when finished.) The whole quantity of the liquid is then diluted by adding distilled water to make up eight ounces, and employed after an hour's rest.
For the washing of the sensitised papers it will be very useful to add to the water some hydrochlorate, or some acetate of sodas--that is, where the water is not either river or rain water. In toning, in respect to the temperature, the opposite to that recommended for silvering is to be observed: a constant warmth, not mounting higher than 88 deg. Fah. will always give very fine and equal results. If the solution of gold is allowed to work until its red hue is about to disappear, then a purple black colour always results, giving the copies a nearly stereoscopic effect.
One must never tone with a part of the described bath of gold mere than twelve or fifteen carte de visits together, in order to get the most equal colour possible.
|Hyposulphite of soda||1 part.|
|Distilled water||5 parts.|
.All additions of carbonate of soda, acetate of lead, &c., are not only superfluous but even prejudicial.
I will warn once more those photographers who prefer the employment of weak silver solutions that the more feeble a bath is the greater attention it requires; for it is known that an exchange takes place during the process of sensitising the papers. Chloride of silver is formed as a precipitate in the paper, and nitrate of soda or of ammonia becomes in the same proportion dissolved in the bath of silver. But these newly-formed nitrates prevent with time the complete coagulation of the albumen coating, and may even increase with the age of the bath so as to dissolve the coating of albumen, quite like a weak bath of silver, and to endanger thereby the results; for an incompletely coagulated coating of albumen is not able to fix and to envelope the chloride of silver, the latter being in the state of powder.
By-the-by, the greatest caution is to be used likewise in employing the so-called argentometer, because these instruments naturally cannot mark the quantity of nitrate of silver to a certainty, excepting in a bath of silver not yet used: for in a bath already employed the extraneous salts that have passed into the bath in the sensitising process weigh together with the silver, and therefore it is not possible to make out the true contents of silver salts. It is not intended to assert that the first supplementary additions of nitrate of silver have a very prejudicial influence on the bath, but that the photographer ought to be on his guard not to repeat the additions too often, and that the purer is the bath of silver the more surely fine prints are to be expected.
In consequence of this principle, in my experimental study the silver solution is made in the proportions of one to five, and it is used until nearly three-quarters of the silver (and that may be measured approximately by the number of the sheets silvered) are consumed; then the bath is put aside, the silver precipitated as chloride of silver, and re-changed into nitrate of silver. With this proceeding I have not only to regret no loss of nitrate of silver, but I am likewise always certain of the bath never growing too rich of extraneous and prejudicial salts. In weak baths, or in those grown more feeble, the paper, it is understood, must float a little longer.
I calculate that a sheet of my albumenised paper, including all the losses in the dropping, &c., requires from forty to sixty grains of nitrate of silver.E. SCHERING.