SearchAbout This SiteTreatment ForumVideo clipsGalleryScienceLibraryTechnology

Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9

Chapter XV.

NOTHING can be easier to prepare than the bath of nitrate of silver, and yet there is no preparation in the art of photography which produces so many difficulties and troubles to surmount as the sensitizing bath for the iodized or bromo-iodized collodion plates. In consequence of this it becomes a difficult task to prescribe rules by which such a bath can be preserved sensitive under the troubles with which it is so frequently beset. The origin of these troubles maybe traced to the materials introduced by the immersion of the collodion plates; but these deteriorating materials are of such a heterogeneous nature, arising from the decomposition of the pyroxyline, of alcohol, of ether, of the iodides, the bromides, their bases, and of the elements combining with them, that it is as yet an unsolved problem, that of determining precisely the cause of any given abnormal action in the nitrate bath. It is true, as regards the introduction of injurious substances into the bath, all effects resulting therefrom can be avoided by using the solution of nitrate of silver only once. If this salt were not so expensive, this mode of avoiding trouble would be by far the wisest and the safest. In such a case the photographer would flow his plate with the silver solution in the same manner as with the developing or fixing solution, using just sufficient to cover the film and to sensitize it. All the residual part might be collected, decomposed, and fresh nitrate prepared. But because the silver salt is a dear material, we aim to economize by using the solution over and over again. For this purpose, glass, porcelain or photographic-ware baths are constructed for containing the fluid. They are made so as to accommodate the largest plate with the least quantity of the solution, a great mistake superinduced by false economy. In this country vertical baths seem to be the only ones employed; whereas in France and Germany, for economical and other special reasons already alluded to, horizontal dishes contain the solution, and the plates lie, as it were, collodion side downward in a thin layer of the same. Some of these baths are especially adapted for the tourist, admitting the fluid to be closed hermetically by means of India-rubber caps, screws and clamps. Nitrate of silver will permeate through the parietes of porcelain baths; the photographic-ware bath and the glass are not subject to this inconvenience.

Preparation of the Sensitizing Solution.

An ounce Avoirdupois contains 437.5 grains; the druggists and photographic dealers retail all their chemicals according to this weight, and not, as many suppose, according to the Troy weight, of which the ounce contains 480 grains. The sensitizing solution is found by experience to be sufficiently strong if it contain from 35 to 40 grains to the fluid ounce of water, or from 8 to 10 per cent.

Formula No. 1.

Nitrate of silver, (recrystallized,) 3 ounces.
Distilled or pure rain-water. 36 ounces
Washed iodide of silver 6 grains.
Washed oxide of silver 6 grains.

Dissolve the nitrate of silver in half the water, then add to it the washed iodide of silver, prepared as directed on a preceding page, afterward add to the mixture the six grains of oxide of silver, which is prepared as follows: Take a solution of ten grains of nitrate of silver and drop into it a solution of pure caustic potash, as long as a brown precipitate is formed. Then filter and wash the brown oxide on the filter many times with cold water, and afterward with warm water, until the filtrate ceases to have any action on red litmus paper.

The mixture is now boiled in a large glass flask on a sandbath, and when cold the remaining water is added to it, and the whole of it is filtered through a double filter of Swedish filtering paper. The solution so prepared will be saturated with iodide of silver, so that it will not dissolve any of the iodide of silver on the collodion film; it will be besides perfectly neutral, if the oxide of silver bas been thoroughly washed from any adhering alkali. With a collodion containing free iodine, either from decomposition or by insertion, this bath is exceedingly sensitive, and produces at the same time clear pictures. For colorless collodions it is not suitable, nor for collodions which are quite freshly made, without the addition of iodine, that is, for those which have not had time to ripen, as it is termed in ordinary language.

For such collodions, the colorless and pale colored collodions, containing, as they generally do, cadmium salts, the following bath will be found to be quite effective in producing good results

Formula No. 2.

Nitrate of silver, (recrystallized,) 3 ounces.
Distilled or rain-water 36 ounces.
Iodide of silver, (washed 6 grains.

Mix as before, and filter without boiling. For each ounce of nitrate of silver add one drop of nitric acid. This amount will probably be found sufficient to produce a clear picture; should the picture show any signs of fogging, add another drop, and so proceed until the details of the development appear without a universal cloudiness over the plate.

Formula No. 3.

Nitrate of silver, (recrystallized,) 3 ounces.
Distilled, or pure rain-water 36 ounces.
Iodide of silver, (washed,) 6 grains.

Prepare as before, and after filtration divide the quantity into two lots of 18 ounces each. Neutralize one of these with washed oxide of silver by boiling, and then filter. Add to the other 18 drops of a solution of acetate of soda, (containing 160 grains to the ounce of water,) and 10 drops of glacial acetic acid. Each of these baths may be used separately, or in mixture. The neutral bath is kept neutral without admixture; but to the second, containing the acetate of soda and acetic acid, a portion of the first may be added as required from time to time, if it is found to work too slowly. As a general thing the acetate of soda bath produces very vigorous pictures, and renders the collodion film quite sensitive.

In summer the bath need not be so strong in nitrate of silver as given in the preceding formulas. Six or seven grains of silver per cent of the water will be sufficient when the temperature is high; on the contrary, from eight to ten per cent may be used when the temperature is moderate or low. The sensitizing solution works quicker when warm than when cold.

When the sensitizing solution becomes weak by exhaustion, it can be restored to a good working condition by the addition of a stronger solution of nitrate of silver, containing 40 or 50 grains to the ounce of water. After a bath has been in operation for some time, it becomes saturated with a variety of impurities, such as ether, alcohol, acetic acid, aldehyde, the various nitrates in the collodion, and a variety of substances arising from the decomposition of this heterogeneous mixture. The best way to get rid of all volatile material is to subject the solution to distillation, until all the ether and alcohol, at least, have been expelled, and then to filter the residue in the retort, and to mix it with anew bath. Although such a restored bath will give good results for a while, it soon gets out of order, and can no longer be relied upon. In such a case it is far more expedient to set it aside for reduction, and to form a totally new bath, than to be at the trouble of a second distillation, because the fixed salts have accumulated to such a degree as to render the bath very capricious and unstable.

When a bath does not yield clear pictures when first formed, or ceases to do so after a given time with the same collodion, or happens not to do so with a new collodion, it is advisable not to trifle with the bath by adding either acid or alkali. It may be well to ascertain by test-paper whether the trouble is attributable to alkalinity or acidity. If no alkali has been added to the bath, it will probably have an acid reaction. In this case it is preferable to boil the bath with the washed oxide of silver, as before prescribed, and then to filter it. Should the bath turn out to be neutral to test-paper, it will be found in general a better practice to add a few drops of tincture of iodine to the collodion, rather than to acidify the sensitizing solution; because the iodine in the collodion liberates an acid by decomposition on and in the film of collodion, which rectifies the evil where the rectification is wanted, and at the proper time, without changing materially the conditions of the bath. Thus the operator will learn to use up a highly colored collodion by mixing it gradually, as it is wanted, with new and almost colorless collodions, in order to clarify his pictures, without resorting to methods of attaining to the same result by adding acid to the bath.

During the time the bath is in use, a quantity of insoluble material of a gray or violet-gray color is precipitated on the bottom and sides of the bath, and frequently floats about in the sensitizing fluid. The particles of this material, as well as of the acicular crystals of acetate of silver in a weak bath are apt to attach themselves to the moist collodion film on its immersion, and thus give rise to the innumerable small apertures sometimes exhibited on the developed negative. These particles are not the sole cause of this evil, so much dreaded; but they frequently cause it by their attachment to the film during the exposure, and owing to their opacity, prevent the actinic action from taking effect on the film beneath, and becoming loosened by the developing and fixing solutions, afterward expose the transparent parts on which they had rested. It is advisable, therefore, to expose the bath in a glass vessel to the rays of the sun as often as possible, in order that the organic matter may be precipitated. The bath, too, ought to be filtered very frequently in the same filter, at least once a week; anti if every evening, so much the better. After filtration the bath can be strengthened by an addition of fresh solution, in proportion to the daily work performed. See, during filtration, that the sides and the bottom of the vessel are perfectly clean before the solution is poured back again. A long thin wooden spatula, with a piece of sponge at the end, will be found very convenient for clearing away the adhering gray deposit. Use only rainwater for rinsing; rinse thoroughly; then turn the bath wrong side up, and rear it on one corner, in order that every drop of water may thus be removed. Wipe the edges before the sensitizing fluid is again introduced. This exposure to the rays of the sun, and frequent filtration will remedy in a great measure the trouble alluded to, and there is no fear of injuring the property of the solution, for nitrate of silver alone is not acted upon by light, does not change at all when pure.

By exposing the solution in a vessel, such as a glass evaporating dish, much of the superfluous ether and alcohol will pass off in vapor, and thus produce a remedy for another evil which an old bath invariably gives rise to, namely, that of causing oily-looking stains and streaks on the surface of the film.

Where the trouble of recrystallizing the nitrate of silver would be deemed too great, and neutral nitrate of silver can not easily be purchased, I would recommend that the photographer should fuse the nitrate of silver in a porcelain evaporating dish, at a gentle heat, and afterward pour out the fused mass on a silver or marble plate, as directed in the manufacture of lunar caustic. The same proportions of the fused nitrate are used as in the formulas for the recrystallized nitrate. Or a strong solution of the nitrate may be boiled with the washed oxide of silver, filtered, and evaporated to dryness, and used in the same way.

Home ~ Library ~ Science ~ Technology ~ Gallery ~ Video ~ Forum ~ About ~ Search