Photo-engraving, Photo-etching and Photo-lithography in Line and Half-tone / Also Collotype and Heliotype

by W. T. Wilkinson

The silver solution named above, is suitable for negatives of subjects in line, but for the production of negatives with delicate half tones, such as portraits, landscapes, or of the many subjects which are photographed direct, then it will be necessary to provide another bath solution, made and managed in the same way, but only containing sufficient nitric acid to just redden litmus paper, as a bath gives the finest half-tones when nearly neutral, or only slightly acid. It should be remembered that the deepest shadows are represented by clear glass in the negative, to insure which would be impossible with the silver solution inclining ever so slightly toward alkalinity.

The nitrate of silver bath may be made up with distilled water, if pure—that is, if the water is bona fide distilled and not merely from waste steam; if this cannot be guaranteed, the best plan will be to get a gallon of tap water, dissolve in it one ounce of nitrate of silver, then add saturated solution of bicarbonate of soda, until an alkaline reaction to litmus paper takes place, then place the lot in white glass bottles, and expose to the action of light for three or four days. During that time the solution will, first of all, turn black, and then will gradually become quite clear, the organic matter—which if not removed, would have caused trouble—falling in a black mass to the bottom.

Now filter the purified water and use it for compounding the nitrate of silver bath, but do not use it for any other purpose.

The strength of a nitrate of silver bath, for line work, should be thirty grains of nitrate of silver to each ounce of water, and should not be allowed to fall below twenty-five; and for half-tone negatives, nitrate of silver should be thirty-five, and not lower than thirty grains to the ounce.

Be sure to keep all funnels, bottles, and dishes used for the silver bath, separate and distinct from all others, and never use them for any other purpose. {14}

THE NITRATE OF SILVER BATH (2).

In the ancient days of photography, when, to say it was possible to prepare a dry plate nearly as sensitive as a wet collodion plate, was to excite the risible faculties of the audience, the above heading might almost always be seen in the journals, and the amount of matter written under that heading would fill many good-sized volumes. Some writers went into the subject in a very elaborate manner, whilst others would counsel very simple methods of preparation and management.

The directions given above for making a bath solution for line negatives, will, if carried out carefully and cleanly, at once yield a solution giving good negatives. After the bath has been mixed, either with distilled water, ordinary tap water (in iron districts tap water should not be used), or water that has been sunned and filtered, as soon as the bulk has been made up to the eighty ounces, the solution should be put away all night before it is tried, then in the morning filter it carefully through a pledget of cotton-wool stuffed loosely in the neck of a perfectly clean funnel, into a perfectly clean bottle or jug, which must be kept entirely for use of the silver solution. When the bath solution has been filtered it should be perfectly clear; if it is at all cloudy or turbid, the filtration must be repeated.

When the solution is perfectly clear and bright, pour sufficient into a perfectly clean porcelain, glass, or papier-maché dish, then take a clean plate (polished, or albumenized) and coat it with collodion; close the door of the dark-room, and when the film of collodion is perfectly set, raise one end of the dish containing the silver solution, place one edge of the collodionized plate against the bottom of the upper edge of the dish, then drop the plate upon the bottom of the dish, and at the same time lower the dish; by this means the silver solution will flow in an even wave over the surface of the collodionized plate; now place the cover on the dish so as to exclude light and dust, and allow the plate to remain in the solution for five minutes, then with a silver hook lift the plate from the solution, and allow it to drain (remember that no light must get into the dark-room except what is filtered through either two thicknesses of golden fabric, or one of canary medium); when the plate has drained so that no solution drips from it, place it into the carrier of the dark slide; then close the dark slide and let it remain there for five minutes, at the end of which time remove the plate to the sink, and flood it with sufficient developer (page [17]) to just cover the film; keep this solution flowing, to and fro, over the {15} plate for the space of two minutes, then wash it under the tap until the surface is no longer greasy; then apply the fixing or clearing solution (page [17]) until the whole of the yellow bromo-iodide is dissolved away; again wash, and take the plate into the daylight.

Now comes the test; if the film is perfectly transparent, and clear as the glass itself, the bath is all right; but if there is the slightest deposit (which can be removed by lightly rubbing the finger along the surface of the film), then the solution will require the addition of a little nitric acid. After this stir it well, and after a rest of an hour or two try again, repeat the addition of the nitric acid, and try a plate; repeat until the film, after developing, washing, and fixing, is perfectly clear, and free from deposit and fog.