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Photographic Printing (Sensitive papers ought not)

Sensitive papers ought not to be exposed in the frame until they are quite dry. The shutter at the back of the frame is removed, and the negative laid flat upon the glass, collodion-side uppermost. A sheet of sensitive paper is then placed upon the negative, sensitive-side downwards; next comes a layer of thick felt; and the whole is then tightly compressed by replacing and bolting down the shutter. The amount of pressure required is not very considerable, but if the springs of the frame become too weak after a time, a few pieces of mill-board may be placed beneath them.

The time of exposure to light varies much with the density of the negative and the power of the actinic rays, as influenced by the season of the year and weather.

If the exposure to light has been correct the print appears slightly darker than it is intended to remain. The toning bath dissolves away the lighter shades, and reduces the intensity, for which allowance is made in the exposure to light. A little experience soon teaches the proper point; but much will depend upon the state of the toning bath, and albuminized paper will require to be printed somewhat more deeply than plain paper.

If, on removal from the printing-frame, a peculiar spotted appearance is seen, produced by unequal darkening of the chloride of silver, either the nitrate bath is too weak, the sheet removed from its surface too speedily, or the paper is of inferior quality.

If, in the exposure to ordinary diffused daylight, the shadows of the proof became very decidedly coppery before the lights are sufficiently printed, the negative is in fault. Ammonio-nitrate paper highly salted is particularly liable to this excess of reduction, and especially so if the light is powerful. Toning.

The print should be first washed in common water until the soluble nitrate of silver is removed. This is known to be the case when the liquid flows away clear; the first milkiness being caused by the soluble carbonates and chlorides in the water precipitating the nitrate of silver. Ten minutes in water running slowly from a tap will be sufficient to cleanse a print from nitrate of silver; or three or four changes in a dish, pouring off quite dry between each change. It is an advantage to finish off with a solution of salt (2 grs. to the oz.). Pour the toning bath out into a flat dish, and put the prints into it 2 or 3 at a time, wards to secure a constant movement. Continue to keep the prints moving, and watch the changes in color.

If the prints are removed as soon as the blue color of the gold is seen, they will usually change in the fixing bath to a warm shade of brown; but when left for 2 or 3 minutes longer in the toning bath, the darker tint becomes permanent.

Fixing.

One oz. of hyposulphite of soda dissolved in 6 oz. of water would fix two batches of stereoscopic prints, 20 in each batch. Allow the prints to remain in the fixing bath for 20 minutes, with occasional movement, after which they may be transferred to a dish of clean water. Washing.

It is essential to wash out every trace of hyposulphite of soda from the print, if it is to be preserved from fading, and to do this properly requires care.

Always wash with running water when it can be obtained, and choose a large shallow vessel exposing a considerable surface in preference to one of lesser diameter. A constant dribbling of water must be maintained for 4 or 5 hours, and the prints should not lie together too closely, or the water will not find its way between them.

When the prints have been thoroughly washed, blot them off between sheets of porous paper and hang them up to dry.

Mounting.

Mount the proofs with a solution of gelatine in hot water, freshly made; gum-water, prepared from the finest commercial gum, and free from acidity, may also be used, but it should be made very thick, so as not to sink into the paper, or produce "cockling up" of the cardboard on drying.

Positive Printing by Development.

Negative printing processes will be found useful during the dull winter months, and at other times when the light is feeble, or where it is required to produce a large number of impressions from a negative in a short space of time. The proofs, however, as thus obtained, are not equal to direct sun-prints in beauty and gradation of tone.

Take of iodide of potassium, 120 grs.; bromide of ammonium, 30 grs.; water, 20 oz.

Float the paper on the iodizing bath until it ceases to curl up, and lies flat upon the liquid: then pin up to dry in the usual way.

Render sensitive upon a bath of aceto-nitrate of silver, containing 30 grs. of nitrate of silver with 30 minims of glacial acetic acid to each oz. of water.

Place the dried sheets in contact with the negative in a pressure frame, and expose to a feeble light. About 30 seconds will be an average time upon a dull winter's day, when it would be impossible to paint in the ordinary way. Develop by immersion in a saturated solution of gallic acid. After the picture is fully brought out, wash in cold and subsequently in warm water, to remove the gallic acid, which, if allowed to remain, would discolor the hyposulphite bath. Fix the print in a solution of hyposulphite of soda, one part to two of water, continuing the action until the yellow color of the iodide disappears. Wash thoroughly in plenty of water.

Negative Printing Process upon Chloride of Silver.

To salt the papers, prepare the following solution: Chloride of ammonium, 100 grs.; citric acid, 56 grs.; sesquicarbonate of soda, 66 grs; gelatine, 40 grs.; distilled water, 20 oz. Float the sheets for 1 minute; render sensitive upon a bath of aceto-nitrate of silver. Take of nitrate of silver, 30 grs.; glacial acetic acid, 30 minims; water, 1 OL. Float the papers upon this bath for 3 minutes, and suspend them to dry. The exposure to light is conducted in the ordinary printing frame.

The developing solution is prepared as follows:

Gallic acid, 2 grs.; water, 1 oz. Filter through blotting-paper, to remove floating particles, which woull produce spots in this process; pour the solution of gallic acid into a flat dish, and immerse the prints, 2 or 3 at a time, moving them about, and using a glass rod to remove air-bubbles; wash the prints for several minutes in 1 or 2 changes of water, in order to extract the gallic acid; tone in bath of chloride of gold and phosphate of s soda; fix in hyposulphite, and wash.