PREPARATION OF PAPER FOR PRINTING.
Ammonia Nitrate Paper.
In the first place, the paper chosen for the purpose should be cut to the size required, and a pencil mark put in one corner to denote the right side of the paper. I prefer for this kind of printing the French positive paper, Canson Freres. It gives, very distinctly, the most delicate lines of the negative, and the high lights are preserved clear and bright. The first wash may be either with common salt, muriate of ammonia, or muriate of baryta, indifferently. The bath should be of the following strength:
160 grains chloride of sodium. 20 ounces water.
The several sheets of paper are immersed, one by one, in this bath, taking care that each sheet is entirely covered with liquid, and that no bubbles of air remain on the surface. The number of sheets that can be soaked in the bath at one time must depend on the depth of liquid in the bath. Let the paper remain in the bath at least one hour; in which time it will have imbibed the liquid sufficiently. Each sheet should be removed separately, and, after draining for a few seconds, should be hung up by one corner against the projecting edge of a shelf to dry, care being taken that the sheets of paper do not touch each other.
When dry, place them in a paper case, under pressure, ready for the next operation. The same bath may be used several times, if protected from dust, as it does not become injured by keeping.
This is to render the paper sensitive to light, and should be conducted in a darkened room. Dissolve 30 grains of crystallized nitrate of silver in one ounce of water, then add, drop by drop, a solution of ammonia, until the brown precipitate of oxide silver at first thrown down is re-dissolved.
To ensure success in this operation, and to prevent an overdose of ammonia, the silver solution should be shaken after the addition of each drop of ammonia; towards the end of the operation the ammonia should be added very cautiously, to avoid overstepping the desired point, that is, just to re-dissolve the precipitated oxide.
The paper may be excited either by floating on the surface of the ammonia nitrate of silver solution, or by application with a glass rod or cotton brush on the marked side. With the former mode, the nitrate of silver is poured into a flat porcelain dish to the depth of one-sixteenth of an inch ; the paper, with the marked side downwards, is gently placed on the surface of the liquid. It should be raised once or twice from the silver solution, to remove the bubbles of air. Three minutes floating on the bath will be sufficient. To remove the paper from the bath, first gently raise one corner with a strip of glass, lift it up carefully, and allow it to drain for a few seconds; then hang to dry.
When dry, the sheet of paper is placed in the pressure frame, sensitive side downwards, in contact with the negative picture; pressure is applied, and the printing frame removed into the light. The time for exposure will vary according to the brightness of the day, and the density of the negative- Experience alone can determine this point; it is, however, better to slightly overprint than otherwise, as the excess of blackening can be removed with advantage by immersion in a strong hypo-sulphite bath; but, on the other hand, it is not so easy to remedy a faint print.
Hypo-sulphite soda bath, 1 ounce hyposulphite of soda 1 pint water. To this solution add a portion of chloride of silver, prepared in the following manner:,take one ounce of nitrate of silver solution (30 grains of nitrate of silver to 1 ounce of water), add 40 grains of common salt: a precipitate of chloride of silver is immediately thrown down. When this is settled, the liquid above is poured off; fresh water is added several times to wash the precipitate, which is then poured into the hyposulphite solution, and is immediately dissolved.
On removal from the pressure frame the printed copy is at once placed in the hyposulphite bath. If well printed it should remain in half an hour; if overprinted a longer time is necessary, until the excess of printing is cleared off. This fixes the picture, and renders it insensible to light. Finally, it is necessary to wash the drawing thoroughly, to remove every particle of hyposulphite from the paper. To do this effectually, place the drawing in water, which should be changed several times. The last wash should be with hot water, to make quite sure that the hypo-sulphite of soda is entirely removed.
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