It is sometimes desirable to produce a positive upon paper in much less time than is possible by the ordinary process, in which manner it takes not less than 12 hours to complete a good photograph. The following process possesses some interest.
Distilled water .. .. 125 dr.
Citric acid ...... 7 1/2 dr.
Iron and ammonia citrate 4 dr.
Conc. liq. ammonia .. 7 1/2 dr.
After shaking the bottle until everything is dissolved, the solution is filtered. Now fasten a piece of positive paper with clamps upon an even board, and cover the same with the above solution, applying a flat camel-hair brush up and down the paper, until it is evenly coated, after which manipulation it should be dried in the dark.
The paper prepared in this manner will have a deep yellow tone. The printing is done, as usual, in a printing frame; but care must be taken that the action of the light commences simultaneously with the copying. The exposure should be very short, and continue only until the principal lines of the picture are visible. After this, the picture is placed in a flat dish, the exposed side up, and then moistened with distilled water, when the following developer is to be poured upon it: -
Distilled water .. .. 125 dr. Cryst. silver nitrate .. 4 dr. Conc. liq. ammonia .. 2 dr.
This solution must be filtered, and will, after application, bring out all the details of the picture, but with a disagreeable red tone. (This developing solution, by shutting off the light, can be kept for a long time, and, by filtering again when wanted, can be used repeatedly.) Afterwards the picture is carefully washed in running water, and fixed in the following bath: -
Distilled water...... 125 dr.
Soda hyposulphite .. .. 7 1/2 dr. Aqua regia ...... 2 1/2 dr.
In this bath the picture remains several minutes, until it has changed to a* deep purple tone, after which it is put into a dish with warm water, and washed, and then rinsed 3 or 4 times in a change of water. Now it is placed between a few sheets of blotting-paper, and then dried over a spirit lamp. According to the quantity of aqua regis and soda hyposulphite in the fixing bath, the tone can be changed. The tone can likewise be modified by adding a little pyrogallic acid. This copying process can be also used for enlargements.