This is perhaps the most satisfactory of all processes, and may be effected by bleaching the print in a solution of mercuric chloride, and then re-developing with an old, used ferrous-oxalate de-veloper.
Intensifying or tonitig with Monckhoven's Silver Cyanide. The objection to the use of this formula is that one cannot make sure of obtaining a black tone in the intensified print, the colour of the image tending towards a brown.
Intensifying with Silver. It may be quite possible to intensify bromide prints with an acid silver and iron, or acid silver and pyrogallol intensifier; but we, so far, have been unable to obtain results free from stains.
Intensifying or toning with Uranium. The application of Selle's process of uranium intensification, first suggested for collodion negatives in 1865, has been suggested as a toning process for bromide paper, but it is purely an intensification process. The following formula, which is a modification of the original one, acts well: -
Potassium ferridcyanide ... ... ... 1 part.
Uranyl nitrate ... ... ... ... 1 ,,
Acetic acid ... ... ... ... ... 20 parts.
Distilled water ... ... ... ... 200 ,,
The print, when perfectly free from hypo, should be soaked in water till limp, and then the above solution applied. When the intensification has proceeded far enough, wash thoroughly for half an hour in water acidulated with acetic acid.
Intensifying or toning with Copper Ferricyanide. This method gives a wide range of tones through various tints of brown and reddish-brown to brilliant red. The well-washed prints are immersed in the following solution, which should be freshly prepared.
Neutral potassium citrate ... ... 140 grs.
Crystallised copper sulphate ... ... 20 ,,
Potassium Ferricyanide ... ... 9 ..
Water ... ... ... ... ... 8 fluid ozs.
First dissolve the citrate, then the copper, and finally the ferricyanide. The prints should be kept in motion during the action of the toning bath, and when the desired tone is obtained they should be thoroughly washed.