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Tuesday, 29 March 2011
Early in the history of photography conservation, cracks were a tool to identify albumen photographs.
Exposure to Moisture Causes Changes in Albumen Prints
The process is as follows : Sensitise the paper as usual on a nitrate of silver bath, at 20 per cent., and print in the ordinary way; only, it is better to overprint it a little. Then place the proof in a dish of water in order to free it from the greater part of its nitrate; put it, afterwards, in a dish of salted water, and leave it there from five to ten minutes. The object of this bath is, to convert every trace of free nitrate that might have been left in it by the first bath into chloride. This bath is essential to prevent the decomposition of the following bath, in which the proof is to be next placed. This bath is composed as follows :
Sesquichloride of gold
Phosphate of soda (the purified tribasic phosphate of commerce)
N.B. This bath ought to be completely neutral, or, at all events, rather alkaline than acid. If it should be acid, it is a sign that the chloride of gold was not properly prepared.
As soon as placed in this bath, the tone of the proof begins to change, and passes rapidly from red to purple, violet, and black; at the same time, the solarised parts of the proof lose their dead tone, and all their details are developed in an astonishing manner.
The colouring may be arrested at any moment. If it be stopped at the purple tone, the proof will appear sepia after the operation, if stopped at the black tone, it is rather black or grey. After this bath, the proof is put in a new hyposulphite of soda bath, of 20 per cent., in which -a little Spanish white has been put in suspension, and finished as usual.
These proofs are so stable that they resist the action of a cyanide of potassium bath for a very long time.
The great advantages of this process are:
1. The colouring bath is perfectly neutral, and cannot produce any decomposition in the hyposulphite of soda; 2. The colour is entirely produced by the gold, which has hitherto been considered the most certain means of colouring, since the proof is not in contact with the hyposulphite until after it has received its colour. Finally, there does not exist in the bath any organic acid to determine its spontaneous decomposition, and the precipitation of the gold in a metallic state.
The colouring bath described above may be prepared beforehand, it does not decompose by keeping if care be taken that none of that used is returned to the bottle. It is likewise very economical, since with 15 grains of chloride of gold, sixty or seventy pictures, 24 X 30, may be coloured. In order to make sure that no traces of gold that may be left in the bath after use shall be lost, the remains of these baths should be poured into a bottle containing some bits of copper.