Kodak IN-1 Mercury Intensifier
Potassium bromide - 3/4 oz. avdp. - 22.5 g - 7/8 oz. avdp.
Mercuric chloride - 3/4 oz. avdp. - 22.5 g - 7/8 oz. avdp.
Water to make 32 U.S. fl. oz. - 1L - 40 Imp. fl. oz.
[Native measurements listed first. Accuracy to within 250mg, 25ml, 1/8 oz.]
Bleach the negative in this solution until it is a creamy white color and then wash it thoroughly. After this treatment, the negative should be blackened or "redeveloped" in a 10 percent solution of sodium sulfite, or in a developing solution such as D-72 diluted one to two, or in a 10 percent ammonia solution--one part concentrated ammonia to nine parts of water. These solutions give progressively greater density in the order given.
Many photographic intensifiers depend on the use of mercury, but experience has proved that mercury-intensified images are not as stable as images produced by chromium intensification.
When the silver image is placed in a solution of mercuric chloride, a reaction with the silver takes place and a mixture of mercurous chloride and silver chloride is formed. The bleached image, which appears white, can then be treated in various ways. If it is redeveloped, for instance, both the silver chloride and mercurous chloride will be reduced to the metals--silver and mercury. So, in addition to the silver with which you started, there is now added to every part of silver a proportionate part of mercury. Instead of using a developer, you may blacken the image with ammonia to form a black mercury ammonium chloride which gives a high degree of intensification.
Skull and crossbones! Mercuric Chloride or mercury bichloride (also commonly known as corrosive sublimate) is a very poisonous salt and should, therefore, be handled with the utmost care.
Use of some sort of fume hood or ventilation system is also recommended.