Mercury intensifier for film and plates giving increased maximum density with little intensification of intermediate tones. Also known as Monckhoven’s intensifier. The mercury intensifier is recommended where extreme intensification is desired but where permanence of the resulting image is not essential. If permanence is essential either the chromium or silver intensifiers should be used.

After hardening in SH1 and washing, bleach the negative in the following solution until the image turns white; then wash thoroughly:

Potassium bromide22.5
Mercuric chloride
Water to make1liter
Dissolve chemicals in order.

The negative can be redeveloped or blackened with 10% sodium sulphite solution; or with a developer such as D72 (diluted 1:2) or D16; or with 10% ammonia (28% ammonia diluted 1:9). These solutions give progressively greater contrast in the order listed. To increase contrast considerably, treat with the following solution after bleaching:

Solution A
Silver nitrate crystals22.5
Water to make
Solution B
Sodium cyanide15grams
Potassium cyanide15grams
Water to make500mililiters
Mix chemicals in order.

To prepare the intensifier, add the silver nitrate Solution A to the potassium cyanide Solution B until a permanent precipitate is just produced; allow the mixture to stand a short time and filter. Redevelopment cannot be controlled as by the chromium method but it must go to completion.

Warning:Cyanide is a deadly poison and should be handled with extreme care. Use rubber gloves and don’t expose yourself to its fumes. It reacts with acid to form poisonous hydrogen cyanide gas. When discarding a solution containing cyanide, always run water to flush it out of the sink quickly. Cyanide solutions should never be used in poorly ventilated rooms.

Stains are sometimes produced during intensification unless the following precautions are taken:

  1. The negative should be fixed and wash throughly before treatment and be free of scum or stain.
  2. It should be hardened in the formalin hardener before intensification treatment.
  3. Only one negative should be handled at a time and it should be agitated throughly during the treatment.
  4. Following the treatment, the negative should be washed throughly and wiped off carefully before drying.