by dannybee » Mon Apr 24, 2017 12:46 pm
its in a really old book "How to make old-time photos" it states
sensitivity can be increased threefold by adding , to a bichromated colloid layer, a metal salt which precipitates on contact with a chromate but not with a bichromate. In this situation, the metal salt, itself, does not contribute to the tanning action. rather, it reacts with the neutral chromate which is formed during exposure and increases the tanning. the best results have been obtained with cerium and lithium, which precipitate with chromates at ph values between 8. and 8.5
its in a really old book "How to make old-time photos" it states
sensitivity can be increased threefold by adding , to a bichromated colloid layer, a metal salt which precipitates on contact with a chromate but not with a bichromate. In this situation, the metal salt, itself, does not contribute to the tanning action. rather, it reacts with the neutral chromate which is formed during exposure and increases the tanning. the best results have been obtained with cerium and lithium, which precipitate with chromates at ph values between 8. and 8.5