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View Full Version : SRAD's and KI questions



JOSarff
12-22-2008, 04:51 PM
I read in Photographic Emulsions by Wall that the addition of KI as a final reduces the emulsion speed. Is this because AgI has a lower sensitivity than AgBr or AgCl, or did I miss something?

Secondly, in SRAD emulsions can Ammonium Hydroxide be substituted for ammonia?

Photo Engineer
12-22-2008, 05:42 PM
Ammonium Hydroxide 28% is normally known as Ammonia solution, Household Ammonia is 2.8% and often contains a scent. It too is often called Ammonia in hardware and grocery stores. Ammonia itself is a gas. It is commonly used as a gas in refrigeration systems, but this stopped at the household level about 80 years ago as it caused many deaths due to leaks in home refrigerators. Ammonia gas can be easily liquified at ordinary pressures. I have done it on a lab scale with dry ice. I don't recommend it. Use the 28% Ammonia available for example from the Formulary an APUG sponsor.

KI does not reduce sensitivity, but rather increases it. Wall is incorrect on that as he is on many matters. It increases speed by broadening the spectral distribution of the emulsion as shown in Mees and James. However, since KI is an inhibitor it can be shown that massive amounts of KI can reduce emulsion speed by inhibiting development. OTOH, I have seen high speed pure AgI emulsions that were forced to develop in special developers that are very sharp and have normal speed, just poor development.

Wall probably poured in a huge dose of KI and then found that he got low speed, assumed KI reduced speed, but what it really did was reduce development rate at the huge amount Wall used. Use between 0.1% and 3% based on Silver moles and you will be in a safe range.

PE