"Special" Developers for High Iodine Emulsions

[wildbillbugman]

Hello PE and All,
I recall that, in discussing Ag emulsions with high levels of I, PE wrote that these emulsions require "Special Developers". PE- I wonder if you can describe such developers. I have been working with higher levels of AgI and find some advantages. But they are very slow.
I have been working on some "weird" stuff that I won't go into yet. But weird is my nature. If I am successful, I will let everyone know what I have been up to.
Bill

 

[Photo Engineer]

Bill, I was not involved in this project and know little about it. I'll see what I can dig up. The highest I worked with was about 10%. It had great edge effects but could be developed normally.

PE

 

[wildbillbugman]

Thanks PE! I was worried when I read that you were ill. I am glad that you are feeling better. I have some Ag/halid emulsions that WILL NOT react even to open sunlight when coated and dried on glass plates. However, after being brushed with homemade D19 and dried again, theye become good in-camera emulsions. But they are slower than I would like. I am wondering id the right developer will speed them up a bit.
Bill

 

[Photo Engineer]

Try adding a silver halide solvent.

PE

 

[wildbillbugman]

PE,
Thanks ! I donno why I did not think of that.

 

[wildbillbugman]

PE,
Do you have any suggestions as to a solvent. Perhaps just lowering the pH. will do. H2SO4?

 

[Photo Engineer]

Silver halide solvents include Hypo, Thiocyanate, Sodium Sulfite, and Sodium Chloride in decreasing order of activity. So, where 1 g/l of hypo will be a good solvent, you may need 100 g/l of sodium chloride.

PE

 

[wildbillbugman]

PE,
That makes perfect sense. As I said before, I can coat,dry and expose glass panels and they will not react until I brush on D19, which contains a big dose of sodium sulfite.
In fact, coating the dried plates with sodium sulfite solution, or sodium carbonate, activates them to exposure. Weird,huh?

 

[Athiril]

I thought hypo was less active in solvent ability than thiocyanate?

 

[Photo Engineer]

Dan, that is hard to answer. I give them a tie.

The reason for the difficulty is that SCN is a swelling agent and so how much of the speed of fixation is due to swell??

PE