Basic Question About Potassium Bromide

[joko]

I've never made an emulsion, but I've been looking over the recipes and reading the threads here, and I've come up with a question.

In developing, Potassium Bromide acts as a restrainer in paper developers.

It's in a lot of emulsion formulas. Why? Is it acting as a restrainer in emulsions, too? I'm looking for an elementary answer.

Potassium Bromide and Potassium Iodide seem to be in several of the formulae for emulsions, like the "Real Emulsion" thread, above. Can you just leave out or reduce the Potassium Bromide and pick up speed? I suspect that it's in there to help fuel a reaction or create something else. Is the proportion of Potassium Bromide to Potassium Iodide somehow important? Are they working together, like in the "Real Emulsion" formula? Thanks. J.

 

[Ian Grant]

No it's forming Silver bromide which is photo-receptive, and will reduce to silver with light & developer.

It is the key compound along with Silver Nitrate and cannot be left out !

That's the SIMPLE answer, now watch for the complex ones

Ian

 

[Kirk Keyes]

Ian's right. Also, having a small excess of bromide can also help stabilize the silver halide in the finished emulsion and help prevent fogging.