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dannybee wrote:ok here it is my modifications
ferric sulphate 1g
potassium persulfate 1g
citric acid 50g I substituted it with acetic acid
lithium bromide 10g

a very slow working bleach test is drying but can tell from the test the refraction is much better and cleaner... I can tell this by viewing it as a transmission

OK. I assume if you replaced the 10g lithium bromide with roughly 7g potassium bromide you'd get about the same effect.

Keep in mind that lower bromide content of your rehalogenation bleach results in smaller grains and hence, less noise. However, this comes at the price of reduced diffraction efficiency.

ok here it is my modifications
ferric sulphate 1g
potassium persulfate 1g
citric acid 50g I substituted it with acetic acid
lithium bromide 10g

a very slow working bleach test is drying but can tell from the test the refraction is much better and cleaner... I can tell this by viewing it as a transmission

Without having tried myself, I'd expect that changing from potassium bromide to lithium bromide (or say, sodium bromide) will have little effect on the bleach.

What might be interesting with lithium bromide though, is that one could make bleach solutions at lower water concentration. Lithium bromide is highly soluble in alcohol. So one could design bleaches that swell the gelatin layer to a far lesser degree. E.g. ferric nitrate, ferric chloride, both well soluble in alcohol as well, come to my mind. I don't know if it would even be possible to have a bleach in absence of any water. From Jeff Blyth I learned that methanol does penetrate gelatin pretty fast. So it might be interesting to test a "dry" bleach in the context of some special techniques (SHSG etc.).

Well, Martin is probably the best person to answer this.

But, taking a bit of a speculative stab at it, Li is further up the periodic table than K. The purpose of the Br ion is to re-halogenate the silver speck. Since Li is further up the table, I would assume that it has a lower disassociatian energy and so forms ions morer readily. Thus, LiBr would produce more Br(-) ions, and so the probablity of capture by a silver speck is increased. Based on this argument, I would assume that LiBr is a better rehalogenating agent. But, it's probably also more reactive and I assume that if you have too many Br ions, then the chances of releasing HBr also increases, and that's probably not a good thing.

Martin?

very interesting modified PBU bleach for lower scattering..in the presentation "making analogue color holograms" . they lowered the Potassium bromide, I wonder if replacing the bromide with lithium bromide would do even better