B&W Paper Reversal New Method?

[hvfrancesco]

For bw paper reversal I'm still experimenting with a re-halogenating bath of sodium periodate and sodium chloride.
I found rather difficult to buy strong oxidizers in my country, so I couldn't follow the peroxide path, but I had easy access to a solution of sodium periodate because it is normally used in screenprinting to reclaim screens removing old photo-emulsion.
with this method the negative silver image is turned mainly into silver chloride that is soluble in a bath of diluted ammonia (I've been using a 1.5% solution) while silver bromide is not.
The results are good, the chemicals involved rather safe (ammonia is nasty but it is used at a rather low dilution ratio) and the process is quicker than the peroxide one, withouth the potentially emulsion-damaging bubbling.
I've been experimenting with a sodium periodate only bleaching bath, where periodate acts as both bleach and re-halogenating agent. In this case you can avoid the ammonia bath as silver in neg image is turned into silver iodide, leveraging the fact that silver iodide is less sensitive to developing, this process is even faster and cleaner but more difficult to control as sometines part of the negative image appears anyway, producing muddy highlights or some sort of solarization. Another disadvantage of periodate only method Is the fact that you are left with plenty of silver iodide to get rid of in fixing bath, possibly leading to a rapid exhaustion of fixer.

I attach two images, the first one is a direct positive on Forma paper processed with periodate+sodium chloride and ammonia, the other with a periodate only bleach bath

[Raghu Kuvempunagar]

For bw paper reversal I'm still experimenting with a re-halogenating bath of sodium periodate and sodium chloride.
I found rather difficult to buy strong oxidizers in my country, so I couldn't follow the peroxide path, but I had easy access to a solution of sodium periodate because it is normally used in screenprinting to reclaim screens removing old photo-emulsion.
with this method the negative silver image is turned mainly into silver chloride that is soluble in a bath of diluted ammonia (I've been using a 1.5% solution) while silver bromide is not.
The results are good, the chemicals involved rather safe (ammonia is nasty but it is used at a rather low dilution ratio) and the process is quicker than the peroxide one, withouth the potentially emulsion-damaging bubbling.
I've been experimenting with a sodium periodate only bleaching bath, where periodate acts as both bleach and re-halogenating agent. In this case you can avoid the ammonia bath as silver in neg image is turned into silver iodide, leveraging the fact that silver iodide is less sensitive to developing, this process is even faster and cleaner but more difficult to control as sometines part of the negative image appears anyway, producing muddy highlights or some sort of solarization. Another disadvantage of periodate only method Is the fact that you are left with plenty of silver iodide to get rid of in fixing bath, possibly leading to a rapid exhaustion of fixer.

I attach two images, the first one is a direct positive on Forma paper processed with periodate+sodium chloride and ammonia, the other with a periodate only bleach bath

Interesting approach! Did you notice any loss density when using periodate+chloride bleach on paper? As paper has chloride in it, wouldn't Ammonia eat up some of it and lead to loss of density?

[hvfrancesco]

Interesting approach! Did you notice any loss density when using periodate+chloride bleach on paper? As paper has chloride in it, wouldn't Ammonia eat up some of it and lead to loss of density?

yes, the chloride in the unexposed parts of the paper may be affected too, but in my tests up to now it doesn't seem to affect too much the overall density. I suppose it depends much on the kind of paper used and its original bromide-chloride ratio.