Fogging Developer for Reversal

[grainyvision]

Yeah dithionite seems to have been retained mostly in laundry or dyeing products where the normal usage is one shot and you never prepare anything before using it. I think most powder products in photography require elevated temperature to mix and so we usually don’t do that. One shot stuff tends to be solvent based. I’ll try the dithionite thing some more and see if it’s worth it.

The only potential lead toward making a solvent based version of dithionite is dithionite dissolved in triethanolamine. There's a patent about dithionite being preserved in it. In actual usage it does work to some extent, but far from perfect. Fresh mixed when mixing the solvent with equal part water will make film darken to black almost instantly, but after 1 week in refrigerated storage (note my TEA is low freeze grade, so doesn't freeze at a temp of around 40F) it'll only turn a dark brown after a few seconds and takes a while to turn completely black. This might still be close enough for a fogging developer though if you account for the imprecision with additional time. After 1 month the solution was still active. It seemed like it decreased in activity a lot over 1 week, but afterwards the activity level seemed fairly stable for 1-2 months. I only tested this once though so take with a grain of salt. I can't find my notes for how much dithionite I actually dissolved

 

[relistan]

The only potential lead toward making a solvent based version of dithionite is dithionite dissolved in triethanolamine. There's a patent about dithionite being preserved in it. In actual usage it does work to some extent, but far from perfect. Fresh mixed when mixing the solvent with equal part water will make film darken to black almost instantly, but after 1 week in refrigerated storage (note my TEA is low freeze grade, so doesn't freeze at a temp of around 40F) it'll only turn a dark brown after a few seconds and takes a while to turn completely black. This might still be close enough for a fogging developer though if you account for the imprecision with additional time. After 1 month the solution was still active. It seemed like it decreased in activity a lot over 1 week, but afterwards the activity level seemed fairly stable for 1-2 months. I only tested this once though so take with a grain of salt. I can't find my notes for how much dithionite I actually dissolved

That's pretty interesting, though. I guess the TEA is a strong enough base to activate the dithionite on its own, without the use of carbonate?

 

[Rudeofus]

TEA does different things to different reducers. While people seem to be quite happy with the shelf life of PC-TEA, CD-4 dissolved in TEA turns dark rather quickly in my experience. If TEA finds a way to talk Dithionite out of a Sulfur Dioxide molecule, it will happily form TEA-SO2 adduct and shift the reaction balance as far to the right as possible.