Been working on this for a little while.
Dichromate bleach is excellent and reliable. Of course people have concerns with it.
Permanganate bleach is unreliable and damages film, but is much safer for you to handle. And as it reduces, MnO2 precipitates onto the surface of the film, and also inside of the gelatin. Emulsion can peel off as well.
Anyway, one example, which worked well for me, ended up with a dMax of 2.12 of unexposed area (old base fogged film, so it's pretty good), was potassium permanganate (enough to get that 'opaque' look in solution) in 250g/L of citric acid.
Silver Citrate isn't soluble in water, but it is in a good concentration of citric acid. Citric acid also keeps MnO2 from building up on or in the film. And it takes the edge of the permanganate bleach, so that it can be run at elevated temperatures and long times without damage.
It is however one shot, as the citric acid slowly reduces the permanganate and eventually clears it completely.
The time it took me to bleach a film with this was approx 16 minutes or so. I added some more potassium permanganate solution to it near the end (just a little) to finish it off.
The other thing I have done is copper sulphate with sodium chloride. Followed by a 300g/L Ammonium Chloride bath to dissolve the silver chloride selectively. Bleaching was done quickly, but the clearing time in the ammonium chloride I used was 30 minutes, but it becomes hard to tell when to finish. Think I also had the absolute thinnest neg left over stacked on top of the positive, basically unnoticeable.
But some of the silver bromide was also dissolved. dMax on the same film and developer process with this ended up being just 1.52 down from 2.12, but otherwise did work.
Dichromate bleach is excellent and reliable. Of course people have concerns with it.
Permanganate bleach is unreliable and damages film, but is much safer for you to handle. And as it reduces, MnO2 precipitates onto the surface of the film, and also inside of the gelatin. Emulsion can peel off as well.
Anyway, one example, which worked well for me, ended up with a dMax of 2.12 of unexposed area (old base fogged film, so it's pretty good), was potassium permanganate (enough to get that 'opaque' look in solution) in 250g/L of citric acid.
Silver Citrate isn't soluble in water, but it is in a good concentration of citric acid. Citric acid also keeps MnO2 from building up on or in the film. And it takes the edge of the permanganate bleach, so that it can be run at elevated temperatures and long times without damage.
It is however one shot, as the citric acid slowly reduces the permanganate and eventually clears it completely.
The time it took me to bleach a film with this was approx 16 minutes or so. I added some more potassium permanganate solution to it near the end (just a little) to finish it off.
The other thing I have done is copper sulphate with sodium chloride. Followed by a 300g/L Ammonium Chloride bath to dissolve the silver chloride selectively. Bleaching was done quickly, but the clearing time in the ammonium chloride I used was 30 minutes, but it becomes hard to tell when to finish. Think I also had the absolute thinnest neg left over stacked on top of the positive, basically unnoticeable.
But some of the silver bromide was also dissolved. dMax on the same film and developer process with this ended up being just 1.52 down from 2.12, but otherwise did work.
