I hope that potassium cyanide is NOT in your Farmer's reducer.
please enlighten me!!
i am a chemistry novice.
Potassium Cyanide, AKA Farmers reducer
Is using bleach more effective than using BTZ for fogged paper?
I have read the above several times and I am still unclear what the benefits are of a rehalogenating bleach over just potassium ferricyanide and then fixerYou mean potassium ferricyanide. Potassium cyanide is still sometimes used for fixing wet plate/collodion photographs, but my personal view is that it has no place in a modern darkroom whatsoever. A slight misstep with that stuff is lethal.
Farmer's reducer is a mixture of potassium ferricyanide and fixer, i.e. sodium or ammonium thiosulfate. Potassium ferricyanide by itself is just the bleach. When working on prints (or indeed, negatives), I prefer to mix potassium ferricyanide with potassium bromide to make a bleach that turns the silver image back into silver bromide (i.e. it's a rehalogenating bleach - it turns the silver back into a silver halogen). This leaves the image in a white/yellowish state which is invisible on paper, but on film it's actually visible. More importantly, if you bleach too far, you can retrieve the image by simply re-developing it in any B&W developer. If the bleaching action is to your liking, you can then proceed to fix the paper/film to make the bleaching permanent; this will remove the bleached out silver bromide part of the image definitively. This approach gives you more control, since you can go back and correct mistakes.
Not necessarily, but bleaching has the benefit that you can do it after the print is done and you're still not happy with it. It also has the benefit that you can apply it in specific places with a brush, cotton pad etc. So overall it gives you more control.
the benefits are of a rehalogenating bleach
just potassium ferricyanide and then fixer
Melvin, as mentioned it's potassium ferricyanide you're after. Bruce Barnbaum has a very detailed and easy to follow explanation in his book "The Art of Photography." I rarely use a complete bath,but often use selective bleaching. I had the opportunity to do a darkroom session with the great cowboy photographer Jay Dusard in Jackson Hole. Jay's nickname is Captain Ferricyanide..... & his prints are beautiful.
It has been my experience that assessing the degree of bleaching before fixing can be misleading as the act of fixing can increase the effect of bleaching.
never used rehalogenating bleach, just ferricyanide (with a brush and fix with another brush, little by little, until eventually the effect is too much and i have to throw the print away).I prefer to mix potassium ferricyanide with potassium bromide to make a bleach that turns the silver image back into silver bromide (i.e. it's a rehalogenating bleach - it turns the silver back into a silver halogen). This leaves the image in a white/yellowish state which is invisible on paper, but on film it's actually visible.
It's not very critical; a dash of this and a teaspoon of that. I never bother to measure. If the action is too slow, add ferricyanide and/or bromide. If the bleach starts fast enough but slows down with use, you can regenerate it by adding some bromide and ferricyanide. I always do this the seat-of-the-pants, intuitive way.what are the proportions of ferricyanide and bromide for this bath?
Yes, you could use the SLIMT concentrates and combine them for this purpose.i have used slimt technique with negatives, that uses a bleach with these components: are those proportions useful also for prints?
It's not very critical; a dash of this and a teaspoon of that. I never bother to measure. If the action is too slow, add ferricyanide and/or bromide. If the bleach starts fast enough but slows down with use, you can regenerate it by adding some bromide and ferricyanide. I always do this the seat-of-the-pants, intuitive way.
Yes, you could use the SLIMT concentrates and combine them for this purpose.
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