Print bleach (split) strange behavior

[bernard_L]

I need to lift highlights on some prints to improve the highlight "snap". Ilford MG IV FB, Dektol 1+2 2Min, fix, wash 5min (will be re-fixed and re-washed later anyway...). [disclosure: also posted on PN; there may be some overlap, but definitely not identical audiences]

I used the split method, ferricyanide (0.2%=2g/l) first, later (re-)fix. And, yes, the ferricyanide crystals had a nice bright orange color. Keeping a reference print (actually a test strip) in sight. From available documentation I was expecting to see the effect of bleaching as silver was re-oxidized to halides(?), and that the subsequent fix would only remove the invisible but unwanted silver halides(?).

Instead I spent 5 minutes watching, with no visible change. I briefly rinsed the test strip, then back to fixer for ~1min, then (drip) back into ferricyanide. Then some bleaching occurred, fairly fast. So it seems (in that instance) that ferricyanide alone has no visible effect, and will be effective only mixed with fixer. Meaning the split (and reversible) method (re-develop the halides if you bleached too far) does not work for me. Can someone explain? I propose in exchange my gratitude.

 

[Bob Carnie]

Did you put the print into sulphide to *** develop the image*** or did you go from bleach to fix... If so all you will see is the bleaching effect of the ferri.

 

[bernard_L]

Did you put the print into sulphide to *** develop the image***

I don't think I mentioned sulphide. I am not toning. Just bleaching to lift the highlights. I did mention re-developing (in normal developer) as a possibility offered by the split method where the fixer is not mixed with the ferricyanide. But that was not part of the enumeration of steps describing my precise problem.

 

[Photo Engineer]

The Ferricyanide bath should have some Bromide in it such as NaBr or KBr.

 

[Bob Carnie]

Obviously I do not understand your question.

You should see an immediate lightening of tone with bleach alone. to the point of completely removing the image if left long enough and with a strong bleach.

If you are not seeing a bleaching effect then you should make bleach stronger.

I don't think I mentioned sulphide. I am not toning. Just bleaching to lift the highlights. I did mention re-developing (in normal developer) as a possibility offered by the split method where the fixer is not mixed with the ferricyanide. But that was not part of the enumeration of steps describing my precise problem.

 

[bernard_L]

Thanks a lot PE. Added 2g/l KBr, and it works as expected. Useful lifting of highlights in ~2min, just fast enough but not too much. Indeed I had some doubts as to how the re-halogenation might occur, putting in my original post question marks after each mention of halides. Don't remember where I saw the mention of split bleaching with ferricyanide (that is, not mixed with fixer), but I'm pretty sure they did not mention KBr.

 

[Olli J]

Reaction to ferricyanide reduction varies between paper brands. Ilford MG IV FB is one that reacts sluggishly and kind of unpredictably. Almost any other paper would be easier to reduce with ferricyanide.