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Photo Forum / Film Photography / Darkroom / March 2004repairing negative with dichroic fog?
I have several Plus-X negatives that have a mottled base fog with transmitted light and a metallic sheen with reflected. I think this is dichroic fog; it took me around six months to identify this problem, so the negatives have been sitting in their negative sheets for quite some time. I've tried refixing in TF-4 for about 10 minutes, but this seems to do nothing. Is there anything else I can do? I like the images, but the prints look fairly awful because of the fog problem. Thanks in advance! Often refixing the film in fresh Kodak Rapid Fixer will remove dichroic fog. The fresh fixer has a slight bleaching property which will remove the small amount of silver on the surface of the film. Normal fix times of 3-5 minutes shouod be enough. Good luck. Bernie > Often refixing the film in fresh Kodak Rapid Fixer will remove dichroic fog. > The fresh fixer has a slight bleaching property which will remove the small > amount of silver on the surface of the film. Normal fix times of 3-5 minutes > shouod be enough. Good luck. He said in his post that he refixed the negatives. But using TF-4, which is an alkaline fixer. Would that make a difference? > > Often refixing the film in fresh Kodak Rapid Fixer will remove dichroic fog. > > The fresh fixer has a slight bleaching property which will remove the small > > amount of silver on the surface of the film. Normal fix times of 3-5 minutes > > shouod be enough. Good luck. > > He said in his post that he refixed the negatives. >>He said in his post that he refixed the negatives.<< Yes, but with home mixed alkaline formula fixer. You need the activity of the ammonium hypo in a fresh unused fixeer to provide the sllight bleaching effect which removes the dichroic fog, if this is dichroic fog. Usually dichroic fog is even, not mottled, but I have seen many stange things happen in the darkroom and generally try to test for the obvious first. Bernie > >>He said in his post that he refixed the negatives.<< > > Yes, but with home mixed alkaline formula fixer. You need the activity of the > ammonium hypo in a fresh unused fixeer to provide the sllight bleaching effect > which removes the dichroic fog, if this is dichroic fog. I stand corrected. Good information. Thank you, Bernie. > > >>He said in his post that he refixed the negatives.<< > > [quoted text clipped - 3 lines] > > I stand corrected. Good information. Thank you, Bernie. Alkaline or neutral fixer will not work, it must be acidified. A good bleach is made from fresh film strength acid rapid fixer with Citric Acid added to 15 grams/liter of working strength fixer. This will remove dichroic fog with little, if any, effect on the image. The old standard method was to use about a 1% solution of Potassium Cyanide, which is a very effective silver solvent. Cyanides are probably not good things to have around your house so the modified fixer remains the best choice.  Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com Richard Knoppow wrote (in part): > The old standard method was to use about a 1% solution of Potassium > Cyanide, which is a very effective silver solvent. Cyanides are > probably not good things to have around your house so the modified > fixer remains the best choice. What's the matter, Richard? No sense of adventure? Was there not some iodine in that, too? Signature.~. Jean-David Beyer Registered Linux User 85642. /V\ Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 08:40:00 up 6 days, 10:50, 2 users, load average: 4.24, 4.19, 4.12 > Richard Knoppow wrote (in part): > > The old standard method was to use about a 1% solution of Potassium [quoted text clipped - 5 lines] > > Was there not some iodine in that, too? Not for clearing dichroic fog. Iodine is used in a reducer for clearing lots of silver. It converts the silver to silver iodide. Because silver iodide is resistant to sodium thiosulfate fixer a mild solution of cyanide is used to remove it. A more modern version uses ammonium thiosulfate fixer, which has an easier time with silver iodide. Dichroic fog is composed of colloidal silver deposited on the surfaces of the film. Cyanide is a good enough solvent for metallic silver to remove it. However, Ammonium thiosulfate fixer acidified with Citric Acid is effective enough, easier to control, and much safer than cyanide. Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > I have several Plus-X negatives that have a mottled base fog with > transmitted light and a metallic sheen with reflected. I think this is [quoted text clipped - 5 lines] > > Thanks in advance! A mild siver solvent can be made from fresh rapid fixer at film strength with 15 grams/liter of Citric Acid added. The film should be treated in this solution and inspected continuously. You can re-treat it if there is still some dichroic fog left but too long a treatment will begin to dissolve the image silver. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com |
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