From: Monnoyer Philippe (monnoyer@imec.be)
Date: 02/18/03-03:56:38 AM Z
Richard,
My previous mail was for Jack, sorry.
I never tried that kind of reversal procedure with sulfide. Are there advantages ?
At least you give me an idea: I need extreme density ranges for palladium, and the silver sulfide should be first a good UV blocker, which raises the contrast in UV, and secondly, it's more archival. (and sulfide costs nothing).
Could you comment on the other advantages of that method ?
Philippe
|-----Original Message-----
|From: Richard Knoppow [mailto:dickburk@ix.netcom.com]
|Sent: Tuesday, February 18, 2003 02:01
|To: alt-photo-process-l@skyway.usask.ca
|Subject: Re: Bleaches
|
|
|
|----- Original Message -----
|From: "Philippe Monnoyer" <philippe.monnoyer@skynet.be>
|To: <alt-photo-process-l@sask.usask.ca>
|Sent: Monday, February 17, 2003 3:36 PM
|Subject: Re: Bleaches
|
|
|> Hi Richard,
|>
|> Well, a rehalogenating bleach won't work at all for
|reversal. These bleaches
|> contain either bromides, chlorides or iodides.
|> In the reversal process, the purpose of the bleach is to
|remove the black
|> silver image WITHOUT replacing it by silver halides
|(rehalogenating bleach).
|> If you do so, you transform the image back to what it was
|before
|> developpment, namely silver halides. So, you end up with
|an homogeneous
|> film/paper, like unexposed. If afterwards you developp it,
|everything will
|> turn black.
|> An adapted single bleach would have removed the first
|silver image, leaving
|> nothing else in the film/paper. That way, the second
|developpment will make
|> all but the initial image turn black. That's the reversal
|process.
|>
|> I think copper sulfate with a touch of sulfuric acid, like
|for dichromate
|> bleach, or permangante bleach will work OK. Try different
|concentrations.
|> Rinse thouroughly to eliminate silver sulfate.
|>
|> And keep us aware of the result,
|>
|> Cheers,
|>
|> Philippe
|
| The above is true where a conventional reversal process
|is used. There the final image is silver. If a sulfiding
|solution is used things are a little different. The metallic
|silver negative image does not have to be removed to develop
|the silver sulfide. Afther this second development there
|film will contain a negative image of metallic silver and a
|positive image of silver sulfide. If the film is now treated
|with Farmer's reducer the metallic silver image will be
|removed leaving the silver sulfide postive image. Farmer's
|reducer, is of course, a mixture of a rehalogenating bleach
|and hypo. The bleaching and fixing processes can be
|separated as two steps or combined as in regular Farmer's or
|as done in color "blix". The Ferricyanide bleach in Farmer's
|will not affect the silver sulfide.
| There may be other problems with this procedure and, of
|course, a sepia image must be acceptable, but it does work.
| I believe Permanganate bleach will also remove the
|sulfide.
|
|---
|Richard Knoppow
|Los Angeles, CA, USA
|dickburk@ix.netcom.com
|
|
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