This may be related to the other 'black silt' thread on this forum, maybe not. It is not a question about the efficacy of adding rapid selenium to film fixer for archival purposes, it's a question about why the black silt is appearing.
In the past, I've added Kodak rapid selenium to my fixer with no untoward results. These were typical non-hardening, acid fixers. To simplify my processing I've recently switched to Formulary T-4, a positive ph fixer, (no stop bath, just a rinse between steps). Now, however, I get a black percipitate in the stored fixer, although, initially, it still seems to clear the film ok.
I assume that adding the selenium to a positive ph fixer is a no-no and that this is the cause of the percipitate (which I also assume is the silver that accumulates in partially used fixer). While I intend to drop this practice, I'd appreciate comments from anyone who can shed light on what's happening. Also, is it possible that Jerry's students are introducing toner into the fixer they're using?
In article <29835016-fe0c-468f-b80d-77b49411c...@t32g2000yqj.googlegroups.com>,
Lew <lew1...@gmail.com> wrote: >This may be related to the other 'black silt' thread on this forum, >maybe not. It is not a question about the efficacy of adding rapid >selenium to film fixer for archival purposes, it's a question about >why the black silt is appearing.
>In the past, I've added Kodak rapid selenium to my fixer with no >untoward results. These were typical non-hardening, acid fixers. To >simplify my processing I've recently switched to Formulary T-4, a >positive ph fixer, (no stop bath, just a rinse between steps).
I am very skeptical about this stuff. The rationale for its wash-time claims is wrong, and I've seen it cause serious problems with selenium toner in the past.
-- Thor Lancelot Simon t...@rek.tjls.com "Even experienced UNIX users occasionally enter rm *.* at the UNIX prompt only to realize too late that they have removed the wrong segment of the directory structure." - Microsoft WSS whitepaper
> This may be related to the other 'black silt' thread on > this forum, > maybe not. It is not a question about the efficacy of > adding rapid > selenium to film fixer for archival purposes, it's a > question about > why the black silt is appearing.
> In the past, I've added Kodak rapid selenium to my fixer > with no > untoward results. These were typical non-hardening, acid > fixers. To > simplify my processing I've recently switched to Formulary > T-4, a > positive ph fixer, (no stop bath, just a rinse between > steps). Now, > however, I get a black percipitate in the stored fixer, > although, > initially, it still seems to clear the film ok.
> I assume that adding the selenium to a positive ph fixer > is a no-no > and that this is the cause of the percipitate (which I > also assume is > the silver that accumulates in partially used fixer). > While I intend > to drop this practice, I'd appreciate comments from anyone > who can > shed light on what's happening. Also, is it possible that > Jerry's > students are introducing toner into the fixer they're > using?
Where did you get the idea of adding the toner to the fixer? While KRST does contain a considerable amount of ammonium thiosulfate it should not be added to a fixing bath, particularly an adid one. The acid will decompose the toner causing the selenium to be precipitated. Prints which are too acid may develop a peach colored stain in the toner. In the past Kodak recommended mixing KRST with Kodak Hypo Clearing Agent at 1 part toner to 19 parts diluted wash aid as a combination method of decreasing wash time and protecting the image. It was discovered nearly twenty years ago that this method failed on microfilm because the low density areas of the film were not toned enough to protect them from oxidation. The method was never recommended for stronger dilutions of KRST. KRST will provide full image protection but must be used at a dilution of no greater than 1:9 and for about a minimum of three minutes. With most paper this will cause a change in image color or density. Prints to be toned should be treated in a sulfite wash aid such as KHCA and washed. Then toned and washed again. Since there is no acid in the toner the use of a wash aid treatment after toning is probably not necessary. I am also skeptacle of the use of alkaline fixing baths. Since sulfite wash aid gives even shorter wash times and does not have the disadvantage of allowing carried over developer to continue working in the fixing bath. The current recommendation for _image protection_ is to use a polysulfide toner, like Kodak Brown Toner, for just enough time to cause a slight change in image color (some papers will not show this). KBT and similar toners tone all densities at the same rate so relatively slight tonign will give some protection. However, the criteria for microfilm is to obtain a minimum of 60 percent toning as determined by bleaching the silver image and measuring the density of the toned image. This is based on work done by the Image Permanence Institute of the Rochester Institute of Technology and at least some of it is available on the web. Very good image permanence can be gotten with quite conventional processing. Mostly one should be careful that the fixer is fresh (use a two bath fixing method) and that washing is thorough (although you _can_ wash too much). The use of a toner will help prevent oxidation of the image silver. _Complete_ toning in any sulfiding toner, selenium toner, or in a gold toner will provide very good image protection. Where the color change is acceptable (or desired) complete toning provides the best image protection.
-- Richard Knoppow Los Angeles, CA, USA dickb...@ix.netcom.com
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