[pure-silver] Re: Purple-Tinted Negs

I'll have to try that dichroic fog remover next time
some dagnab Ilford film comes thru here.  Seem to get
it to some degree no matter what developer I use.
I agree testing is a very good thing for reassurance
if nothing else.
Eric

> > --- Richard Knoppow <dickburk@xxxxxxxxxxxxx>
> wrote:
> 
>    Ammonium thiosulfate fixer (rapid fixer) can
> dissolve 
> metallic silver when acid and given long enough. The
> problem 
> is mainly for the very fine grains of print images
> but can 
> occur with film if enough time goes by.
>    Normal fixing times for some films in film
> strength rapid 
> fixer is on the order of 6 minutes so the above is
> not 
> surprizing. If the film is left in for longer,
> perhaps 15 
> minutes, there may be some bleaching.
>    When neutral or alkaline the bleaching effect
> does not 
> take place. Actually, Sodium thiosulfate fixer can
> also 
> cause bleaching but it takes forever.
>    An effective bleach for removing dichroic fog can
> be made 
> from film strength rapid fixer by adding 15 grams
> per liter 
> of Citric acid to it. The film must be watched
> carefully to 
> prevent bleaching of the image.
> 
>    Stacking negatives may show up some tint, perhaps
> in the 
> support. I use mostly T-Max, both 100 and 400
> speeds, Tri-X 
> 400 roll film, and Plus-X roll film. I do not get
> tinted 
> negatives with any of these. I do observe a purple
> tint in 
> the used KHCA after treatment of T-Max.
> 
>    One does not have to rely on such indirect and
> perhaps 
> unreliable methods such as a residual tint to
> indicate 
> complete fixing. The easiest method is to use the
> Sodium 
> sulfide test. It is easy to make up and will give a
> good 
> indication of any residual silver in the emulsion.
> Kodak 
> used to recommend KRST at 1:9 diultion as a low-odor
> 
> alternative to Sulfide. They no longer do. I think
> this is 
> because the test works only on well washed film or
> paper. 
> The diluted KRST has the advantage of not having the
> rotten 
> egg odor of sulfide and having longer shelf life.
>    Its easy enough to test for good fixing
> periodically, or 
> perhaps better, with every batch fixed. Use scraps
> of film 
> or paper to make the test.
> 
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx 
> 
>
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