[pure-silver] Re: Purple-Tinted Negs


----- Original Message ----- From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, May 31, 2006 3:00 PM
Subject: [pure-silver] Re: Purple-Tinted Negs


Maybe the techs at Kodak Professional are crazy but
they've told me several time that the "too long in the
fixing bath" issue we were all taught to fear, is a
myth insofar as film is concerned.  i.e. that the
shadow/midtone whatever info would be lost/dissolved
or whatever if fixed for too long.  They said they ran
tests and fixxing could be as long as 6 minutes in
Rapid Fix.

Given that, I standardized with 5 minutes for fixing
here, and; I NEVER fix more than 30 rolls per 1/2
gallon, I use HCA with agitation (Jobo) for 1-3
minutes. A minute is fine but longer won't hurt
anything, and I NEVER have purple negs whether it be
T-Max or otherwise.

Different films will have a different color.  PlusX
looks blue for example, and a stack of processed Tri-x
sheet film waiting to be sleeved has that purple
color, yet individually the sheets look perfect.
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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