Pyro times & fixing

[David A. Goldfarb]

You're probably seeing a combination of carryover and reduction of stain.

Disparagements regarding the current faddishness of alkaline fixers notwithstanding, I would just note that if you switch to an alkaline fixer, you won't need to worry about overfixing or reduction of stain in the fixer.

 

[Jorge]

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (David A. Goldfarb @ Oct 19 2002, 07:13 AM)</td></tr><tr><td id='QUOTE'>You're probably seeing a combination of carryover and reduction of stain.

Disparagements regarding the current faddishness of alkaline fixers notwithstanding, I would just note that if you switch to an alkaline fixer, you won't need to worry about overfixing or reduction of stain in the fixer.</td></tr></table><span id='postcolor'>
Why? I understand the alkalinity will prevent reduction of stain. But the overfixing I dont understand why not. What are the components of alkaline fixers? If I recall my chemistry correctly it is necessary to form sodium argentothiosulfates for easy removal. Hypo made of sodium thiosulfate made this possible, many people added ammonium chloride to speed the reaction and then the switch was made to ammonium thiosulfate for "rapid fixers". I suspect alkaline fixers are made of alkaly thiocyanates but in the end double silver salts have to be formed for removal thus the possibility of overfixing.

 

[David A. Goldfarb]

Jorge, you may have a point. It is claimed that alkaline fixers reduce the problem of overfixing, and if I understand correctly, this is because they do not reduce the stain, which is part of the image, and they do not dissolve image silver (i.e, alkaline fixers should only dissolve undeveloped silver) in the way that acid fixers can with excessive fixing times. Is this claim true?--I'm not sure, but I think this is the basis of the claim.

 

[Jorge]

jdef, yes, I beleive there is still risk of over fixing. 4 to 5 minutes is not excessive even in an acidic fixer so you are safe.

David, Ah I see.....you know if the stain is proportional then I would be afraid of dissolving silver in the shadow zones. I am still not clear why an alkaline fixer would not dissolve image silver. I wish someone could give us the formula and an explanation. As a matter of fact, if you have a bottle David why dont you check out the ingredients, I beleive they have to list them even if they dont put the ratios.

 

[David A. Goldfarb]

TF-4 doesn't list the ingredients. It is ammonium thiosulfate based, according to Photographers' Formulary (I asked), but I don't know what the other ingredients are. Aren't they required to provide a data sheet for safety reasons? I think there is some way of getting that information.

 

[Jorge]

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (David A. Goldfarb @ Oct 19 2002, 10:12 PM)</td></tr><tr><td id='QUOTE'>TF-4 doesn't list the ingredients. It is ammonium thiosulfate based, according to Photographers' Formulary (I asked), but I don't know what the other ingredients are. Aren't they required to provide a data sheet for safety reasons? I think there is some way of getting that information.</td></tr></table><span id='postcolor'>
Yeah! I thought they were supposed to provide a safety data sheet if one requests it. But I can tell you if it is ammonium thiosulfate there is a risk of overfixing I dont care what they say. I think I will drop them a line and ask for the safety data sheet. Thanks David.

 

[David A. Goldfarb]

Congrats on your negs, and please call me David.

Just FYI www.fineartphotosupply.com offers an alkaline fixer as well, which the manufacturer assures me is very similar to TF-4. I use TF-4, because I can buy it off the shelf at B&H and save the shipping cost (the fixer itself is about the same price either way), but if you're having it shipped anyway, it's another option.

I asked Anthony Guidice at Fine Art Photo Supply about selling it as a powder to avoid the cost of shipping water, but he said he felt that would be less convenient for users, due to the problem of precipitates developing from water impurities or not mixing the chemicals in the correct order. It seems these "problems" have obvious solutions--use distilled water and read the darn directions, so I suppose there may be an alternate reason, like it would be too easy to hack the formula if they sold it in powdered form, or maybe they use a subcontractor to make the chemicals, and it's just easier to do this way for some manufacturing reason.

 

[Jorge]

Ok, I just corresponded with Anthony Gudice from FAPS and he confirmed my suspicions, alkaline fixers are made of ammonium thiosulfate and they will overfix material. Apparently some of the associated reactions are dimished in the presence of alkaline medium but the potential to over fix is still there. So dont go grab a beer while you are fixing....