As Bill Troop says in A&T, the fixer is derived from the fact in Haist that an alkaline fix swells the paper to its maximum allowing rapid diffusion of chemicals in and out of the paper, and also allows rapid washing for the same reason.
The swell, introduced by the alkalinity, is the key here.
"As Bill Troop says in A&T, ..."
And the greater the alkalinity the better; up to " 10.5 ".
From rec.photo.darkroom. There in years gone by Bill has
gone to great lengths discussing the alkaline fix.
"...rapid washing for the same reason."
"The swell, introduced by the alkalinity,
is the key here."
The emulsion becomes more fluid, watery.
Absorbtion and Desorbtion also play a part.
How about an alkaline wash, running or still
water? The later I do, few but long soaks.
After all isn't archival also alkaline? Dan
Bill got the information in interviews with Haist and from his book. He fully cites his references with credit to Haist. The pH 10.5 fixes were known for years and used by Kodak in the P-122 and Xomat processes.
The emulsion swells, but does not become more fluid, just as a sponge does not become more fluid as it swells. It merely contains more water and this can be measured using a swellometer. As far as stability goes, no, archival is not alkaline. The atmosphere is mildly acidic and oxidizing and the wash water is nearly neutral so the final pH after wash will be close to neutral and swell will have decreased thereby. As it dries, swell goes back to nearly the same value as before processing.
I just like that there's something called a "swellometer." Do you have a picture of one?
Originally Posted by David A. Goldfarb
Kodak built their own and they don't match anything commercially available.
Basically, there was a 1" square well with a dam around it. A lever with a circular plate was lowered gently onto the photo material being tested, and thickness was measured.
Then the head was raised just a mm or so, and the well was infused with the solution being tested. The plate was dropped immediately and a timer was started as well as a strip chart recorder. This measured initial thickness and then thickness as a function of time. The test was continued until the swell had stabilzed.
The dam could be raised to dump the solution and the next processing step could then be carried out.
The attached is a commercial swell test posted on the internet. It tracks the gain in weight vs pH using bone gelatin. If you flip the graph on the horizontal axis (but not the pH scale), you get an approximate plot of the swell behavior of pig gelatin vs pH. If you read the scale from right to left, you see an approximate plot of swell for B&W materials during processing, and if you imagine a roughly straight line, you have a B&W material developed, rinsed and then fixed in TF-4. The swell pretty much stays at its maximum level.
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Thanks, that's interesting.
Very interesting - thank you.
Wow a scientific swellometer - I figured that would be the number of good comments on a posted images indicating how swell it is, or after a big meal that top trouser button that just has to be undone as I swell.
My photos are always without all that distracting color ...
I stopped using a stop bath when developing B&W film a few years ago. Given the cost of film (5x4 and 10x8) and the even higher 'cost' of the time to shoot I decided to stop trying to save a few pennies by reusing chemicals and dump them after processing. I find 500ml of dev and fixer for 10 sheets of 5x4 or 5 of 10x8 in an expert drum gives me consitant results with one less step to cock up. I do still wash between the steps when processing E6 though.
If a practitioner regularly processes film using a water stop bath (no acid stop bath, just three water changes), what harm, if any, would result from moving the film directly from the developer to the first of the fixing baths???