TEA vs METABORATE
Alan: Your statement that 99% TEA is difficult to obtain in the UK made me re-think the use of TEA. Another disadvantage of TEA is that because the pH-versus-temperature curve differs from metaborate, the developer can't use a fixed-factor of XTOL's times for temperatures above 20C. It would need its own time-temperature table. So I've decided to pursue the previous baseline dev based on sodium metaborate that I posted here: http://www.apug.org/forums/viewpost.php?p=1397796
The main purpose of TEA was to provide strong buffering in order to minimise the effect of inaccurate measurement of sulfite. A good solution is to measure sulfite by weight instead of volume. I mentioned earlier in this thread that electronic scales are cheap. One with .1g resolution is only US$10. That's the same cost as a packet of XTOL! At that price, there is no excuse for folks to not have a scale. Search for "scale .1g" or "scale .01g" in amazon.com.
I ran another strip on the metaborate-based baseline dev last evening, but adding propylene glycol as if it came from a concentrate (and boosting metaborate by .1g to adjust pH). The PG made the dev-time increase to 13.1 minutes (it was 12.25 without the PG), and the results look the same: a hair finer grain than XTOL. Here are scans from XTOL and this soup:
XTOL: 11-29-b8-XTOL.jpg, Test-soup: 11-00-b8.jpg
Rudi: The only question remaining is the rate of the Fenton reaction. One informal test I did a few weeks ago using the baseline dev above was: Develop a strip, let the soup sit for five hours, and dev a 2nd strip with the same soup. I got a 5% density-loss (on a log scale), whereas I expected about a 1% loss from using the dev twice. That 1% loss per hour is fine for a one-shot dev that is specified to be used within 30-45 minutes after mixing. But I need to test to see if much faster loss can occur. And as you point out, the AA-density curve is nearly flat there, so an X % density-loss means there was a much greater ascorbate-loss. So tests should be run in a steeper part of the curve. An AA/Phenidone ratio of 20 (instead of my 90) would be appropriate. The PC-Sulfite developer that I posted in January would work well for this testing.
Jerry: Thanks for the info about ferric and ferrous ammonium sulfate. I'll put them to use.
After all these months, I'm trying to finish this project. I've settled on that baseline developer. Now I need to insure that Fenton-destruction isn't a problem, and then run some tests on various kinds of film.