Quote Originally Posted by Ryuji View Post
This formula is not robust against the errors made in the quantity of ascorbic acid. If you don't accept my knowledge on this topic, you should at least run somewhat decent sensitometric test, and report pH of each solution with varying amounts of ascorbic acid used.
Yes. Changing the ascorbic acid will change pH. Yet I just re-examined my negatives developed with 3.5g and 2.8g of AA. Their densities are practically identical. But 3.5 vs 2.8 would be a 25% measurement-error. With the virtually the same results. That's robustness.

Here are the pH's I measured:
3.5 g of AA: pH 8.21
2.8 g of AA: pH 8.33
XTOL: 8.37
Notice that XTOL is well above 8.20. I thought my meter was reading high, but I did a two-point calibration, and it passes the Borax-test. Methinks that Kodak boosted the pH a little after filing the patent.

Ryuji, when testing DS-10, you noticed that some 100-speed films develop poorly below pH 8.2. I suspect that Kodak observed the same thing late in the game, and boosted pH to give themselves more pH-headroom. Either that or my meter's defective.

Mark Overton