Quote Originally Posted by albada View Post
So adding PG to water slows development, but when the PG is in a concentrate, it accelerates development. Weird, isn't it?
This is a wild guess but maybe it inspires more educated guesses: I have read it many times that PG forms an ester with the borate ion, and my little high school chemistry knowledge tells me that esters are more likely to form when water is forcibly removed. If all this is correct, I would assume that PG-Borate ester is formed in the concentrate version, which may have different properties from Borate and PG alone. It would be interesting to know whether different pH adjustments are needed with concentrate or fresh mix.

Since Mark observed that a given amount of PG has much more pronounced effect on small test clips than on whole rolls of film, it looks like PG somehow interacts with the gelatin or some other part of the emulsion.

PS: About the 1+1 dilution: I did an 120 roll in 500ml of developer, which means my results may or may not apply to 35mm rolls souped in 250ml.