Propylene glycol (PG) reduces developer-activity.

I was wondering why my concentrated developers were consistently less active than the identically-formulated ones directly mixed into water (without the PG carrier). Was I damaging the developers by heating the PG solution to 50C or with the extra handling? So I formulated one in water, developed a test-strip, then added 3.7% PG (by volume) and dev'd another strip. Significantly thinner, more than the extra 3.7% dilution could cause.

Here's the 1-liter version of the developer I tested. Its image-quality is virtually identical to XTOL, with the same dev-times. I added ingredients in this order:

Ascorbic acid ..................... 10.7 g
Sodium metaborate ............. 7.5 g
Sodium sulfite .................... 90 g
Phenidone .......................... 0.15 g (use a 1% solution with PG)

I'm hoping I can get the non-sulfite portion of this into a PG-concentrate suitable for 1+19 dilution.

If you add boric acid and boost the alkali a little to get the same pH, the resulting developer is a little less active. Any idea why? Does the resulting buffer-system hinder activity somehow?

Mark Overton