Quote Originally Posted by pdeeh View Post
What surprised me about the instructions for Pyrocat-HD in glycol (as per http://www.pyrocat-hd.com/html/mixing.html) is the suggestion that the KBr and metabisulfite is introduced into the glycol as a solution in water - I'd have assumed that this would defeat the object of using glycol, which is to keep water out of the stock solution, isn't it?

Perhaps Ian or Gerald or similarly chymical gentleman could fill me in on why it seems to be OK in this case?
They won't dissolve in Glycol so must be dissolved in water, a little water won't affect the keeping properties. It's important to use fresh Metabisulphite as it's the SO2 it releases that stops oxidation of the Pyrocatechin. Once the Metabisulphite breaks down the developer collapses.

Oxygen is absorbed into water but not into Glycol which helps prevent oxidation. In practice with fresh Metabisulphite and the right bottles I have Pyrocat HD without Glycol that's lasted from March 2011 and is still OK today, so over 2 years.

Commercial developers made up in Glycol or similar need some water to dissolve some of the components.