Originally Posted by Tom Hoskinson
Jed's last response convinced me of the futility of further direct exchange with him on this subject. I am assuming a linguistic problem based on the fact that we speak different native languages. For the record, however, here is what I know about the use of pyrocatechin, both in solutions, and of its use as a developer. I think this information needs to be on the record because, frankly, there has been a lot of misinformation, and if I may dare use such lanaguage, flat-out BS, presented in this thread.
Let me remark that all of my testing has been carried out with fresh pyrocatechin, white or beige in color. The reducing potential of pyrocatechin decreases with age and one should not expect the same results when testing with old pyrocatechin.
1. Pyrocatechin is for all practical purposes extremely stable in propylene glycol solutions. I have pyrocatechin/glycol solutions on hand that are 2.5 years or older, and they still work just as they did when mixed.
2. A simple developer that contains nothing other than pyrocatechin, in the amount of about 1-2g per liter of working developer, and potassium carbonate, produces a lot of stain.
3. If one adds sulfite to the simple pyrocatechin developer the stain will decrease in intensity, and if enough sulfite is added this developer will eventually become a non-staining developer. Relatively little sulfite is needed to make the developer non-staining, since pyrocatechin is much more sensitive to sulfite than pyrogallol.
4. If one adds ascorbic acid to the simple pyrocatechin developer the stain will decrease in intensity, and if enough ascorbic acid is added this developer will eventually become a non-staining developer. Very little ascorbic is needed to make the developer non-staining.
5. If one adds a secondary reducer to the simple pyrocatechin developer, say metol, phenidone, or p-aminophenol, the stain will becom less intense. The more of the secondary developer one adds, the less will be the stain. If you add enough of the secondary reducer, the stain will disappear altogether.
As you know, several years ago I modified the Pyrocat-HD formula by increasing the amount of sulfite in it to make it non-staining. This topic was discussed widely on the AZO forum.
If anyone has actual data from testing to disprove any of my findings I welcome it. But until such time as such data is presented, my own empirical data supports all of the conclusions listed above.
Last edited by sanking; 02-13-2007 at 05:42 PM. Click to view previous post history.