Hello Klaus,
Both substances are highly prone to oxidation, which limits their shelf life and promotes the formation of a (stain) fog.
I have experimented quite a bit with both, but have come to the conclusion that the existing formulations – namely PMK with pyrogallol and Pyrocat-MC with brenzcatechin – are virtually impossible to improve upon and, above all, deliver perfectly adequate consistency (variation <0.1D) and minimal fog. For my part, I have only changed the way I store my stock solutions; I therefore make use of the privileges of a raw chemistry enthusiast and prepare the stock solutions without the developing agent. These then keep almost indefinitely; the developing agent (in this case, brenzcatechin and/or pyrogallol) is weighed out separately just before development and added to the working solution as the final step. This way, it is impossible for stale developer to ruin a film, so there is no longer a shelf-life issue.
Differences between pyrogallol and brenzcatechin:
Pyrogallol produces a yellow-green stain, brenzcatechin a brown one; the highlight gradation on variable contrast paper is significantly reduced by pyrogallol and not noticeably so with brenzcatechin.
Pyrogallol must be agitated at least every 30 seconds; brenzcatechin can be left for stand development without disturbance.
To see what a PMK negative looks like, check out the first PDF ‘Tanol&Co..’ here at wm:
http://www.moersch-photochemie.de/content/knowhow
Here are some PMK photos:
http://edkrebs.com/
If you can read English and want to delve deeper, search for Sandy King (nickname sanking) and Patrick Gainer (nickname gainer) on apug.org, among others; here are a few links:
http://unblinkingeye.com/Articles/PCat/pcat.html
http://www.apug.org/forums/forum37/27497-new-pyrocat-m-experiences.html
http://www.jackspcs.com/pmk.htm
Here is my approach to pyrocatechol (Pyrocat-MC):
For testing, a small batch of 50ml Part A- (minus because it contains no Brenzcatechin):
50ml demineralised water at 20°C
0.4g triethanolamine
0.125g metol
0.2g vitamin C
Must be left to react for 1 day before use and will keep for at least 1 year even when partially filled (add lighter fluid if necessary).
Working solution for 450ml at a ratio of 1:1:100:
450ml demineralised water
4.1g sodium carbonate
4.5ml Part A-
0.23g catechol
Connoisseurs will notice the absence of propylene glycol: I don’t need it here. The brucatechin, which is to be protected by this, is only added shortly before development.
Example of development times:
CHS25 on N: Dilution 0.5:0.5:100 60 mins 20°C Agitate for the first minute, then only every 15 mins, exposure as for 12 DIN
Regards, Wolfgang
