Catechol - Bill Bowes formula

So, I tried it the weekend before last, and it didn't do anything - no development, nothing. Tried it again this weekend, with some further advice from Bill Bowes, and bravo. It worked. Scanned today. Herewith some shots, FP4 developed for 14 mins in a 1:500 solution (the formula is at google search obsidian aqua, though on Bill Bowes advice I doubled the carbonate for the developing mix). The chemistry is easily available (other than the sulphite to stabilise the fixer; but even then, with one shot development, the fixer is easily available from any pool maintenance shop - and cheap)

 

 

 

 

 

 

 

The first two are barflys. The third, my stepson (who has global developmental delay). All done with an M3 and 35mm summaron (goggles). This stuff is good. Good negative density, good tonal range, not much grain. I'm going to try it some more. Regards, Arthur (apiarist1 - normally on the leica thread)

Credit for this developer goes to Jay Defhr. Obsidian Aqua (OA) is about as simple as one can get. Catecol & a common bisulfate for a preservative. Di water is used. I am now trying almost the same chemistry, but in Proplane Glycol, which Defhr labels Hypercat. First three rolls are almost identical to the OA. Do give either chemistries a try if you want to break into the pyro staining developers. There are some available pre-made, but these two are DIY. Bill

I forgot to mention that the activating carbonate can be from a chemist supply house or common washing soda (Arm & Hammer). Either is effective. Fixer demand is only that it be non acid.

Those look great! I've heard Bill mention pyro staining a few months ago and looked into it back then, but then promptly forgot about it. I've not been 100% happy with HC-110 but it's still kind of new to me and now I've got this big bottle of it...

...other than the sulphite to stabilise the fixer

Sodium or Potassium Sulphite is readily made from the metabisulphite form, used as a wine preservative or food-container steriliser, plus the addition of a small amount of sodium hydroxide (caustic soda, drain cleaner).

 

The transformation in solution is:

Na2S2O5 + 2NaOH > 2Na2SO3 + H2O

 

Using equimolar quantities, the yield is: 190g of sodium metabisulphite + 80g sodium hydroxide, gives 252g of sodium sulphite (+ 18g water). And those quantities can be scaled up or down as required.

 

Sodium hydroxide, being caustic and deliquescent, should obviously be handled with care!

 

If using potassium metabisulphite, the initial quantity should be raised to 222g, which results in a slightly greater amount of a mixture of sodium + potassium sulphite in solution. However, the overall activity should be the same.

Edited July 23, 2019 by rodeo_joe|1