Obsidian Aqua - mixin sodiums and potassiums

[esearing]

For those who have used OA, If I made my part A with Sodium Metabisulfite, can I use Part B made from Potassium Carbonate (Pyrocat HD-part B ) ?
Or do the metabisulfite and carbonate need to be both sodium or both potassium?

[Andrew Tymon]

https://www.largeformatphotography.info/forum/showthread.php?87166-Obsidian-Aqua-catechol-staining-developer

[esearing]

Read it 3 times now....

Jay indicates to use same "Dilute 1:500 with 6.66% carbonate solution (sodium or potassium, depending on which metabisulfite is used in the OA stock solution). " But the darkroom cookbook says Potassium and Sodium Carbonates can be substituted as an accelerator in developers ( adjusting for volumes/measures).
Thus why I asked for people who have used it and not a cut/paste reference.

[jnantz]

sadly i have never used the developer but
if you go to the hypercat website which has info on it ( i think it's jay's blog )

Dilute 1:500 in a 0.666% solution of potassium carbonate (6.66g/ liter), or a 0.5% solution of sodium carbonate (5g/liter).
https://hypercatacutancedeveloper.blogspot.com/2012/07/obsidian-aqua.html
sorry for just cutting and pasting with no experience..
john

[esearing]

The answer is Yes you can. I made a small batch at 1/2 strength for part A using 1/10th the suggested weights for 1 Liter. I had a hard time dissolving 25g of cachetol in just 75ml of water so I increased the water to make 200ml, and created what I now call OA/2-A. Logic dictates I will use 2ml of part A instead of 1ML as Jay suggests. For my part B I had some Pyrocat HD part B which is 750g/liter Potassium Carbonate for a stock solution, a little richer than the PC stock 666g/liter the recipe calls for. Since I use this in my tank for Pyrocat HD at 5mlA+5mlB+500mlW FOR 4 4x5sheets I figured I could reduce part B to 4.4ml in 500 with OA. Then came the realization I don't want to burn 4 sheets so I just loaded one. In theory for one 4x5 sheet I should be able to reduce A and B and still get a good negative.

I won't give all the gory details but my third round shows the most promise. it may be a bit over-developed but has useable contrast and density. I ended up using 2ml OA/2-A + 4.4m HD-B +475ml water 12:30 minutes at 70 degrees F. 3 minute agitations after 2minute initial.
A weak mixture of 1ml my part A +3ml B was too dilute or would need long processing times like Steve Sherman's EMA Method.