Obsidian Aqua, catechol staining developer

[Bob Farr]

Yes, Bob, that's right, 300/500= 0.6-- thanks for the correction. 0.3ml is what I used for Tech Pan, and that's a 1:1000 dilution, but the capacity is still valid. I shouldn't try to work from memory, and actually do the math!

Hi Jay,

Thanks for your reply!! So, if 0.6ml of stock is needed for one roll of 35mm film and to develop four sheets of 4x5 film. Then it seems that at least 2.4ml would be needed for twelve sheets of 4x5. It's important because I wish to have an adequate volume of OA for 5x7 and 5x12 film.

Thanks,
Bob

[Bob Farr]

Thanks Jay

[Bob Farr]

Hi Jay,

The working solution is 1;500ml, so I'll need to mix up liters if not gallons of part B [666gms of carbonate per liter] for a developing session??

Bob

[Jay DeFehr]

Hi Bob,

The working solution contains 6.66g/liter of potassium carbonate, or 5g/liter of sodium carbonate. Mix up only as much working solution as you need. For each liter of working solution, use 2ml of OA stock + carbonate as described above.

You can make a stock solution of carbonate, and for this potassium is more simple and direct than sodium carbonate, because it's more soluble.

Potassium carbonate stock solution:

Water 700ml
Potassium carbonate 666g
Water to 1 liter

Use 1ml of the above for every 100ml of working solution.

Sodium carbonate stock solution:

Water 700ml
Sodium carbonate 200g
Water to 1 liter

Use 2.5ml of the above for every 100ml of working solution

[Bob Farr]

Hi Jay,

This helps a lot to understand how to use OA. To recap-

If using sodium metabisulfite for part A then 200gms of sodium carbonate in part B resulting in a 1:2.5:100 dilution.

Does this fit with the original dilution of 1:500?? Or should the working solution be 0.1:2.5:100??

Or if using potassium metabisulfite for part A the 666gms of potassium carbonate for part B resulting in a1:1:100 dilution.

Does this seem about right??

Bob

[Jay DeFehr]

Hi Bob,

I'm afraid that's not quite right. The compound ratios would be:

OA + potassium carbonate 66.6% + water = 1 + 5 + 500

OA + sodium carbonate 20% + water = 1 + 12.5 + 500

To mix with 100 parts water, you'd need to divide everything above by 5, as in:


OA + potassium carbonate 66.6% + water = 0.2 + 1 + 100

OA + sodium carbonate 20% + water = 0.2 + 2.5 + 100


The above makes for easy calculation, as the numbers are all multiplied by the desired final solution volume in 100s of ml. For example:

To make 300ml solution

With potassium carbonate 66.6%, (0.2 + 1 + 100) X 3 = 0.6 + 3 + 300

With sodium carbonate 20%, (0.2 + 2.5 + 100) X 3 = 0.6 + 7.5 + 300

Make sense?

[Bob Farr]

Thanks jay,

Am glad that all of this is getting cleared up before I jump into this.

Bob

[Jay DeFehr]

No problem, Bob. There are a lot of numbers involved, and it can be confusing, but once you decide on a working method, you can forget about a lot of the numbers, and concentrate on your personal process. I use potassium metabisulfite in my OA stock, and a 66.6% potassium carbonate stock solution. It's easy for me to remember that I use a 1:100 dilution of my carbonate stock solution to make a working solution, and I always make the alkali solution first. Then I simply add 0.2ml OA stock/ 100ml of the alkali solution to make a working developer. But, just in case, I labelled my carbonate solution 1:100, and my OA stock 0.2:100. I also ignore the tiny error in beginning with the desired final solution volume of water. So, if I'm making up 500ml of developer, I start with 500ml of water, add 5ml of carbonate solution and stir well, and then 1ml of OA stock, and stir again. I end up with 506ml of solution, but this has no measurable effect on results.

Once you do this a few times, you stop thinking about it -- it's just automatic-- very quick and easy.

I always use the same 1:500 dilution of developer (except when developing document films), and control edge effects with agitation. Most films I've tested develop in 12:00, 70F, with agitation at 3:00 intervals, to produce good prints on G2-3 paper. These films include: Kodak TMY-2, Fuji Acros, Adox CHS 50, and 25, Ilford Pan F+, and Foma 100. Some films, Like Foma 400, require 15:00.

Good luck!

[John Fink Jr.]

Sounds excellent Jay, thank you!!

[Jay DeFehr]

Hi John,

I'm very happy with this developer. If you decide to give it a try, and have any questions, don't hesitate to contact me--

jdefehr@gmail.com