Thursday, July 5, 2012

Obsidian Aqua

I get a lot of inquiries about sourcing the ingredients for Hypercat from people living in places where propylene glycol is not available locally, and expensive to ship, and so I started thinking about a water-based version that could be sourced locally in most places, requiring perhaps only the catechol to be shipped. I call this version Obsidian Aqua.

Obsidian Aqua

Distilled water                                750ml
Sodium or potassium metabisulfite      20g
Catechol                                          250g
Distilled water to                             1 liter

Dilute 1:500 in a 0.666% solution of potassium carbonate (6.66g/ liter), or a 0.5% solution of sodium carbonate (5g/liter).

This is a very concentrated developer with excellent keeping properties, and gives results identical to Hypercat. I give options for using either sodium or potassium compounds, as availability differs, and results are identical.

Handling OA is a little different than handling Hypercat. Hypercat is best dispensed by a measuring syringe, and while this will also work with OA, because of the smaller volumes used, I find a pipet to be most convenient. I bought a precision one like this:

and a latex bulb like this:

The pipet is 1ml and graduated in .1ml, making it easy and accurate to measure out the 0.6ml for making up 300ml of 1:500 working solution for 35mm film, or 1ml for making 500ml for developing 120 film. If you normally make up larger volumes of working solution, higher capacity pipets are available. 

There are a number of ways to handle the carbonate. if you always make up a liter at a time, you could add 1 level teaspoon of carbonate to 1 liter of water, and get repeatable results, or you could make up a stock solution (I use a 66.6% solution of potassium carbonate) and dilute it, or make up a ready to use solution of 0.666% potassium, or 0.5% sodium carbonate. The important thing is that the working developer contains 6.66g of potassium carbonate, or 5g of sodium carbonate per liter. 

Development times should be the same as Hypercat, provided you're using the same mix. 

2.5ml of Hypercat A = 1ml of Obsidian Aqua A
OA 1:500  = Hypercat 1:200, using the same carbonate content for both.  

Some starting point development times for OA 1:500 are:

medium to slow films: 9:00 - 12:00, 70F, 10 seconds agitation/ 3:00

400 speed films: 12: -15:00, same as above

Kodak Technical Pan, and other document-type films: 1:1000, 15:00, 70F, agitate 10 seconds/ 3:00

I'll follow with some examples.


Regular Rod said...

Jay is it essential that the sodium carbonate solution is made with distilled water? I have obtained catechol and sodium metabisulphite in sufficient quantities to make 1 litre of concentrate and have distilled water to make it with.

I also have obtained sodium carbonate but do not have 500 litres of distilled water available. Is it safe for me to make the "Solution A" concentrate with distilled water as you describe and then to make the working solution to use 5% sodium carbonate solution using tap water?

Tap water in our area is quite safe to use with D76, HC110, 510-PYRO and DiXactol working solutions.

If I have to use distilled water throughout with Obsidian Aqua it will push the cost up quite a bit and storing the made up 5% sodium carbonate solution will be awkward too.

Any helpful advice will be much appreciated. Thank you.

Regular Rod

Unknown said...

Hi RR,

It's not necessary to use distilled water for the carbonate or working developer solutions -- just for the OA stock solution.

In practice, it's more conveninet for most people to make a stock solution of the carbonate. Sodium carbonate can be made up in a 20% concentrate (200g/ liter). Potassium carbgonate is much more soluble. Use a 20% solution of sodium carbonate to make up 1 liter of working solution of OA as follows:

Tap water- 750ml
20% sodium carbonate solution-25ml
OA stock- 2ml
Top up to 1 liter with tap water
stir and use immediately.

I hope that clears it up, but feel free to ask any questions that might come up.

Good luck!


Regular Rod said...

That's great Jay. Thank you very much.


Unknown said...

No Problem, RR -- I'm eager to see what you do with it!If you get something you like, I hope you'll consider posting examples here.

Regular Rod said...

Hi Jay

Finally got round to making up a batch and shared it with Steve Barnett, so expect to see some of his results soon. Jumped in head first and processed two different films at once as per DiXactol...

A spool of Ilford Pan F Plus exposed in the HolgAgon and a spool of ADOX CHS 25 Art exposed in an Agfa Record III. These were developed for 12 minutes @ 20 deg. C using a semi-stand routine that is easy to remember and keep track of when processing.

How to post examples here?


Unknown said...

Hi RR!

I bet your negs are incredibly sharp! Those are both sharp films, and semi-stand is extremely low frequency agitation.

To post images, just email them to me, along with any data and text, and I'll be happy to post it. Don't know an easier way, but I'm open to suggestions.

Thanks for the note. I'm looking forward to seeing your results!

Be well,


Unknown said...
This comment has been removed by a blog administrator.
Unknown said...

Hi Jay, I finally had an opportunity to mix up some OA, and I was quite pleased wit initial results. Negative was fulling exposed although a tad on the thin side, which can easily be rectified. Very sharp to the eye. I appreciated the fact that only 3 chemicals are required.
I'll have to print the negative (FP4 8x10, EI 64) to get a better feel.
I mixed in 25ml of the 20% sodium carbonate solution and 5ml OA (2ml seemed a bit piddly) into 750ml tap water and topped up to 1 litre. I developed for 15:00. 21 C.

Unknown said...

Hi Andy,
Thanks for posting your data. It's hard to advise without seeing your negative, and you're probably aware that stained negs print with more contrast than they look like they should. I like thin negatives, provided there's adequate shadow detail, and I can get the contrast I want in printing. If you have trouble getting a good print, you can extend development time, or increase agitation frequency, or increase processing temp, etc.
Good luck, and I hope you'll let us know how your neg prints.

morle said...

Hi Jay,

Thank you so much for your work and making this public.

I just finished my first run of processing 6 sheets of 8x10'' Fuji blue sensitive x-ray film in 2gallon tanks for 32 min using the geometric agitation sequence. The results are very promising but overdeveloped. I used 6.66g of sodium metabisulfite per liter as suggested in your large format photography post.

I like the long processing time because the results are absolutely homogenous.

Could I reduce the amount of sodium metabisulfite to reduce density?

What is the minimum stock solution A for a sheet of 8x10''? Could I work with even more diluted developer?

It looks like this is the first developer that I used on x-ray that really works. Yeah.

Christoph Morlinghaus

Unknown said...

Hi Christoph,

I assume you meant to write sodium carbonate and not sodium metabisulfite?

32 minutes is about 3X normal development time, so some adjustment to the developer will need to be made to get normal results. You can experiment with decreasing the concentration of carbonate, but too much of a decrease will begin to affect film speed. You could also decrease concentration of part A, but not by much, I don't think. You could try 1ml/ liter, but I would go much beyond that. You could also use a lower processing temperature, but I wouldn't go much below 18C. It might be necessary to use all three controls to get normal development time up to 32 minutes.

Good luck!