I was thinking last night about @albada
saying a few times that I should try metaborate in glycol. Referring to the solubility numbers I could find, it doesn't really pencil out as mentioned a few posts back. But I found some numbers for borax that showed that solubility might actually be higher
in glycol than in water and I thought that might be even more true for metaborate. And then I was thinking last night that the solution will of course not be only glycol and metaborate: it will also contain ascorbic acid and phenidone. And actually that amount of acid could substantially change the solubility of sodium metaborate. So thanks to Mark (@albada
) for mentioning it again. I did an experiment this morning (day off) and was able to get about a 50% solution of metaborate in glycol once the ascorbic acid was added. I tested the following:
- 6ml of propylene glycol
- 3g sodium metaborate
- 0.7g ascorbic acid
- 0.03g phenidone (from 2.5% glycol solution)
- Stirred and heated into solution
This translates to a full formula of (DO NOT USE):
- 100ml propylene glycol
- 50g sodium metaborate
- 11.67g ascorbic acid (target is 12)
- 0.5g phenidone
This turns out to actually be too much
metaborate and the resulting pH is too high at about 9.25
. Knowing this was too high, but wondering what effect that would have on times and density, I tested with a small strip of Ilford Delta 100 and backed the time down to 6 mins 15 secs at 20C. Resulting clip density was way too high at about 2.5
and those are unusable dev times for other films (e.g. Fomapan would be like 4 mins).
But it looks like there is a possible route there to a working developer.
I did a further test to try to narrow in on the amount of metaborate needed to match the pH. I took 6ml of the PC-512 developing agents and added to 300ml of water. I then added small amounts of sodium metaborate and measured pH until I got to about 8.4. This is close to the borax version. I then tested a leader of Ilford Delta 100 for 6 mins 40s at 20C, the time I would normally use. I got a density of 2.10, which is just slightly under what I would normally get. I then developed a full roll in:
- 300ml water @ 20C
- 6ml PC-512 concentrate
- 1.2g sodium metaborate
Since the density was slightly low, I ran the short film clip for 7 mins. Results look pretty good. Eyeballing it I would say base + fog is a little higher, and maybe density a bit lower. Will post better numbers when the film is dried and I can measure it and scan it.
View attachment 332382
The idea then would be to try to make a single concentrate with that amount of metaborate. Assuming that it doesn't change its pH substantially when combining with glycol in heated solution.