Test 1
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.
Test 2
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.