The low-contrast developer POTA is excellent for getting normal contrast results and a wide dynamic range when using inherently high-contrast films such as Tech Pan and (nowadays in my case) Washi-S. However it is a bit awkward to use as you need to make it up and let it cool each time, then use it immediately or it will go off.
The components of the working solution are 30 g/l Sodium sulphite and 1.5 g/l Phenidone. Normally you dissolve the sulphite in hot water, then dissolve the Phenidone in the same solution, and cool it before use. The Phenidone is always reluctant to dissolve and the usual advice is not to worry about a bit being left undissolved, which I always think is a bit untidy.
What I do know, though, is that Sodium sulphite solution is reasonably stable on its own, and Phenidone dissolves easily in alcohol (ethanol) and seems to keep at least for months as a 15g/l solution in ethanol. I have a licence to use small quantities of "Industrial Denatured Alcohol" as it is called in the UK, which is what I use for this. It is better than the regular domestic methylated spirit as it doesn't have a dye or pyridine (smell) added, and it is reasonably dry - the domestic spirit has some water in it. I haven't tried either domestic methylated spirit for this developer, or isopropanol, but they might work. Further experiment needed there.
Here is my experimental formula based on all this:
Make two separate stock solutions -
Solution A is 150 g/l Sodium sulphite (anhydrous) in water
Solution B is 15 g/l Phenidone in alcohol.
Both of these should keep for a few months and possibly more.
To make a working solution, for each 100 ml ...
Take 70 ml water at about 25°C
Add 20 ml of A and mix well
Add 10 ml of B slowly, mixing as you go.
The result should be a clear pale yellow liquid, or maybe slightly cloudy which is still OK. It should also be at about 20°C, if not, next time adjust the temperature of the starting water. Use immediately.
Typical development time is 12 minutes with normal intermittent agitation in a tank, adjust to suit your own conditions.
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