With more or less the same philosophy I followed for Coffee Black, a only coffee developer with 20g/l of coffee and pH=11,4, I tried to make the same with Vit.C. The first time I diluted some 10g/l Vit.C and tried to rise its pH to 12 what I succeeded using sodium hydroxide. The second time I found out that I was very lucky in the first time. It is not that easy to achieve pH=12, it will be more or less than 12. Back to internet pool searching for other's experiences with Vit C. And here I found the solution to my problem: Patrick Gainer. Patrick advices us to join Vit.C in the buffer solution and not the contrary.
So, I started by making a buffer solution of pH=12 with sodium carbonate only (50g/l is enough). Then I joined Vit C until I see that the pH will strat to drop from 12. Stop! 10 g Vit. C. I may resume then the recipe as follows:
50g Sodium Carbonate
5g Vit. C
Water to make 1 liter
It is a one-shot developer like others I described here. Development time is also 60 minutes and gives no fog and little grain. The film will not have deep blacks, looks much less contrasty than Coffee Black and shows that Vit. C can work together with coffee to make general purpose developers.