Thanks for the kind comments.
I suspect that the numbers I quoted for limiting shutter speed and loss of effect over time are highly variable from one film to another.
Image stability: I wonder how noticeable the loss of latent sub-image is - as far as I know, the fewer the silver atoms clustered together, the less stable they are. The '50% loss of speed increase in a week' example I gave was a 'may' not a 'shall'. The stability of the image centres in the less exposed grains will depend a lot on the film itself, I guess. A few years ago I left some exposed APX 400 and Tri-X for a few weeks in the tropics before developing. The APX 400 lost a lot of shadow detail while the Tri-X stood up very well.
I don't know if the perborate would be re-usable. There are all kinds of things going on between borates and hydrogen peroxide and stuff so it might be that the pH falls over time and that the reduction-oxidation properties change. This particular aspect is getting outside my current understanding.
Sodium perborate forms an alkaline solution, hydrogen peroxide an acid solution. Bear in mind, if using a borate-peroxide mix instead of perborate, that commercial H2O2 may include an acid stabiliser.
Oh, Persil got its name from perborate-silicate.
(later addition: hydrogen peroxide is more stable in acid solutions than alkaline ones; pharmaceutical grade has low amounts of stabiliser, cosmetic grade has the most)
Last edited by Helen B; 01-28-2005 at 11:48 AM. Click to view previous post history.