Just measure th pH of a working solution of Hypercat and you will ifind that it is well over pH 12, about 12.4 or so from my tests.

Of course, my measuring instruments could be wrong, but they appear to be working ok because when I measure the pH of other developers, PMK for example, my measurments of pH 9.5 to 9.7 turn out to be very close to to the 9.6 that Hutchings reports.

It is certain that the combination of even small amounts of sulfite and ascorbic will kill the stain with pyrocatechin developers, unlike pyrogallol types which are obviously more resistant. However, what I am suggesteing is that the pyrocatechin based developer will allow much more ascorbic and/or sulphite without losing the stain if it is working at a higher pH.


Sandy


Quote Originally Posted by jdef
Sandy,

I don't think the pH of Hypercat is as high as you say. Ascorbic acid is about 10X more acidic than sodium metabisulfite, and neutralizes some of the sodium hydroxide in the working solution to form sodium ascorbate, so the pH of the working solution is not the same as the pH of the B solution alone. In any case, I've tested it using the B solution of Pyrocat HD with no significant difference in stain formation, maybe because potassium carbonate has a much higher buffer capacity than the weak solution of sodium hydroxide used with Hypercat, and is less sensitive to the addition of ascorbic acid. The sodium metabisulfite in Pyrocat HD might not reduce the stain appreciably, but when you start adding ascorbic acid, it doesn't take much before you'll see stain loss because of its addition with the metabisulfite. There is as much sodium metabisulfite in Pyrocat HD as there is ascorbic acid in Hypercat. If I was to add sodium metabisulfite to Hypercat, it wouldn't take much to begin to reduce the stain formation. I think that using both is redundant.

Jay