I missed the part about using Hypercat with the Pyrocat-HD stock solution so guess you are right about the pH not having a role in the stain.
My own tests do confirm that the amount of phenidone in the Pyrocat-HD formula is more than needs to be there, and the same is true of potassium bromide. I will most likely amend the formula at some point in the future, though from a practcial consideration there is not much to be gained but perhaps a slight increase in EFS.
BTW, my use of sodium metabisulfite over sodium sulphite has nothing to do with a desire to decrease the pH of the working solution. The metabisulfite is there to provide stability for the stock solution when mixed with water. For mixture in glycoal the sulpite can be eliminated, with just a very slight loss of energy. However, for many reasons I intend to promote the use of Pyrocat-HD primarily for mixture with water in stock solutions, where is has pretty impressive stability -- at least a year or more. Mixture in glycoal does offer some advantages, both in terms of stability and choice of ingredients, but so to does the convenience of mixture in water.
As for edge effects, there may be advantages to working solutions that are poorly buffered, but there are also disadvantages. With Pyrocat-HD adjacency effects are determined by type of agitation, and the working solution is well-buffered up to dilutions of about 2:1:400.
Originally Posted by jdef
Last edited by sanking; 01-27-2006 at 05:45 PM. Click to view previous post history.