Thanks to Alessandro and Dan for correcting my mistake: Ion exchange is indeed the principal mechanism HCA and other wash aids use. Emulsion swelling depends on pH. A bit of emulsion swelling might help the speed of the ion exchange a bit, but is not the most important aspect.
Nancy, I would use a fresh HCA bath after toning unless your workflow is such that you fix, HCA, wash, tone, HCA, wash, in which case, I would simply eliminate the first HCA bath. FWIW, I fix twice, washing and drying after the first fix and then collect larger batches of "keepers" for toning sessions. In these, I soak, fix2, tone (no rinse before the toner), HCA, and then wash.
Mix what you need of HCA for a single session. You can use spoonfuls of the HCA powder instead of making the intermediate stock solution as Ralph (I think...) mentioned above. I used to store the powder in a glass jar and spoon out what I needed for one or two liters at a rate of one Tablespoon per liter. I now use a Tablespoon of sodium sulfite with a pinch of metabisulfite per liter.
And, as Ralph and Dan, among others, point out, it is important to check your wash to make sure it is adequate, even with a wash aid.
Best,
Doremus Scudder
www.DoremusScudder.com
