Yes. Sorry to not specify that.

Here's what Wall said in the 1912 Dictionary of Photography: "Chrome Alum...soluble 1 part in 10 cold water...It is used for hardening gelatine, as, for example, in the preparation of emulsions for dry plates to prevent frilling... Potash Alum..It is used for rendering the films of gelatine less liable to mechanical injury, by hardening them, and also clears them from stains. Solubility: 9.5 in 100 of cold water, 10 in 8 of boiling water..."

I take this to mean that chrome alum was traditionally used as a final addition to the emulsion itself, and that potassium alum was used in hardening baths. If so, it still needs some investigation to see if that would work for us. "Alum" just went on my grocery list. I've never used chrome alum in any of my emulsions, so the issue about its availability has slipped under my radar. Thanks for bringing this up .