Alum as a Mordant

[elizabeth]

How important is it for the Alum mordant to be Potassium Aluminum Sulfate instead of Aluminum Sulfate?

I was looking at the Dharma sale dyes and saw someone complaining that the Alum w/out Potassium did not work as well.
She referred to a vendor site as her source, but when I go to the site the vendor is selling Aluminum Sulfate.

Does anyone have a preference? On Amazon, Jaquard's PAS is 3x the price for plain AS.

Thanks

[luvswool and dyestuff]

It depends on what you are dyeing. I have done a lot of research specifically on natural dyeing, so I can only speak about that with regards to alum. Aluminum sulfate is used as a mordant with protein fibers, like wool and silk. It is the same alum used in making pickles, so considered safe to use. I’ve not seen AS referred to as Potassium or containing potassium but I am not a chemist. All of the references I have used refer to the popular mordant as alum or aluminum sulfate.

There is another alum--aluminum acetate which is used as a mordant for cotton and other cellulose fibers.

I don’t know if that’s helpful or not, as I work mostly with natural dyes. Good luck (I would probably opt for the lower-priced AS to begin with re: Jacquard dyes…)