Alum is a generic term for many sulfate salts:
Classicly alum was (is) Aluminum sulfate , Al2(S04)3-18 H2O
called papermakers alum. or Aluminum potassium sulfate KAl (SO4)2
-12H2O or Sodium aluminum sulfate, NaAl(SO4)2-12 H2O, this is
mostly used as a leavening agent in bread (baking powder). There
are other industrial uses as a coagulating agent in water
purification or waste water.treatment etc.
I notice that the cucumber pickle alum in local markets is now
Ammonium sulfate. It can also be a sulfate salt of other metals.
Confused ??? Me too, as I don't know that it really makes any
difference which is best used as a metal pickle and I am a