Common alum is sulphate of alumina combined with another sulphate, as potash, soda, etc.
"Scientific American Supplement, No. 362, December 9, 1882" by Various
Potash alum is most commonly used, soda and ammonia alums to a less extent.
"Human Foods and Their Nutritive Value" by Harry Snyder
They dye good but fugitive red with bichromate of potash, or alum.
"Vegetable Dyes" by Ethel M. Mairet
Potash alum saturated aqueous solution 5 c.c.
"The Elements of Bacteriological Technique" by John William Henry Eyre
Thus during the diffusion of alum, the sulphate of potash is separated from the sulphate of aluminium.
"The Mechanism of Life" by Stéphane Leduc
This was the common potash alum and uncombined with any carbonated alkali, and it passed into the stomach unchanged.
"Scientific American, Vol. XXXIX.--No. 24. [New Series.], December 14, 1878" by Various
Dissolve common (potash) alum, one ounce in a pint of tepid water.
"The Barnet Book of Photography" by Various
The rule indicates, also, that aluminium chloride would be better than the sulphate or than potash alum.
"Animal Proteins" by Hugh Garner Bennett