Alum powders contain potassium bisulphate and alum.
"Encyclopaedia Britannica, 11th Edition, Volume 4, Slice 4" by Various
Ferric potassium sulphate, the common iron alum, K2SO4.Fe2(SO4)3.24H2O, forms bright violet octahedra.
"Encyclopaedia Britannica, 11th Edition, Volume 14, Slice 7" by Various
Another patent, taken out in 1879 by Heinzerling, specified the use of potassium dichromate and alum.
"Animal Proteins" by Hugh Garner Bennett