Review (5/5): high purity alum, nice fine powder with no lumps or debris
If you're looking for technical grade alum at a good price, this is a great choice. It's high purity, and flows nicely as a powder. It wets easily, and doesn't have any lumps or impurities noticeable. Buying thee bas of alum ends up being far less expensive than buying little jars of it in the spice section of grocery stores. It's not labeled for consumption, so it's probably best to stick to using it for things other than cooking with, although it seems to be identical to the grocery aisle stuff.