[AndyGirlSays]

Hello everyone,

I am considering selling potassium alum stones for deodorant use. The plan is to grow the crystals myself, however I wouldn't know how to go about polishing them so the surface is smooth and therefore can be applied under armpits. I thought of using sand paper but I'm not sure if that's too rough.

Also, if you have grown alum crystals before, how big did you gent them to be?

Thanks!

[Arkcon]

Well, they're water soluble, and meant to be so they'll function as required.  So perhaps a wet cloth will smooth the sharp edges to be like the commercial products?

How big the crystals will grow is up to your skill and willingness to spend time on this craft.

Best of luck.  And post your pics for us.

[AndyGirlSays]

Update: the wet cloth was not effective. I will next try with the sand paper

[Corribus]

I really don't know anything about this topic but polishing a crystalline material to take rounded shapes can be challenging because cleavage happens only along crystal planes. 

[billnotgatez]

I have an inexpensive Ball mill used by hobbiest to polish stones.
It is similar to the one in this video
https://www.youtube.com/watch?v=CyBa-y3fEjY
[at 3:50 into the video is the machine in action]
The length of time you tumble determines if you end in a powder or a polished stone.
The shorter the time the less the abrasion.


WIKI has some discusion you might find interesting
Ball mill
https://en.wikipedia.org/wiki/Mill_(grinding)#Ball_mill

GOOGLE gives you lots of results for
Ball mill

Maybe you can polish your crystals into round stones (an experiment).
Hopefully they will not just turn into powder.
The mill looks simple enough to construct (I purchased mine).
I am thinking that by ball milling you would get some powder and some polished stones.
You can always do the crystallization again on the powder.