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We are a small NGO in Nepal working to help people after the recent earthquakes of 2015 and now the floods of this year's monsoon of 2017. There is a stone here that is used as an astringent/after shave when men go to the barber for a shave. Our agency would like to mold this stone into a small soap-shaped bar to sell as a fundraiser. As it turns out, it is an excellent hand sanitizer and I've used it for years, since moving to Nepal 7 years ago. This is the same stone being used for deodorant bars. It is called alum stone or fitkiri.

We will be ever so grateful for any suggestions. It melts at a low temperature, but we cannot get it to hold together as it solidifies. Every time I have shown a guest the stone they've been eager to have one. If we can mold it into a small shape it will help to keep many people from getting the typical traveler's stomach upset. This is even more important for people going up into the Himalayas.

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  • Do you know the chemical composition of the stone? I'm assuming alum indicates it contains aluminum?
    – LShaver ♦
    Sep 5, 2017 at 19:15
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    @LShaver en.wikipedia.org/wiki/Alum "An alum block sold as an astringent in pharmacies in India (where it is widely known as Fitkari (Hindi) or Phitkari (Urdu)"
    – Highly Irregular
    Sep 5, 2017 at 20:40
  • It looks like you can't. From revolvy.com/topic/Alum: When heated, they liquefy, and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains
    – user2451
    Sep 6, 2017 at 8:57
  • I don't think you can mould it, but one can relatively easily grow large single crystals of Alum (it is a popular childrens' science experiment). Google "growing Alum crystals" for info. I don't know how easy it would be to scale this process up however. Another alternative may be to press powder/fine crystals together - though you would need some form of binder and would need to invest in machinery.
    – aucuparia
    Sep 7, 2017 at 14:18

1 Answer 1

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There are a bunch of different materials called alum. The most common, is potassium aluminum sulfate.

KAl(SO4)2 * 12 H2O

The material is very soluble in hot water, and melts at 92.5 C (less than boiling point for water.)

Because of it's general solubility, I don't know if the stones sold are pure alum. You may want to add some form of filler that would reduce the water contacting the surface. I would suggest trying talc powder. (baby powder), or cabosil (fumed silica). Avoid organic fillers such as corn starch, husks, psyllium as they will likely mold or mildew.

Methods of prep: Haven't done this. This advice worth what you paid for it.

1a. Barely cover the bottom of a pan with water, and get it hot. Add alum crystal to it. As they dissolve, keep adding more. Continue until you have a temperature just under the melting point. A cheap electronic thermometer may be useful.

or

1b. Put alum in the upper pot of a double boiler, and let it heat with a lid on it until it melts and is clear.

  1. Stir in filler compounds. How much? Experiment.

  2. Pour into molds.

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