How to make a Geopolymer Crucible for Refining Gold

You can easily make a crucible for refining gold by using an ancient technology that was allegedly used to build some of the stone blocks used in the pyramids of Egypt. This technology was rediscovered in the 20th century by a chemical engineer from France named Joseph Davidovits who named it geopolymer. This material can take the place of both conventional concrete and many ceramics, but for the purpose of gold prospecting we shall limit this discussion to making high-temperature crucibles.

Pouring gold from a crucible
Photo by Allen Drebert

The activator fluid is made from 32% sodium hydroxide dissolved in water. The solution also contains 32% sodium silicate. The sodium hydroxide solution is made first by dissolving 32 g of sodium hydroxide in 100 ml of water that is allowed to sit overnight. The activator solution also requires 250 ml of a 32% solution of sodium silicate that can be mixed the next morning.

The completed activator solution contains 100 ml of the sodium hydroxide solution, and 250 ml of the sodium silicate solution mixed together. The activator solution has to be mixed with a pozzolan material of which there are several you can use:

Coal fly ash

Volcanic ash

Ground glass

Ground brick

Coal fly ash and volcanic ash and do not have to be ground, but the other materials have to be ground as fine as possible. The nice thing about making crucibles from this formula is it doesn't take much to make a workable crucible.

The process works like this:

To three parts of pozzolan material and six parts of sifted sand add enough of the activator fluid so that it makes a paste that has “zero” slump when it is mixed. Because of the highly corrosive nature of this mixture you should wear rubber gloves whenever you are handling the material.

The easiest pozzolan material for most people to acquire is either ground glass or a ground-up brick. Glass can be extremely difficult to grind unless you heat it first to red heat with a torch, and plunge it immediately into cold water. This makes it much easier to grind, and glass is one of the most readily accessible pozzolan materials.

The mixture is kneaded into a clay like mass that is then applied to a mold. Coat the surface of the mold with a film of vegetable oil so the crucible will not stick when you try to remove it. The mold should be made of wood that has been coated with a layer of shellac before being used. In a pinch you can use an ordinary drinking glass for a mold providing you cover it with a film of vegetable oil first.

The mold should be covered with about 1/4 inch of the geopolymer material that is allowed to set overnight before removing it from the mold. After the crucible is removed from the mold that is ready for use.

If you have difficulty in making the geopolymer material into a clay like mass you can add one part of calcined clay. It doesn't take much to make a single crucible and we usually use a teaspoon to measure the amounts we need. 

Getting the fixings together for this can present some problems, but the most difficult are getting the sodium hydroxide that is usually sold under its common name “lye” in hardware stores as a drain cleaner. Do not use any other drain cleaning compounds for this project. The other chemical that is hard to find his sodium silicate that also has a common name “waterglass.” If this chemical is not available locally it can be ordered from Sheffield Pottery in 1 pound quantities. Sheffield ships all over the United States and Canada.

It was probably a variation of this formula that the Japanese used to stop the leak in the nuclear reactor that was damaged by the earthquake and tsunami that struck Japan on 11 March 2011.

You can read much more about the science of geo-polymers and Pozzicrete and by going here!