Alternate Names: Pumicite
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Pumicite is composed of minute particles of volcanic glass. Pumicite is easily processed due to its fine in nature. Deposits resulted from volcanic eruption blowing large quantities of material into the air which settled in layers, sometimes in thicknesses which compressed to 30 feet or more. Volcanic ash particles are non-crystalline due to the quick cooling during formation. This material thus takes on the unique melting properties associated with a glass.
The chemistry is similar to granite or ryolite. Raw color varies and deposits can be found over wide areas of the central and western areas of North America. Volcanic ash materials vary widely in their chemistry, it is impossible to formulate a representative analysis, the one shown here may not be similar to your native material.
Some types of volcanic ash are balanced enough chemically that they can be used in amounts to 50% or more of the glaze batch. Most require the addition of fluxes and kaolin to form a glaze with reasonable firing and suspension properties.
More sample formulas of two well known materials:
Out Bound Links
In ceramic technology the term 'glass' is contrasted with the crystalline state, it is seen as a "super-cooled liquid". When crystalline materials solidify the molecules have opportunity to orient themselves in the preferred pattern during freezing whereas in a glass the random orientation of molecu...
In Bound Links
How to have a volcanic ash analysed and them use ceramic chemistry to create a glaze that contains the maximum possible amount of the ash for the desired effect
Joseph Herbert overviews the technical and practical aspects of this interesting group of materials
Mount Saint Helen's Ash
Mount Pinatubo Volcanic Ash
A glaze that employs ash from organic (e.g. paper, wood) or volcanic sources as a supplier of oxides (e.g. silica, alumina, soda, calcia). Many books deal with the preparation (washing) of organic ash batches (remember these materials are caustic) and provide example recipes. It can be difficult to ...