The original Cornwall Stone Mine is now closed, and this material is now produced synthetically. Because it was mined from granite rock (traditionally, from the Cornwall area, UK), it is actually composed of a combination of minerals, and the ratio of these chemicals could vary somewhat drastically. This means that potters who used this material over long periods may notice different results when using the same recipes. An advantage of the substitute is the inconsistent variations that existed with the original material are no longer a problem for potters.
Cornwall stone is a low iron feldspar material used primarily as a flux in clay bodies and glazes. It has a more diversified selection of fluxes than other feldspars but also has one of the highest silica contents. By itself it does not melt as well as feldspars but it is popular in glazes for its low shrinkage and minimal contribution to defects.
Synonyms: Cornish Stone