One of the easiest ways to categorize fluxes is by their major component. It must also be remembered that these are mined materials that have been minimally processed (usually simply being pulverized). Variations do occur at times, and mines do play out. Other sources of ash that can be used are reeds, grasses, straw, leaves, and so on. The high alkaline content, which acts as the flux in the glaze, is caustic, so some people wash the ashes before use. Washed ash does not flux as well as unwashed ash, and will require more ash content in the glaze.
Soda feldspar, such as the commercially available Kona F-4. Nepheline syenite: A high soda feldspar that included some potassium, has a lower melting temperature than soda feldspar and is useful in the mid-range temperatures. Often abbreviated to “neph sye” by many potters. Sodium carbonate: aka soda ash. Sodium chloride: aka table salt. Used in salt firing and vapor glazing in saggers.
Potash feldspars, such as Custer and G-200.Cornwall stone: aka Cornish stone. Contains mainly potassium, but also has sodium and calcium.Volcanic ash: Generally richest in potassium, but the chemical composition can vary widely. Always do a few test pieces when using a new bag of volcanic ash when mixing your own glazes.Potassium carbonate: aka pearl ash. Used mainly as a color modifier.
Lithium feldspars, such as spodumene and petalite.Lithium carbonate: The preferred source of lithium for crystal growth.
Gerstley Borate: No longer mined, but some limited amounts are still available. Synthetic replacements are available from many suppliers.ColemaniteBorax: Often used in raku glazes and to smooth out higher firing glazes.Boron-containing frits such as Ferro 3110, 3124, and 3134.
Whiting: aka calcium carbonate and lime. Used in high-fire glazes.Dolomite: A calcium-magnesium carbonate used in high-fire glazes.Wollastonite: A calcium silicate used in both clay bodies and glazes. Promotes strength and reduces shrinkage.Bone ash: aka calcium phosphate. Used to produce opacity and opalescence in glazes, as well as being a flux.
Magnesium carbonate: flux for high-fire range, increases glaze adhesion and viscosity. Used for matte glazes. Talc: Used as a flux in low-temperature clay bodies, and as a flux in both low- and high-fire glazes. Dolomite: A calcium-magnesium carbonate flux used in the high-fire range when both elements are desired.
Red lead and white lead: These are two forms of raw lead and are extremely hazardous in large amounts. Lead remains in the body indefinitely, resulting in cumulative amounts increasing with each exposure.Lead silicate and other lead frits: Fritted lead compounds are less dangerous than raw leads. They are still hazardous, however, and are best avoided.
