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Published Dec 20, 2018

Today, we live in an age of super abundance of ceramic raw materials. Innumerable clays and glaze materials offer us a bewildering array of choices. Far from understanding glazes and these materials as familiar rocks, feldspars, and clays, each with unique personalities, we know them only as white, gray, or brown powders neatly packaged in uniform bags.

But we all know that getting to know them better can only improve our work. Happy learning! - Jennifer Poellot Harnetty, editor

There are probably as many kinds of clay as there are riverbanks, creekbeds, roadcuts, abandoned coal mines and backyard gullies, but most of the clays that many of us use on a regular basis are commercially mined.

Because not all materials are available through all suppliers, this chart is meant to provide data for the most common clays used in recipes you are likely to come across. You can use these data to compare the materials available through your supplier, or those you have on hand, with materials in the published recipes.

While the satisfaction, discovery and personal control that is possible through prospecting and processing your own clay are certainly valid reasons for the effort, most of us rely on the consistency and (relative) reliability of materials mined in large quantities. Even though the reasons for using commercially mined clays are most often based on a desire for a trouble-free product, the properties of clay as a natural material can make this goal somewhat elusive.

The following chart contains recent information, however, because the chemical and physical makeup of naturally mined materials can change across a given deposit, this chart is meant to be used as a starting point for clay substitutions. In order to precisely recalculate a recipe using a substituted clay, you will need to obtain a current data sheet for all materials you purchase from your supplier.

Please note that the clays are presented in alphabetical order, and the formulae are presented with alumina (Al2O3) in unity (totaling 1). This makes it easier to immediately see the ratio of alumina to silica, and also more accurately compares the relative amounts of all other components in the clays.

Unity Molecular Formulas of Clay Materials

Primary Function of Common Ceramic Raw Materials


MaterialGlaze FunctionSubstituteComment
Barium CarbonateFluxStrontium carbonate 
BentoniteSuspension agentBall ClayDo not exceed 3%
Bone AshOpacifier  
BoraxFlux, glassmakerBoron frits 
Chrome OxideColorant Green
Cobalt CarbonateColorantCobalt oxideBlue
Copper CarbonateColorantCopper oxideGreens, copper reds
Cornwall StoneFlux, opacifier  
Custer FeldsparGlaze corePotash feldspar (G-200) 
DolomiteFlux, opacifierWhitingMany brands
EPK KaolinAlumina, opacityKaolin 
Ferro Frit 3110Glaze core, fluxPemco P-IV05, Fusion F-75Crystalline glazes
Ferro Frit 3124Glaze core, fluxF-19, P-311, Hommel 90Boron frit
Ferro Frit 3134Glaze core, fluxF-12, P-54, Hommel 14Boron frit
Ferro Frit 3195Glaze core, fluxHommel 90, Fusion F-2Complete glaze
Ferro Frit 3269Flux, glaze corePemco P-25 
Ferro Frit 3278Flux, glaze coreFusion F-60, Pemco P-830 
G-200 FeldsparGlaze corePotash feldspar (Custer) 
Green Nickel OxideColorantBlack nickel oxideBlues, tan, browns, greens, grays
Kentucky OM4 Ball ClayAlumina, opacityBall Clay 
Kona F-4 FeldsparGlaze coreSoda feldspar 
Lithium CarbonateFlux  
Magnesium CarbonateFlux, opacifier Promotes crawling
Manganese DioxideColorant Purple, red, yellow-brown
Nepheline SyeniteGlaze core  
Red Iron OxideColorant Celadon green to brown
SilicaGlass former, glaze fitFlintUse 325 mesh
SpodumeneLithium glaze core  
Strontium CarbonateFluxBarium carbonate 
TalcFlux, opacifier Many brands
Tin OxideOpacifierZircopax 
Titanium DioxideOpacifier  
WhitingFlux, opacifierWollastonite, DolomiteMany brands
WollastoniteFlux, opacifierWhiting, dolomite 
Wood AshGlaze core, flux, colorantWhitingResults vary by type
Zinc OxideFlux, opacifier  
ZircopaxOpacifierSuperpax, Ultrox 



1. Substituting glaze ingredients may alter color, texture, opacity, viscosity, and/or sheen, as well as create pinholing, crazing, black spotting, and/or pitting. In most cases, additional adjustments to other ingredients need to occur when substituting.

2. Test and record your results.

3. Materials vary from supplier to supplier and batch to batch.


**First published in 2010