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 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. That’s why we compiled our latest free download Ceramic Raw Materials: Understanding Ceramic Glaze Ingredients and Clay Making Materials. This helpful studio reference includes charts, guides, a glossary of raw materials, and a lot more to help broaden your knowledge of clay and glaze chemistry. Today I have excerpted a couple of pieces that you’ll want to keep handy in your studios, including a chart detailing the unity molecular formulae of common clays and an explanation of the functions of ceramic raw materials. Happy learning! – Jennifer Harnetty, editor.

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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 air-?oated 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.

For a printer-friendly version of the charts below, download your free copy of Ceramic Raw Materials: Understanding Ceramic Glaze Ingredients and Clay Making Materials!

Unity Molecular Formulas of Clay Materials

(click to enlarge)


(click to enlarge)



Primary Function of Common Ceramic Raw Materials
Material Glaze Function Substitute Comment
Barium Carbonate Flux Strontium carbonate
Bentonite Suspension agent Ball Clay Do not exceed 3%
Bone Ash Opacifier
Borax Flux, glassmaker Boron frits
Chrome Oxide Colorant Green
Cobalt Carbonate Colorant Cobalt oxide Blue
Copper Carbonate Colorant Copper oxide Greens, copper reds
Cornwall Stone Flux, opacifier
Custer Feldspar Glaze core Potash feldspar (G-200)
Dolomite Flux, opacifier Whiting Many brands
EPK Kaolin Alumina, opacity Kaolin
Ferro Frit 3110 Glaze core, flux Pemco P-IV05, Fusion F-75 Crystalline glazes
Ferro Frit 3124 Glaze core, flux F-19, P-311, Hommel 90 Boron frit
Ferro Frit 3134 Glaze core, flux F-12, P-54, Hommel 14 Boron frit
Ferro Frit 3195 Glaze core, flux Hommel 90, Fusion F-2 Complete glaze
Ferro Frit 3269 Flux, glaze core Pemco P-25
Ferro Frit 3278 Flux, glaze core Fusion F-60, Pemco P-830
G-200 Feldspar Glaze core Potash feldspar (Custer)
Green Nickel Oxide Colorant Black nickel oxide Blues, tan, browns, greens, grays
Kentucky OM4 Ball Clay Alumina, opacity Ball Clay
Kona F-4 Feldspar Glaze core Soda feldspar
Lithium Carbonate Flux
Magnesium Carbonate Flux, opacifier Promotes crawling
Manganese Dioxide Colorant Purple, red, yellow-brown
Nepheline Syenite Glaze core
Red Iron Oxide Colorant Celadon green to brown
Rutile Colorant Ilmenite
Silica Glass former, glaze fit Flint Use 325 mesh
Spodumene Lithium glaze core
Strontium Carbonate Flux Barium carbonate
Talc Flux, opacifier Many brands
Tin Oxide Opacifier Zircopax
Titanium Dioxide Opacifier
Whiting Flux, opacifier Wollastonite, Dolomite Many brands
Wollastonite Flux, opacifier Whiting, dolomite
Wood Ash Glaze core, flux, colorant Whiting Results vary by type
Zinc Oxide Flux, opacifier
Zircopax Opacifier Superpax, 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.

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