Why does the red color not develop in the center glaze? This host recipe does not have the needed chemistry to develop the #6006 chrome-tin color (Mason Colors provide glaze unity formula guidelines: 6.7–8.4% CaO and avoiding MgO). This glaze recipe calculates to 9.8% CaO and 5% MgO. The MgO is the likely reason the red fails to develop. Yet this glaze produces excellent color with #6021 encapsulated stain (right). It isn't automatic that a strong red is achieved at just 5% encapsulated stain. The color is embedded in zircon crystals and aggressively melting KNaO, which this base recipe has very little of, attacks them and reduces color intensity.

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Mason is unusually information-open for the ceramic stain market. Their public reference guide gives compositions by listing oxides such as Co, Cr, Fe, Mn, Ni, Sb, Ti, Zn, Zr, etc., and then marks which oxides are involved in many stain families. It also gives practical compatibility notes, especially about zinc, calcium, firing limits and body-stain use. Their product pages often identify the crystal system/pigment class. For example, Mason 6630 Black is described as a chrome-iron-nickel black spinel formed by high-temperature calcination of chromium, iron and nickel oxides into a spinel matrix. Mason 6274 is described as a nickel silicate green olivine pigment formed from nickel oxide and silica. It is certainly helpful to know if your stain is, for example, a cobalt aluminate spinel, chrome-tin pink, zircon-vanadium blue, nickel silicate/olivine green, rutile yellow, etc. Mason’s technical table also lists CICP/color-index numbers, CAS numbers, chemical names, specific gravity, oil absorption, mesh residue and pH for some pigment lines. Of course, they don't publish oxide percentages, mineralizers, firing schedule, milling procedure, soluble salts, frit additions, trace impurities or batch tolerances. This being said, they are not completely alone; some others also publish such information.
Shown here are mugs I glaze using the G2934Y recipe with added Mason stains.
| Articles |
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
In ceramics color is often a matter of chemistry, that is, the host glaze must be compatible and have a sympathetic chemistry for the stain being added. Chrome-tin stains are a classic example. |
| Materials |
Stain 6006
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| Materials |
Mason 6021 Red Stain
An encapsulated red stain, it has proven better than any other red we have ever tried for glazes. And it works in bodies. |
| Recipes |
G2934 - Matte Glaze Base for Cone 6
A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte. |
| Glossary |
Encapsulated Stain
This is a type of stain manufacture that enables the use of metal oxides (like cadmium) under temperature conditions in which they would normally fail. |
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