Stull Charts and Limit Formulas

Stull Charts

Original Stull Chart

Original Stull Chart

The Glazy Stull Chart overlay was inspired by the work of R.T. Stull and Matt Katz. Note: The Stull chart was created for glazes with a flux ratio 0.3 R2O: 0.7 RO and fired to cone 11. There may be variations in the chart for glazes with different flux ratios fired at different temperatures.

For more information, see R.T. Stull's original article in Transactions of the American Ceramic Society, Volume 14, pages 62-70.

Also see Matt Katz's Introduction to Glaze Formulation Online, Robust Mid-Temperature Glazes and How Glazes Melt.

R2O:RO Ratio

The ratio of R2O to RO oxides has implications for glaze stability and expansion.

Matt Katz has demonstrated that a 0.3 R2O: 0.7 RO ratio produces the most robust glazes at a range of temperatures.

Also see Matt Katz's Introduction to Glaze Formulation Online, Robust Mid-Temperature Glazes and How Glazes Melt.

Glaze Limit Formulas

Note: As of March 2016 glaze limits are being removed from Glazy in favor of the Stull chart. The Stull chart seems to be a more reliable and descriptive guide than glaze limits. The glaze limit table chart below is retained for reference.

Glaze Limit Formulas are general guidelines for stable, functional base glazes. There are a wide range of published limit formulas, and a lot of controversy surrounding them. You will notice that many non-functional, decorative glazes will exceed glaze limits. If your functional glaze recipe exceeds a limit range it does not necessarily mean that your glaze is not safe, rather that you should pay attention to those oxides and perhaps consider modifying the recipe. Conversely, you should not assume that your glaze is stable simply because it falls within a glaze limit range.

RO/R2O (Fluxes) R2O3 (Stabilizers) RO2 (Glass Formers)
Name KNaO Li2O PbO ZnO CaO MgO BaO SrO Al2O3 B2O3 SiO2
Δ5-6 Val Cushing Glossy 0.05 - 0.6 0 - 0.5 0 - 0.6 0 - 0.15 0.05 - 0.6 0 - 0.1 0 - 0.15 0 - 0.15 0.1 - 0.3 0 - 1.0 1.5 - 4.0
Δ5-6 Val Cushing Satin 0.05 - 0.35 0 - 0.15 0 - 0.4 0 - 0.3 0.05 - 0.7 0 - 0.35 0 - 0.35 0 - 0.35 0.2 - 0.4 0 - 0.5 2.0 - 3.5
Δ5-6 Val Cushing Matte 0.05 - 0.3 0 - 0.1 0 - 0.2 0 - 0.4 0.05 - 0.8 0 - 0.45 0 - 0.5 0 - 0.5 0.2 - 0.5 0 - 0.5 2.0 - 3.0
Δ5-6 Hesselberth & Roy 0.01 - 0.03 0 - 0.2 0.2 - 0.6 0 - 0.3 0 - 0.2 0.25 - 0.4 0.15 - 0.35 2.5 - 4.0
Δ9-10 Val Cushing Glossy 0.05 - 0.5 0 - 0.4 0 - 0.15 0.05 - 0.8 0 - 0.15 0 - 0.15 0 - 0.15 0.2 - 0.5 0 - 0.5 2.0 - 6.0
Δ9-10 Val Cushing Satin 0.05 - 0.4 0 - 0.2 0 - 0.4 0.05 - 0.8 0 - 0.5 0 - 0.5 0 - 0.5 0.25 - 0.6 0 - 0.4 2.0 - 5.0
Δ9-10 Val Cushing Matte 0.05 - 0.3 0 - 0.1 0 - 0.5 0.05 - 0.9 0 - 0.6 0 - 0.6 0 - 0.6 0.25 - 0.8 0 - 0.2 2.0 - 5.0
Δ9-10 Hesselberth & Roy 0.1 - 0.3 0.3 - 0.7 0 - 0.4 0 - 0.3 0.3 - 0.6 0 - 0.3 3.0 - 5.0

There are many articles concering glaze limits, some notable ones are:

Digitalfire Limit Formulas and Target Formulas Frog Pond Pottery Glaze Stability Literature