Limit Formulas

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's Limit Formulas and Target Formulas
• Frog Pond Pottery Glaze Stability Literature

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