A ceramic glaze chemistry calculator normalizes raw glaze recipes into Unity Molecular Formula (UMF), calculates the silica-to-alumina ratio, and plots the result on an interactive Stull Chart to predict whether the fired surface will be glossy, satin matte, or dry matte.
Normalized UMF Breakdown
| Fluxes (R2O + RO) = 1.0 | Stabilizer | Glass Formers |
|---|
Ceramic Glaze Mixing Equipment
Glaze chemistry requires absolute precision. If your flux ratio is off by just a few percent, your glaze could craze or run off the pot entirely. We strongly recommend using a high-precision digital gram scale (0.1g accuracy) to weigh your materials accurately. Once your dry materials are batched, they must be thoroughly integrated into the water. A standard drill with a stainless steel glaze mixing paddle will ensure the suspension is completely homogenous before you pass it through an 80-mesh sieve.
Understanding Unity Molecular Formula (UMF) & The Stull Chart
In ceramic chemistry, a glaze recipe written in percentages (e.g., 30% Silica, 20% Whiting) is useless for predicting how the glaze will melt in the kiln. Because different raw materials have vastly different molecular weights, you must convert the batch recipe into its Unity Molecular Formula (UMF). UMF categorizes the molecules by their role in the melt: Fluxes (which melt the glass), Stabilizers (Alumina, which keeps the glass from running), and Glass Formers (Silica). The UMF standard dictates that all Fluxes must sum to exactly 1.0. Once normalized, the ratio of Silica to Alumina determines the fired surface of the glaze. In 1912, R.T. Stull mapped these ratios onto a biaxial chart for Cone 11, revealing distinct zones for Matte, Satin, and Gloss glazes, as well as zones prone to crazing (cracking) or under-firing. SegerScale automatically calculates these normalized flux ratios and plots your glaze directly onto the Stull Chart, allowing you to visually predict the surface texture and stability of your glaze before you waste time and materials running physical test tiles.
Frequently Asked Questions
What is Unity Molecular Formula (UMF) in ceramics?
UMF normalizes a ceramic glaze recipe so that all flux oxides (RO/R2O group — Na2O, K2O, CaO, MgO, etc.) sum to exactly 1.0 moles. This standardization lets you directly compare glaze formulas regardless of batch size. From UMF, you can read the silica-to-alumina ratio, predict surface quality, and identify crazing or shivering risk.
What does the Stull Chart show for ceramic glazes?
The Stull Chart plots SiO2 (silica) on one axis and Al2O3 (alumina) on the other, with zones indicating predicted surface quality: glossy, satin/matte, dry matte, and crawling risk. High silica with moderate alumina produces gloss. Reducing silica moves toward matte. The chart helps you adjust recipes without endless test tiles.
What causes glaze crazing on pottery?
Crazing occurs when the glaze has a higher thermal expansion coefficient than the clay body — as both cool in the kiln, the glaze shrinks more and cracks under tension. Fixing it requires reducing the glaze's expansion by increasing silica, decreasing alkali fluxes (especially Na2O and K2O), or switching to a clay body with higher expansion.