Unity Molecular Formula (UMF)

The Unity Molecular Formula, or UMF or Seger Formula, is a very useful way to compare glaze recipes because the analysis is based on the number of molecules rather than weight, and it is unified based on the fluxes. Therefore we can compare the amounts of stabilizers, glass-formers, and other oxides in terms of the fluxes. Its easy to compare different UMF analyses, as they are all unified in the same way.

Put in another way by Linda Arbuckle:

Silica is a glass former. Alumina modifies a glass. Fluxes reduce melting temperature. The Unity Molecular Formula (UMF) systematically relates these chemistries to each other in a useful glaze chemistry shorthand UMF shows the ratio of glass formers to fluxes and can be used to predict glaze behavior.

The fluxes are split into two different types: R₂O (or Alkaline Metals) and RO (Alkaline Earths).

There are two versions of the UMF on Glazy. The first is traditional UMF, which is the way most people (and glaze calculation software) have usually calculated UMF.

The second version is Extended UMF.

Traditional UMF Oxide Groups

R₂O Group: Na₂O, K₂O, Li₂O

RO Group: PbO, SrO, BaO, ZnO, CaO, MgO, MnO

R₂O₃ (Stabilizers) Group: Al₂O3

B₂O₃ (Special Case)

RO₂ (Glass-Formers) Group: SiO₂, ZrO₂, SnO₂, TiO₂

Other Oxides: FeO, Fe₂O₃, MnO₂, P₂O₅, F, CoO, Cr₂O₃, Cu₂O, CuO, NiO, V₂O₅, ZrO, HfO₂, Nb₂O₅, Ta₂O₅, MoO₃, WO₃, OsO₂, IrO₂, PtO₂, Ag₂O, Au₂O₃, GeO₂, As₂O₃, Sb₂O₃, Bi₂O₃, SeO₂, La₂O₃, CeO₂, PrO₂, Pr₂O₃, Nd₂O₃, U₃O8, Sm₂O₃, Eu₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃

Extended UMF

The “extended” UMF attempts to define roles for a broader range of oxides, for example CuO and CoO, that were previously viewed as secondary (e.g. “colorants”) and classified outside the unity as “other”. This version of the UMF is still a work in progress. It is based on the research of Matthew Katz and Rose Katz from Ceramic Materials Workshopopen in new window.

Rose Katz’s 2019 NCECA Lecture “COLORFORMS” discusses the roles of all major colorants:

Glazy's "Extended" UMF comes directly from Matthew & Rose Katz's Experimental UMF Calculator. This spreadsheet calculator can be downloaded here.open in new window

This Experimental Calculator is still a work in progress. Glazy will be updated as new information comes to light.

Extended UMF Oxide Groups

R₂O Group: Na₂O, K₂O, Li₂O, Bi₂O₃, CuO, SnO₂

RO Group: PbO, SrO, BaO, ZnO, CaO, MgO, MnO, Fe₂O₃, MnO₂, CoO

R₂O₃ (Stabilizers) Group: Al₂O₃, TiO₂, NiO

B₂O₃ (Special Case)

RO₂ (Glass-Formers) Group: SiO₂, ZrO₂

Other Oxides: FeO, P₂O₅, F, Cr₂O₃, Cu₂O, V₂O₅, ZrO, HfO₂, Nb₂O₅, Ta₂O₅, MoO₃, WO₃, OsO₂, IrO₂, PtO₂, Ag₂O, Au₂O₃, GeO₂, As₂O₃, Sb₂O₃, SeO₂, La₂O₃, CeO₂, PrO₂, Pr₂O₃, Nd₂O₃, U₃O8, Sm₂O₃, Eu₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃

https://www.youtube.com/watch?v=HyLjAg1_8_4

For more information about UMF and the importance of the flux ratio:

• Linda Arbuckle's Introduction to Glaze Calculationopen in new window
• How Glazes Meltopen in new window by Dave Finkelnburg
• Digitalfire's Understanding Glaze Calculationopen in new window

Oxides Used in Historical UMF Calculation

Daniel Rhodes "Clay and Glazes for the Potter":

Val Cushing's Handbook:

Linda Arbuckle's Glaze Calc Handout

Henrik Norsker, James Danisch: "Glazes for the Self-Reliant Potter"