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
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 Workshop.
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.
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
For more information about UMF and the importance of the flux ratio:
- Linda Arbuckle's Introduction to Glaze Calculation
- How Glazes Melt by Dave Finkelnburg
- Digitalfire's Understanding Glaze Calculation