- Alkaline earth flux
- Has one of the highest melting points of all ceramic oxides
- 5072°F
- Starts fluxing action around 2138°F.
- forming eutectics with other oxides so it can melt at lower temps
- Melting action increases at higher temps
- Produces opaque matte surfaces, known as magnesium mattes, buttery mattes, or fat mattes
- Capacity to produce color is limited to pastel range
- can produce good clean white with tin oxide
- Used in recipes with cobalt, magnesium oxide tends towards lavender, while with copper color may blush pink.
- Glazes will give tea dust crystal effects and if magnesium matte glaze is slightly over-fired it will be characterized by floating bits of magnesium oxide in transparent glaze
- Very low expansion and contraction rate that may reduce crazing
- High surface tension and medium viscosity may cause pin holing or crawling, such as glaze called Sperry Mud Crack
- Has low toxicity
- Won’t volatilize at ceramic temps
- Some sources are slightly soluble in water (if acid is present)
- Insoluble sources are talc, dolomite, and magnesium carb or light magnesium carb (both are slightly soluble)
- Soluble sources are magnesium sulfate (Epsom Salts).