Brand : REFSAN
Price : 17,57TL


MgO is best known for its ability to matte glazes in larger proportions. The mechanism of this is different at higher temperatures (vs. low). At medium and high temperatures it is sourced mainly from dolomite and talc, as the proportion of MgO is increased (against other fluxes) the viscosity (and surface tension) of the melt increases and the glaze produced is more matte. As proportions rise even further (e.g. above 0.4 molar) the glaze becomes more opaque (as a product of incomplete glass development). For this reason, MgO is one of the most effective matting agents. For example, glazes having almost no alumina, very slow silica and very high boron that would otherwise run right off the ware can be completely stabilized with an MgO content of 0.3-0.4 molar. Unlike a refractory stabilizer, in many formulations MgO does not significantly impede melting and glass development when it mattes the glaze. At lower temperatures the matting mechanism of MgO is that it simply stiffens and opacifies the glaze due to its refractory nature. It is common to source it from magnesium carbonate in these ranges. Like CaO, MgO it is very refractory by itself, around 2800C melting point!

-Since the surface tension of MgO-containing melts does increase with its proportion, this can cause crawling if the glaze laydown has any shrinkage issues. This is less of a problem in reduction and most problematic in low fire.

-MgO is very valuable for its lowering effect on glaze thermal expansion (this is one reason why MgO mattes can be made very resistant to crazing). Low expansion frits are invariably based on MgO. Theoretically, surface character is best maintained when introducing MgO into a glaze to replace calcia, baria, and zinc. Still, replacing the alkalis with MgO is the single most effective strategy to reduce crazing, this works so well because oxide molecules of the highest possible expansion are being replaced with ones of the lowest. But this must be done with caution since having more than about 0.1 molar will begin to affect gloss. Also, you will have to determine if color is detrimentally affected. Yet many liner glazes have plenty of gloss and color is not an often an issue, they are excellent candidates for MgO strategies to deal with crazing issues.