Calcium Oxide and Magnesium Oxide

I've run two raku glaze bases, known to have problems with chromium-tin mason stains, through my glaze calculator software.

Louden's Base contains 22.8% calcium oxide, and 3.79% magnesium oxide.

A base used by Rebecca Johnson, of Buck, Snort and Run Clayworks, contains 24% calcium oxide, and 4.17% magnesium oxide.

According to the Masoncolor site, the chromium-tin mason stains should contain between 6.7 and 8.4 percent calcium oxide, and be free of zinc oxide and magnesium oxide.