The body is Plainsman M390. These are commonly-used base glazes. The top one is an MgO matte, next down is a calcium matte. They react very differently to these additions. Notice also the difference when titanium dioxide is applied thickly. Tin oxide fires whiter than zircon (e.g. Zircopax). Each opacifier has issues. Tin is expensive. Titanium is difficult to mix into the slurry (screening required), not as white or opaque, variations in thickness produce more difference in results and it can turn blue. Zircon is more likely to cutlery mark, twice as much is required and it amplifies the color of any iron present.
This mug was thrown. But the handle was cast from L4005D, the recommended recipe for an M390-compatible casting body. This is not a product you can buy, you have to mix it yourself, but we have plenty of instructions and pictures. The fired maturity of the two (fired shrinkage and porosity) matches very well. The casting process is superior for certain shapes and ware types. And now, with 3D printing, it is much easier to make many kinds of casting molds. This handle mold is made by pouring plaster into a 3D printed form. These are strong, the handle on this glazeless mug endured a couple of good taps with a hammer and stayed solid. With glaze, the strength would be much better. The body fires a little browner in color than M390. It would be redder if we included more iron oxide in the recipe, but that would gel the slurry and make it harder to work with. As a red-burning body, this one has better casting properties than any other we have used.
Glaze opacity refers to the degree to which it is opaque. There is more than meets to eye to the subject of opacity control.
G1214Z - Cone 6 Silky Matte
This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte.
G2934Y - Cone 6 Magnesia Matte Low LOI Version
The same chemistry as the widely used G2934 but the MgO is sourced from a frit and talc instead of dolomite. It has a finer surface, less cutlery marking and staining.
G2934 - Matte Glaze Base for Cone 6
A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.