Glaze opacity refers to the degree to which it is opaque. There is more than meets to eye to the subject of opacity control.
Ceramic glazes that mark from cutlery are either not properly melted (lack flux), melted too much (lacking SiO2 and Al2O3), or have a micro-abrasive surface that abrades metal from cutlery.
|Recipes||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.
|Oxides||ZrO2 - Zirconium Dioxide|