|Monthly Tech-Tip |
This is an example of cutlery marking in a cone 10 silky matte glaze lacking Al2O3, SiO2 and having too much MgO. Al2O3-deficient glazes often have high melt fluidity and run during firing, this freezes to a glass that lacks durability and hardness. But sufficient MgO levels can stabilize the melt and produce a glaze that appears stable but is not. Glazes need sufficient Al2O3 (and SiO2) to develop hardness and durability. Only after viewing the chemistry of this glaze did the cause for the marking become evident. This is an excellent demonstration of how imbalance in chemistry has real consequences. It is certainly possible to make a dolomite matte high temperature glaze that will not do this (G2571A is an example, it has lower MgO and higher Al2O3 and produces the same pleasant matte surface).
Predicting Glaze Durability by Chemistry in Insight-Live
How to spot out-of-balance indicators in the chemistry of ceramic glazes that suggest susceptibility to scratching or cutlery marking.
|Oxides||Al2O3 - Aluminum Oxide, Alumina|
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.
Glaze chemistry is the study of how the oxide chemistry of glazes relate to the way they fire. It accounts for color, surface, hardness, texture, melting temperature, thermal expansion, etc.
Where do I start in understanding glazes?
Break your addiction to online recipes that don't work or bottled expensive glazes. Learn why glazes fire as they do. Why each material is used. How to create perfect dipping and drying properties. Even some chemistry.