Pottery glaze is made up of five basic components. These components are silica, alumina, flux, colorants and modifiers. Even though all glazes are made up of the same components, there is a vast range of colors and types to choose from. The common ingredients that are in glaze colors are copper oxide, copper carbonate, cobalt oxide and iron oxide. When using glaze for your pottery products, it is always important to be aware of what exactly it is that you are working with. Below is a list of the five components that pottery glazes are made up with and what role they play.
Silica - When silica sand is heated in the kiln past 3100 degrees F it melts and forms into glass. Along with silica sand, flint is also added in this component for a proper finish.
Alumina - Alumina is used to help the glaze stick to the clay properly and keep it from running of the piece when heated up to high temperatures.
Flux - This component in particular is what helps melt the glass component called flint. The types of flux you can choose from are bone ash, iron, zinc, sodium and many more.
Colorants - Colorants are a whitening agent such as iron oxide, chromium oxide and talc.
Modifiers - Modifiers are used to change the glaze surface affects like the opacity and transparency. Below are the different types of modifiers
Opalescence - Reflects iridescent light on the glazed finish
Bentonite - Helps hold components into suspension during the firing process
Opacifiers - Gives glaze a white or opaque background. Types of opacifiers used are bone ash and tin oxide
Suspenders - Used to keep heavy components from setting out after the firing process
Gums - Used to toughen the glaze and help protect the finish before being fired at extremely high temperatures
In this video Chic Lotz discusses different glazing techniques:
Consider glazing bone china by preheating the china to allow the glaze to stick to the surface. Glazing machineries work light a giant car wash for ceramics.