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Glazes need a balance of the 3 main ingredients: Silica, Alumina and Flux.
* Too much flux causes a glaze to run, and tends to create variable texture on the surface. The texture may vary from shiny, where the glass is balanced, to matt where the excessive flux oxides may form visible, possibly lumpy, crystals.
* Too much silica will create a stiff, white and densely opaque glass with an uneven surface. It will be glossy in spots, but the suspended silica can form crystals producing harsh dry surfaces. Too much silica will also inhibit the melting of a glaze, and the resulting surface will be roughly textured like sandpaper.
* Too much alumina causes a glaze to stiffen and tend towards opacity, again with a textured surface where it is dry in spots. Glazes will often have pinhole defects. Too much alumina can inhibit the melting of the glaze to the extent that a poor quality matt glaze results, one that looks matt but is prone to discoloration.