Glaze Tests 1 and Glaze Theory

We’ve started glaze testing in earnest now.  All the individual materials we normally use – and a few others such as toothpaste and emulsion paint – have been tested on red and grey clay, and the main groups identified – clays, glassformers, primary and secondary fluxes, stabalisers, colourants, opacifiers, frits.  We are now going to do line tests on pairs, then triaxial blends.

Oxidation top, reduction bottom

I’ve been ill for a few day so I thought I’d take the time to research glaze theory.  Phew! Who knew it was soooo complicated?

If you create two glazes with the identical chemical composition from two sets of different materials the results may be different.  This is because the molecules are bound in different ways in different materials, which can affect the way they react in the kiln. (Assuming you can find out the exact chemical composition of the materials and replicate identical kiln conditions).

On the other hand, potters have been making glazes from local materials for thousands of years without knowing anything about oxides, molecules, cones, pyrometers, electricity or gas. Gives me hope – just a little – that I might be able to mix something that’s not dry and turgid brown.

Glaze Simulator

I’ve tried a couple of my very own base glazes using Glaze Simulator to see what happens, and to see if the Simulator actually predicts the outcome accurately.


Amazed to see the difference between oxidation and reduction firing.  Apart from this, Glaze Simulator was reasonably accurate.  All should have fitted okay, but only 4 has no cracks on the ridges.


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