During the firing process the glaze and the clay ideally become connected inseparable. To let this happen, it is required to match the physical properties of the glaze to the clay body. It must be good applicable and may not be wiped off easily. The melting temperature must be below but close to the sintering temperature of the clay body but the glaze may neither cook nor run off. During the cooling process the shrinkage of the glaze should be identical to that of the clay to avoid tension cracks and flaking. As every clay has a different coefficient of extension, commercially available glazes are always defined for an average value and need to be adjusted. However, commercial glaze vendors do normally not publish their recipes, which makes an adjustment difficult.For this reason, I started to develop my own glazes. Starting with recipes from literature I create a first version of the recipe with a glaze calculator. As soon as the theoretical coefficient of extension and the melting temperature are in the desired range I start to fine-tune the recipe experimentally. Using a blending triangle, I systematically vary the three most influencing components in 66 glaze samples. As soon as the composition is optimal, I start a second experimental row with the coloring components. Eventually a third experiment is necessary to determine deviations under different conditions, e.g. firing in a capsule might change the resulting glaze colors.
A special area of development are experiments, where glazes shall show some craquelure. Here the coefficient of extension is deliberately moved away from the optimum but may not influence the glaze fit on the clay body.
This is the story of a glaze development with the exclusive usage of stones from the Baltic sea shore.
Where has a potter the best possibility to use his own products? Exactly, in his kitchen.