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Identifying Glaze Mechanisms

Section: Glazes, Subsection: Introduction

Description

If you can look at a glaze recipe and pick out the materials add to produce the color, opacity and variegation you can transplant these into your own base glaze

Article

The traffic in glaze recipes is having a net negative effect on functional ceramics in education, hobby, and industry. It is fostering a culture that runs counter to the idea of understanding and controlling our materials and recipes, it breeds ignorance of oxide and material sciences and the true nature of the ceramic process. Weak, leachable, difficult-to-clean, crazed, shivered, and leaching glazes hurt the reputation of the pottery and ceramic industry.

We recommend a 'base glaze with variations' model. When a base glaze is well understood it can be improved over a period of years. When it is improved, variations based benefit also. Imagine a base that is nice to use and apply; never cracks on drying; does not settle out; is reliable; cost effective; resistant to leaching, crazing, and cutlery marking; is gloss and temperature adjustable; and is easily opacified, colored, and variegated, etc. This is not dreamland, it is possible, but only if you focus on one good base glaze. Would it not make good sense to transplant the 'mechanisms' from new glaze recipes into your base rather than bring new recipes with their new materials and problems into your studio?

The 'Mechanism' of a glaze is the particular material(s) or process(es) that make it do the special thing it does. For example, consider a glossy blue. Such a glaze is simply a glossy base with added cobalt. If you already have a glossy glaze that fits your clay, applies well, is hard and nonleaching, etc. then why not put the cobalt into it instead of introducing a new unproven transparent glaze into your operation?

Consider another kind of mechanism. A glaze recipe might fire matte because:

-It has a high alumina and low silica ratio and the alumina stiffens the melt so that the microsurface is rippled.
-It is not being fired high enough to melt properly.
-It is covered with a fine mesh of crystals that grow during cooling.

Knowing this will give you direction if you need to adjust. For example, to make an underfired matte glossier you add feldspar, to make an alumina matte glossier you add silica, to make a crystal matte glossier you cool more quickly or increase kaolin to stiffen the melt and impede crystal growth.

Consider a complex mechanism: A copper red glaze is a little copper and tin in a low alumina fluid glaze fired in reduction on a low iron body. Within this system you can introduce a little boron to move the color toward purple. Knowing this will go a long way to troubleshooting or moving the mechanism into another more suitable recipe.

In the past we have tended to mix recipes from others or textbooks without regard to the 'mechanism' at play in recipes and firing. A little understanding is one secret to seeing recipes differently, getting better control, and keeping the number of glaze recipes in your studio to a minimum.

Links to Other Items

R-42

Authors

Tony Hansen (Owner)

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