Controlling glazes – Avoiding hair cracks and chips

»1 Dilatometer curves for brick, quartz glass and two glazes

»2 Hair cracks

»3 Chip

»4 Stress measurement on a test bar

»5 Stress curves

»6 Shrinkage curves starting at 700° C and coupling temperature

Glaze and body must always bond to one another to prevent creation of hair cracks in the glaze, or to prevent pieces of glaze from chipping off the underlying body. The article shows which aspects play a role in this bonding process and which laboratory measuring methods prior to production lead to the best insight about possible risks.

1 Introduction

A glaze is a thin glassy layer bonded to ceramic in the firing process, with the objective to obtain certain aesthetic properties, improve the sustainability of the object it is applied to, obtain a smooth surface and/or make it waterproof. Glazes can be transparent or opaque, matt or glossy, and there are many colours.

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1 Problem description In the late 1990s, an incident was reported in the roofing tile industry in which a large number of around one- to two-year-old glazed roofing tiles had become discoloured, as...

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Causes and avoidance of firing-related damage Part 2: Strength-reducing reactions in the heating-up zone from 500 to 800° C

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