What phenomenon does a gradual appearance of defects in glazed ceramics often indicate?

The gradual appearance of defects in glazed ceramics often indicates the presence of thermal shock. This phenomenon occurs when there is a rapid change in temperature, causing the surface of the ceramic to expand or contract at a different rate than the underlying material. As a result, stresses can build up in the ceramic, leading to the formation of cracks or defects over time.

In the case of glazed ceramics, if the glaze and the body of the ceramic have different thermal expansion coefficients, the mismatch can lead to stress during cooling or heating cycles. This stress can result in visible defects appearing progressively as the material is subjected to repeated temperature fluctuations or inconsistent firing conditions. Understanding this mechanism is crucial for identifying and preventing defect formation in ceramic materials, particularly in applications where the integrity of the product is vital.