What could be a visible sign of manufacturing defects in clay shingles?

Efflorescence is a visible sign that often indicates a problem associated with clay shingles and their production process. It manifests as a white, powdery deposit on the surface of the shingles, caused by the migration of soluble salts that dissolve in moisture and then crystallize as the water evaporates. This can occur if the clay used in manufacturing contains high levels of soluble salts or if there was inadequate drying during the production process, leading to moisture retention.

While physical cracks, color variation, and thickness inconsistency may also suggest potential issues with clay shingles, they do not specifically signal defects resulting from the manufacturing process in the same way that efflorescence does. Physical cracks might stem from environmental factors or stress, color variation could occur from variances in firing temperatures or clay batches, and thickness inconsistency might relate more to handling or installation than to underlying manufacturing defects. In summary, efflorescence directly relates to the composition and conditions of the clay during production, making it a clear indicator of a manufacturing defect.