Natural clays are readily found in the earth and have the quality of being malleable by hand when wet and becoming firm and hard when dried. The heating or firing of clay imparts further strength, and exposure to high temperatures causes vitrification between the clay particles making the material water impervious. The vitification process is visually important on the surface of the object where glass layers or glazes are formed by chemical reaction of the clay bodies, added topical mineral slurries and the interior firing atmosphere.
Ceramic objects are susceptible to cracks, breaks, and glaze loss, especially for outdoor objects. Sun baked and low fire ceramics are particularly susceptible to damage due to low strength and high water absorption rates. Conservation requires investigation and treatment compatibility with the material types, object design and function, as well as past and future display conditions. Interior reinforcement and anchoring systems are typically required for architectural elements and outdoor sculpture.