Underkilned

Underkilned is a term used in ceramics and pottery to describe pieces that have not reached the full maturation temperature required for the clay body and glaze to become fully vitrified. The expression is less common than underfired or underfiring, but it appears in some studio notes, catalogs, and discussions about firing practices. It arises when a firing cycle stops short of the target temperature, or when interruptions such as power outages or equipment faults prevent the kiln from completing a proper cycle.

Etymology and scope: The word combines under- with kiln, indicating insufficient heat treatment. It is typically used to refer to a ceramic piece that is partially fired, as opposed to a correctly fired work that has reached the intended maturity. The concept overlaps with underfired, bisque, and glaze firings, but underkilned emphasizes the incomplete maturation aspect.

Characteristics and effects: Underkilned pieces generally show higher porosity and a rough or chalky texture due to incomplete vitrification. Color and glaze development may be uneven or muted, and mechanical strength is reduced, making the ware more prone to damage if stressed. Some glazes may not bond evenly, leading to pinholes or chipping. Re-firing a piece that has been underkilned can restore maturity if the glaze and clay can withstand additional heat, though care must be taken to manage thermal shock and glaze behavior.

Causes and context: Causes include inadequate kiln calibration, firing heavy or thick-walled wares, early termination of the firing cycle, or intentional artistic choice to achieve a porous surface. In some studios, underkilned wares are labeled or shelved as a distinct category for study or textural effect.

See also: bisque firing, glaze firing, firing schedule, vitrification.