Glossary of Industry Terms




That degree of vitrification evidenced visually by complete resistance to dye penetration. (ASTM C 242).  NOTE: The term impervious generally signifies zero absorption, except for floor and wall tile which are considered “impervious” up to 0.5 per cent water absorption.

Impervious tile

Has water absorption of 0.5 percent or less.


Decorated by cutting or indenting the ware surface. (ASTM C 242).

inglaze decoration

See Decoration, inglaze.

Initial setting time

The time required for a freshly mixed cement paste, mortar or concrete to achieve initial set. (See also Final setting time.)

Ironstone ware

(Stone china, white granite ware). Historic terms for a durable English earthenware. (ASTM C 242).

Isolation joint

A separation between adjoining parts of a concrete structure, usually a vertical plane, at a designed location such as to interfere least with performance of the structure, yet such as to allow relative movement and avoid formation of cracks elsewhere in the concrete and through which all or part of the bonded reinforcement is interrupted. (See also Contraction joint.)