Grog
Definition
Crushed fragments of previously fired ceramic mixed into new clay as temper; recognisable in thin section by their fired-clay texture, which differs from the surrounding unfired or freshly fired matrix.
- Composition
- Crushed fragments of previously fired ceramic
- Use
- Added as temper to new clay
- Identification method
- Thin-section petrography
- Distinguishing feature
- Fired-clay texture against unfired matrix
Common questions
Why would a potter add grog rather than a mineral temper like sand or shell?+
Grog reduces shrinkage and cracking during drying and firing because it is already fired and dimensionally stable, and because it is made from clay itself it bonds well with the surrounding fresh clay body, properties that mineral tempers do not offer in the same way.
How does identifying grog help source or date a ceramic exhibit?+
The grog's own fabric, composition, and inclusions can be examined separately from the surrounding matrix under thin section, and because it represents an even older, previously fired ceramic tradition, its characteristics can point to a manufacturing region or period distinct from that of the vessel it was used to temper.
Related terms
- Ceramic Fabric
- The combination of clay matrix and included particles (temper, natural inclusions, and voids) that makes up a fired ceramic; the raw material...
- Dehydroxylation
- The loss of structural hydroxyl groups from clay minerals (principally kaolinite) between about 450 and 600 °C during firing; an irreversible reaction...
- Mullite
- An aluminosilicate phase (3Al2O3·2SiO2) that nucleates in fired clay above roughly 980 °C, coinciding with the characteristic exothermic reaction of the kaolinite-to-mullite...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...
- Temper
- Material deliberately added to clay before forming to reduce drying shrinkage and firing cracking; common temper types include sand, grog (crushed old...