Grog

Description

Crushed and pulverized fired clay pieces (biscuit) that are mixed with fresh clay to make it less plastic. Grog also makes the clay thicker, reduces shrinkage on drying and increases firing strength. Materials crushed to make grog can include broken and burned unglazed ceramic pieces, fire brick and saggers, but standard grog is made from refractory Fireclay that is relatively inert at most firing temperatures. Grog normally makes up 10% of the clay body and is graded according to its grain size; for example 30-60 means that the grains are smaller than a 30 mesh but larger than a 60 mesh.

In general, grog sizing corresponds to the following (Fournier, 1996)

• Passing 50 mesh = clay dust
• Passing 30 mesh = fine grog
• Passing 14 mesh = medium grog
• Passing 8 mesh = coarse grog

Grog that is too fine may make the clay absorb water too quickly. Grog that coarse or colored can be used for special effects.

Synonyms and Related Terms

grog (Ned.); chamota (Port.)

Resources and Citations

• R. Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Co., Radnor, PA, 1992, p. 137.
• R. Mayer, The Artist's Handbook of Materials and Techniques, Viking Press, New York, 1981
• Thomas Gregory, The Condensed Chemical Dictionary, Reinhold Publishing, New York, 3rd ed., 1942
• Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
• Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997