Grog (clay)

Grog, also known as firesand and chamotte, is a raw material for making ceramics. It has a high percentage of silica and alumina.

It is normally available as a powder or chippings, and is an important ingredient in Coade stone.

ProductionEdit

It can be produced by firing selected fire clays to high temperature before grinding and screening to specific particle sizes. Another method makes it from pitchers. The particle size distribution is generally coarser in size than the other raw materials used to prepare clay bodies. It tends to be porous and have low density.

PropertiesEdit

Grog is composed of 40% minimum alumina, 30% minimum silica, 4% maximum iron(III) oxide, up to 2% calcium oxide and magnesium oxide combined.[1]

Its melting point is approximately 1,780 °C (3,240 °F). Its boiling point is over 9,000 °C (16,230 °F). Its water absorption is maximum 7%. Its thermal expansion coefficient is 5.2 mm/m and thermal conductivity is 0.8 W/(m·K) at 100 °C and 1.0 W/(m·K) at 1000 °C. It is not easily wetted by steel.[1]

ApplicationsEdit

Grog is used in pottery and sculpture to add a gritty, rustic texture called "tooth"; it reduces shrinkage and aids even drying. This prevents defects such as cracking, crows feet patterning, and lamination. The coarse particles open the green clay body to allow gases to escape. Grog adds structural strength to hand-built and thrown pottery during shaping, although it can diminish fired strength.

The finer the particles, the closer the clay bond, and the denser and stronger the fired product. "The strength in the dry state increases with grog down as fine as that passing the 100-mesh sieve, but decreases with material passing the 200-mesh sieve." [2]

In Middle and South Europe, grog is used to create fire-resistant chamotte type bricks and mortar for construction of fireplaces, old-style and industrial furnaces, and as component of high temperature application sealants and adhesives.

ArchaeologyEdit

In archaeology, 'grog' is crushed fired pottery of any type that is added as a temper to unfired clay. Several pottery types from the European Bronze Age are typologised on the basis of their grog inclusions.

See alsoEdit

ReferencesEdit

  1. ^ a b Jain 2003, p. 82.
  2. ^ Liddell 1922, p. 503 .
  • Jain, P. L. (2003), Principles of Foundry Technology (4th, revised ed.), Tata McGraw-Hill, ISBN 978-0-07-044760-8.
  • Lidell, Macy Liddell (1922), Handbook of chemical engineering, Volume 1 (unknown, revised ed.), McGraw-Hill Book Company, ASIN B000UFRYQI.