Grog (clay)
Encyclopedia
Grog, also known as firesand and chamotte, is a ceramic
raw material. It has high percentage of silica and alumina. It can be produced by firing selected fire clay
s to high temperature before grinding and screening to specific particle sizes. It can also be produced 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. It is available as a powder, mortar
, or in the form of fire brick
s.
(Fe2O3), and 2% maximum of calcium oxide
(CaO) and magnesium oxide
(MgO) combined.
Its melting point is approximately 1780 °C (3,236 °F). Its water absorption
is 7% maximum. 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 also not easily wetted by steel
.
and sculpture
to add a gritty, rustic texture called "tooth"; it also reduces shrinkage and aids even drying. This prevents defects such as cracking, crow feet patterning, and lamination. The coarse particles open the green clay body to allow gases to escape. It also adds structural strength to hand-built and thrown pottery during shaping although it can diminish fired strength.
The finer the grog particles are, the closer the clay bond, and the denser and stronger the resulting 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. "
Other uses for grog is processing ZnO Metal Oxide Varistor
(MOV). It is put at the base of the "blocks" on the topside of the bottom of a refractory sagger to keep the blocks from sticking to the sagger. This is because ZnO MOV has a polymer binder that upon drying acts as a glue. The grog at the base prevents gluing and acts as a vent for carbon gases while drying and sintering. The grog is a gritty form of ZnO to prevent contamination.
to unfired clay. Several pottery types from the European Bronze Age
are typologised
on the basis of their grog inclusions.
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
raw material. It has high percentage of silica and alumina. It can be produced by firing selected fire clay
Fire clay
Fire clay is a term applied to a range of refractory clays used in the manufacture of ceramics, especially fire brick.High grade fire clays can withstand temperatures of 1775°C , but to be referred to as a "fire clay" the material must withstand a minimum temperature of 1515°C...
s to high temperature before grinding and screening to specific particle sizes. It can also be produced from pitchers
Pitchers (ceramic material)
Pitchers are pottery that has been broken in the course of manufacture. Biscuit pitchers are crushed, ground and re-used, either as a low-percentage addition to the virgin raw materials on the same factory or elsewhere. The crushed material is also used in other industries as an inert filler....
. The particle size distribution
Particle size distribution
The particle-size distribution of a powder, or granular material, or particles dispersed in fluid, is a list of values or a mathematical function that defines the relative amounts of particles present, sorted according to size...
is generally coarser in size than the other raw materials used to prepare clay bodies. It tends to be porous and have low density. It is available as a powder, mortar
Mortar (masonry)
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
, or in the form of fire brick
Fire brick
A fire brick, firebrick, or refractory brick is a block of refractory ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency...
s.
Properties
Grog is composed of: 40% minimum alumina (Al2O3), 30% minimum silica (SiO2), 4% maximum Iron(III) oxideIron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...
(Fe2O3), and 2% maximum of calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
(CaO) and magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
(MgO) combined.
Its melting point is approximately 1780 °C (3,236 °F). Its water absorption
Water absorption
During the transmission of electromagnetic radiation through a medium containing water molecules, portions of the electromagnetic spectrum are absorbed by water molecules...
is 7% maximum. Its thermal expansion coefficient is 5.2 mm/m and thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
is 0,8 W/(m·K) at 100°C and 1,0 W/(m·K) at 1000°C. It is also not easily wetted by steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
.
Applications
Grog is used in potteryPottery
Pottery is the material from which the potteryware is made, of which major types include earthenware, stoneware and porcelain. The place where such wares are made is also called a pottery . Pottery also refers to the art or craft of the potter or the manufacture of pottery...
and sculpture
Sculpture
Sculpture is three-dimensional artwork created by shaping or combining hard materials—typically stone such as marble—or metal, glass, or wood. Softer materials can also be used, such as clay, textiles, plastics, polymers and softer metals...
to add a gritty, rustic texture called "tooth"; it also reduces shrinkage and aids even drying. This prevents defects such as cracking, crow feet patterning, and lamination. The coarse particles open the green clay body to allow gases to escape. It also adds structural strength to hand-built and thrown pottery during shaping although it can diminish fired strength.
The finer the grog particles are, the closer the clay bond, and the denser and stronger the resulting 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. "
Other uses for grog is processing ZnO Metal Oxide Varistor
Varistor
A varistor is an electronic component with a "diode-like" nonlinear current–voltage characteristic. The name is a portmanteau of variable resistor...
(MOV). It is put at the base of the "blocks" on the topside of the bottom of a refractory sagger to keep the blocks from sticking to the sagger. This is because ZnO MOV has a polymer binder that upon drying acts as a glue. The grog at the base prevents gluing and acts as a vent for carbon gases while drying and sintering. The grog is a gritty form of ZnO to prevent contamination.
In archaeology
In archaeological terminology, 'grog' is crushed fired pottery of any type that is added as a temperTemper
Temperare is the Latin origin of words like "temperature" and "tempering"; it and "tempo" come, in turn, from tempus...
to unfired clay. Several pottery types from the European Bronze Age
Bronze Age
The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...
are typologised
Typology (archaeology)
In archaeology a typology is the result of the classification of things according to their characteristics. The products of the classification, i.e. the classes are also called types. Most archaeological typologies organize artifacts into types, but typologies of houses or roads belonging to a...
on the basis of their grog inclusions.