Ball Clay

Highly Plastic Fine Particle Clay

Chemistry

CaO	0.300
K2O	0.900
MgO	0.300
Na2O	0.400
TiO2	1.000
Al2O3	25.000
SiO2	59.000
Fe2O3	1.000

Volatiles

LOI

12.000

Hazards

Ball Clay

Miscellaneous

Family: Ball Clay
Region: None
Mined At: Unspecified
Raw Mineral: No
Generic: Yes

Notes

There are hundreds of different ball clays available and they vary widely in plasticity, particle size, color, firing properties. A typical ball clay powder is light grey (from lignite) or cream color and fires to a buff or cream white color with some soluble salt deposits on the fired surface. They are typically unvitrified at cone 10. Ball clays are very plastic and much finer grained than kaolins. They are easily slaked in water when dry. Few people fully appreciate how 'sticky' and plastic it is until they mix some with water and work with it pure. Its fine particle size also makes it impermeable to the passage of water (a small test bar can take a very long time).

The term 'ball' traces to historic mining in England where large chunks of the clay were cut from the bank in ball shapes for transport to processing.

Ball clays are used in ceramic bodies (porcelains, stonewares and earthenwares, casting slips, pressing bodies) because of their plastic nature combined with high firing temperature. Ball clays have very high dry shrinkage combined with high green strength and slow drying. Were it not for the iron and coal impurities, ball clay would be an ideal ceramic material. However, in practical terms, it is used to achieve desired plasticity, but is minimized to reduce the detrimental effect it most often has on fired whiteness and drying properties.

A common starting recipe for a high temperature general purpose porcelain as is used in electrical porcelain or extruded pottery porcelain is 25% each of ball clay, kaolin, feldspar and silica. The ball clay:kaolin mix can be altered to change body plasticity without significantly affecting the maturing temperature.

In North America, most commercial ball clays are mined in the southeastern US. Ball clay deposits are common and were laid by the action of slow moving water with an acidity that tended to flocculate and settle the clay. It is common to find lignite associated with ball clay, and this accounts for the almost black appearance of many varieties when wet.

Ball clays tend to be quite refractory (PCE 28-34) and some dirtier deposits are sold as fireclays. Ball clay is not a clay mineral in itself, but contains other minerals, primarily kaolinite (but also montmorillonite, halloysite, and illite). Mica and quartz are also normally present in substantial amounts.

Ball clays vary widely in their plasticity, and it is difficult to compare them by quantitative tests because pure samples are difficult to mix and form and crack badly during drying. Thus, it is common to mix ball clay and flint 50:50 and prepare dry shrinkage, dry strength and fired strength bars for comparative testing. Another technique to produce a workable material is to calcine half of a sample to destroy its plasticity, then mix virgin:calcine 50:50. However most technicians find that flint dilution is advantageous for comparing color and solubles contents.

In general it may be said that English ball clays tend to have a higher dry strength (and thus drying shrinkage) than American ones, Kentucky ball clays have the lowest carbonaceous matter, English ones vitrify lower, Tennessee ones fire whitest.

Although some ball clays resist deflocculation because of hostile soluble impurities, most deflocculate very well with sodium silicate and other equivalent dispersants. A wide range of ball clay slurries and slips are used at all temperature ranges in casting processes. One common recipe uses a simple 50:50 ball clay:talc mix. This recipe and close derivatives are used in large quantities in the hobby casting market. The same mix is also dry pressed in the tile industry, and extruded for jiggering and wet processing in artware.

The refractories industry is a large user of ball clay. Common refractory materials lack plasticity and ball clay is used to help in forming and shape retention and to impart dry strength. The abrasives industry likewise uses it to bond aggregates until firing fuses the mass.

Engobes in the tile and brick industries are suspended, hardened, and adjusted to match body shrinkage by the addition of ball clay. Many pottery glazes contain ball clay to help suspend and harden them and control their shrinkage during drying (although some technicians prefer cleaner kaolins for this).

If the iron or lignite content of ball clay is a problem, it is common to employ bentonite to reduce the ball clay requirements (5% bentonite can provide as much improvement in plasticity and dry strength as 25% ball clay). However, care is recommended to make sure a fine grade of bentonite is used to avoid fired specks (bentonite also burns darker).

Unlike a kaolin, it is difficult to establish a generic or theoretical analysis, we have based this on a typical Kentucky ball clay in North America.

(Richard Willis)

Hydrous aluminosilicate earth with a typical empirical analysis averaging K₂O 1-3%, Na₂O 0.5-1.5%, CaO 1-4%, MgO 0.5-2%, Al₂O₃30-35%, SiO₂45-55%, TiO₂1-3%, Fe₂O₃ 1.5-3%, plus H₂O(n%) Name derived from original practice of cutting and rolling into balls for transport. Also called “blue clay” owing to varieties that are bluish in their natural, unfired, state. Nowadays ball-clay usually designates a natural, strong, highly elastic organic clay more suitable for hand-building, modeling, and throwing (and maturing at lower temperatures) than clays of purely kaolins and/or feldspars, though often blended with either or both. Popular ingredient for porcelain or other high-fire clay mixes, particularly in hand-building, sculpting, and wheel-throwing, and less so in casting slips. Good quality fires to a clean white. Frequently used in clay and glaze recipes where simply a “white clay” is called for to improve suspension in batch. A glacial sedimentary earth. Empirical analyses of two of the more popular ball clays yield: “Kentucky” = 49.9% SiO₂, 31.4% Al₂O₃, 0.6% Fe₂O₃, 1.5% TiO₂, 0.2% CaO, 0.3% MgO, 1.2% K₂O, 0.2% Na₂O, and 14.7% fire loss “Tennessee” = 50.3% SiO₂, 31.5% Al₂O₃, 0.6% Fe₂O₃, 1.3% TiO₂, 0.2% CaO, 0.3% MgO, 2.0% K₂O, 0.3% Na₂O, and 13.6% fire loss

Properties

Body Plasticity - All Bodies
Ball clay is the main plastic material used in clay bodies of all types. It is much more plastic than kaolin but also has much higher dry shrinkage and higher iron content. A typical white high temperature stoneware is often about 25% each of kaolin, ball clay, feldspar and silica.

Linked Articles

Dealing With Dust in Ceramics
A checklist of for changes and additions to your tools and equipment and suggestions for habit changes you need to make to control dust
DIOXINS in CLAYS by Edouard Bastarache
DIOXINS in CLAYS by Edouard Bastarache
Low Fire White Talc Casting Body Recipe
The classic white ball clay talc casting and modelling recipe has been used for many years. It is a dream to use as long as you are aware of the problems and risks.

Suppliers

Generic

Authors

Tony Hansen (Owner)

XML

<?xml version="1.0" encoding="UTF-8"?>
<material name="Ball Clay" descrip="Highly Plastic Fine Particle Clay" generic="1" rawmineral="0" searchkey="" loi="12.20">
<families>
<family name="Ball Clay"/>
</families>
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="" percent="0.300" tolerance=""/>
<oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="" percent="0.300" tolerance=""/>
<oxide symbol="K2O" name="Potassium Oxide" status="" percent="0.900" tolerance=""/>
<oxide symbol="Na2O" name="Sodium Oxide, Soda" status="" percent="0.400" tolerance=""/>
<oxide symbol="TiO2" name="Titanium Dioxide, Titania" status="" percent="1.000" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="25.000" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="59.000" tolerance=""/>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="1.000" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="12.000" tolerance=""/>
</volatiles>
<hazards>
<hazard name="Ball Clay"/>
</hazards>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>There are hundreds of different ball clays available and they vary widely in plasticity, particle size, color, firing properties. A typical ball clay powder is light grey (from lignite) or cream color and fires to a buff or cream white color with some soluble salt deposits on the fired surface. They are typically unvitrified at cone 10. Ball clays are very plastic and much finer grained than kaolins. They are easily slaked in water when dry. Few people fully appreciate how \'sticky\' and plastic it is until they mix some with water and work with it pure. Its fine particle size also makes it impermeable to the passage of water (a small test bar can take a very long time).

The term \'ball\' traces to historic mining in England where large chunks of the clay were cut from the bank in ball shapes for transport to processing.

Ball clays are used in ceramic bodies (porcelains, stonewares and earthenwares, casting slips, pressing bodies) because of their plastic nature combined with high firing temperature. Ball clays have very high dry shrinkage combined with high green strength and slow drying. Were it not for the iron and coal impurities, ball clay would be an ideal ceramic material. However, in practical terms, it is used to achieve desired plasticity, but is minimized to reduce the detrimental effect it most often has on fired whiteness and drying properties.

A common starting recipe for a high temperature general purpose porcelain as is used in electrical porcelain or extruded pottery porcelain is 25% each of ball clay, kaolin, feldspar and silica. The ball clay:kaolin mix can be altered to change body plasticity without significantly affecting the maturing temperature.

In North America, most commercial ball clays are mined in the southeastern US. Ball clay deposits are common and were laid by the action of slow moving water with an acidity that tended to flocculate and settle the clay. It is common to find lignite associated with ball clay, and this accounts for the almost black appearance of many varieties when wet.

Ball clays tend to be quite refractory (PCE 28-34) and some dirtier deposits are sold as fireclays. Ball clay is not a clay mineral in itself, but contains other minerals, primarily kaolinite (but also montmorillonite, halloysite, and illite). Mica and quartz are also normally present in substantial amounts.

Ball clays vary widely in their plasticity, and it is difficult to compare them by quantitative tests because pure samples are difficult to mix and form and crack badly during drying. Thus, it is common to mix ball clay and flint 50:50 and prepare dry shrinkage, dry strength and fired strength bars for comparative testing. Another technique to produce a workable material is to calcine half of a sample to destroy its plasticity, then mix virgin:calcine 50:50. However most technicians find that flint dilution is advantageous for comparing color and solubles contents.

In general it may be said that English ball clays tend to have a higher dry strength (and thus drying shrinkage) than American ones, Kentucky ball clays have the lowest carbonaceous matter, English ones vitrify lower, Tennessee ones fire whitest.

Although some ball clays resist deflocculation because of hostile soluble impurities, most deflocculate very well with sodium silicate and other equivalent dispersants. A wide range of ball clay slurries and slips are used at all temperature ranges in casting processes. One common recipe uses a simple 50:50 ball clay:talc mix. This recipe and close derivatives are used in large quantities in the hobby casting market. The same mix is also dry pressed in the tile industry, and extruded for jiggering and wet processing in artware.

The refractories industry is a large user of ball clay. Common refractory materials lack plasticity and ball clay is used to help in forming and shape retention and to impart dry strength. The abrasives industry likewise uses it to bond aggregates until firing fuses the mass.

Engobes in the tile and brick industries are suspended, hardened, and adjusted to match body shrinkage by the addition of ball clay. Many pottery glazes contain ball clay to help suspend and harden them and control their shrinkage during drying (although some technicians prefer cleaner kaolins for this).

If the iron or lignite content of ball clay is a problem, it is common to employ bentonite to reduce the ball clay requirements (5% bentonite can provide as much improvement in plasticity and dry strength as 25% ball clay). However, care is recommended to make sure a fine grade of bentonite is used to avoid fired specks (bentonite also burns darker).

Unlike a kaolin, it is difficult to establish a generic or theoretical analysis, we have based this on a typical Kentucky ball clay in North America.</note>
<note>Hydrous aluminosilicate earth with a typical empirical analysis averaging K2O 1-3%, Na2O 0.5-1.5%, CaO 1-4%, MgO 0.5-2%, Al2O3 30-35%, SiO2 45-55%, TiO2 1-3%, Fe2O3 1.5-3%, plus H2O(n%) Name derived from original practice of cutting and rolling into balls for transport. Also called “blue clay” owing to varieties that are bluish in their natural, unfired, state. Nowadays ball-clay usually designates a natural, strong, highly elastic organic clay more suitable for hand-building, modeling, and throwing (and maturing at lower temperatures) than clays of purely kaolins and/or feldspars, though often blended with either or both. Popular ingredient for porcelain or other high-fire clay mixes, particularly in hand-building, sculpting, and wheel-throwing, and less so in casting slips. Good quality fires to a clean white. Frequently used in clay and glaze recipes where simply a “white clay” is called for to improve suspension in batch. A glacial sedimentary earth. Empirical analyses of two of the more popular ball clays yield: “Kentucky” = 49.9% SiO2, 31.4% Al2O3, 0.6% Fe2O3, 1.5% TiO2, 0.2% CaO, 0.3% MgO, 1.2% K2O, 0.2% Na2O, and 14.7% fire loss “Tennessee” = 50.3% SiO2, 31.5% Al2O3, 0.6% Fe2O3, 1.3% TiO2, 0.2% CaO, 0.3% MgO, 2.0% K2O, 0.3% Na2O, and 13.6% fire loss</note>
</notes>
</material>

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