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. There are hundreds of different ball clays available. Potentially they should vary widely in plasticity, particle size, raw color, and drying properties. But in practice, most are remarkably similar. A typical ball clay powder is light grey (from lignite) or cream color and fires to a buff or cream (with some soluble salt deposits on the fired surface). Ball clays tend to be quite refractory (PCE 28-34) and some less processed 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 present in substantial amounts (e.g. 10-20% for Tennessee ball clays).

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 these materials are until they mix some with water and work with it pure. The fine particle size also makes them impermeable to the passage of water (a small test bar can take a very long time to dry).

While potters only buy ball clay as a powder, industrial users have access to the material in many forms (shredded, noodled and partially deflocculated, chopped filter press cake, vacuum pugged extrusion, crumble with about 10% moisture). These forms enable a more consistent supply and alot of flexibility, especially when making casting slips (since ball clays are the most difficult to disperse materials in the bodies).

They are typically unvitrified at cone 10. There are a wide range of ball clays used in traditional ceramic manufacture in North American and they have surprisingly similar firing characteristics (maturity and color). In one test we made 50:50 ball clay:feldspar mixes of 8 different common ball clays (from a range of suppliers), from cone 6 to 10 all had the same porosity and fired appearance.

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 their iron and coal impurities, ball clays would be ideal ceramic materials. However, in practical terms, they are employed to achieve desired plasticity, but are minimized to reduce the detrimental effect 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 grey appearance of many varieties (when wet).

It is difficult to compare their plasticities by quantitative tests because pure samples are difficult to mix and form (they are incredibly sticky) and crack badly during drying. Thus, it is common to mix ball clay and silica 50:50 and compare dry shrinkage, dry strength, soluble salts, fired color. Another technique to mix raw:calcine 50:50. In our testing of many ball clays, drying shrinkage and water of plasticity it very similar (those intended for casting have a little lower drying shrinkage, but they also fire very similar). 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 in casting at all temperature ranges. One common recipe uses a simple 50:50 ball clay:talc mix (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, claiming they gel the slurry better and prevent drip-drip during drying). It makes a big difference what ball clays are used, some produce a syrupy mess that settles while others produce a beautifully suspended creamy slurry. In North America, Old Hickory #5 and Old Hickory No. 1 Glaze ball clays work well in glazes. 10-15% ball clay should be enough to suspend a glaze, if there is any less add 1-2% bentonite. Recipes with 20% or more ball clay risk shrinking and cracking during drying.

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 provided one for a typical Kentucky ball clay.

If you use ball clay in your production there is good reason to be doing routine quality control to make sure it is remaining consistent. Ball clays are likely the most variable material you will have to deal with. They can sometimes have particulate impurities (especially lignite) and exhibit differences in soluble salts content, drying shrinkage, drying performance, fired maturity, fired color and behavior in slurries. Consider the SHAB test (see link below).

Adequate quartz content is an important factor in porcelain and whiteware bodies (it is an important structural element in the fired matrix and it is needed to prevent glaze crazing). Since ball clays contain quartz, it is possible to use less raw silica (quartz) powder in the recipe if ball clay percentages are high. Of course, the quartz grains in the ball clay are finer, so they will dissolve into the feldspar glass more readily.

Ball Clay

S
oil may be considered the most mundane material in nature, but it has
unexpectedly changed the forms, thanks to the ingenuity of humans.
People started their manipulation of soil as early as the Neolithic Age,
although it was defined as neither ceramics nor pottery at that time. In that
natural environment, people chose soil, water, sand, stone, and other kinds
of mineral substances as materials, and then started, with the application
of exquisite workmanship, to adorn their creations with rich patterns and
embrace a painted-pottery culture. Both the Banpo and the Miaodigou
ceramics are abundant in pattern with moving arcs crossing on the surface
and vivid figures of plants and animals, illustrating the intimate connections
with human life brought forth by these primitive materials.

Natural materials from the earth have perpetually pursued their identity
in human history in the East and the West, the ancient and the modern.
Celadon emerged during the late Eastern Han Dynasty, when people used
the "dragon kiln" to increase the temperature of the kiln and made porcelain
with kaolin clay (white clay). During the Northern Dynasties, a profoundlyinfluential pottery named "white porcelain" emerged. After the Eastern Han
Dynasty, porcelain technology developed rapidly and matured until the Tang
Dynasty. In the Song Dynasty, its elegant and dignified quality, paired with
beautiful shapes, further elevated the form. Apart from the popularity of
decorative porcelain in the Yuan Dynasty, there were also classical works
distinguishable by their blue-and-white patterns or by an underglaze of red.
Porcelain technology later developed continuously in the Ming and the Qing
Dynasty, and the diversity of cultural aesthetics endowed humanity with
various patterns and style of porcelain.
In the meantime, Western ceramics also developed substantially from the
18th to the 19th century. Delicate porcelain, tea sets, and handicrafts created
during the Baroque and Rococo periods in Europe were not only symbols of
identity and status, but also the imprint of the era's aesthetic. In the British
Arts and Crafts Movement at the end of the 19th century, people yearned for
the natural and handmade that brought them to a new understanding about
materials. People began to realize that handmade goods retain the mark
of labor, which marks the collaboration of nature and humans. In a newly
modern society that emphasized efficiency and mechanized production,
a regression to raw materials and crafts enabled people to consider the
relationship of humans and nature. In this iteration, thanks to human
ingenuity, porcelain moved far from its original form as a natural material, and
became closely associated with the history, culture and aesthetics of diverse
nationalities.