WHAT IS BALL CLAY?
Ball clay is one of the most popular ceramic materials. It also has many applications in industrial ceramics. This is because they are plastic in nature and fine-grained.
Its name comes from the extraction method used in mining, which consisted and consists of separating it into spherical shapes, actually into balls of clay.
It is a material with a high percentage of kaolinite, just like kaolin, in fact some say that they are not different clays, taking into account the minerals of which they are composed. It is generally darker, as it can be found with a color ranging from dark brown to even black, due to its formation process.
As for the color, it should be noted that after firing it can become lighter in color and even white.
It is a clay very appreciated in ceramics for its resistance.
How is ball clay made?
It is a material of natural origin, the only artificial aspect is its shape when extracted. This fine-grained clay is formed, like most, by sedimentation. In this process, the kaolinite, due to its interaction with water, mixes with mica and quartz, as well as with a large amount of organic components. This is what produces the color we mentioned before.
Once extracted, it is usually left to air dry for a period of time and can then be treated. It is usually packed in big bags, generally of about 50 kg (it must be taken into account that this type of material has a great industrial application).
It varies in its “chemical formula” depending on its sedimentary formation, but mainly the materials from which ball clay is made are: kaolinite (20% to 80%), quartz (5%-60%) and mica (10%-25%).
In addition, it can have different components included during its creation, the most remarkable is the presence of organic material that gives it certain characteristic properties that we detail below. In addition, being a sedimentary clay, it contains lignite.
PROPERTIES OF BALL CLAY
- It has a pH between 6 and 8 (to translate a little to those who have stayed the same, it is more or less in the middle on the scale that measures the acidity or alkalinity and ranging from 0 to 14, to give you an idea, its pH would be between milk and seawater, more alkaline the latter).
- It takes longer to dry than kaolin and has a higher plasticity and dry strength compared to kaolin.
- This is due to its organic matter content, which also gives it its darker, brownish color, although once cooked, the ball clay takes on a lighter color.
- In the drying process there will be a certain shrinkage (between 15% and 25%), due to which cracks may appear, this must also be taken into account in the case of engobes or glazes.
- Once cooked, it has a water absorption capacity of 10%.
- The presence of lignite in the chemical composition of ball clay, in addition to increasing its strength, increases its porosity after firing.
The uses of ball clay, due to its properties, are centered on industry.
- Due to its resistance (both in transport and in use), it is used in the manufacture of medical devices.
- As floor and wall coverings.
- Manufacture of refractory material.
- As an electrical insulator.
- As a binder in paints.
- In fertilizers.
Uses of Ball Clay in ceramics:
It is used to modify the properties of purer kaolins, for example to give them plasticity.
It is also used in high temperature engobes.
It is incorporated into darker earths to achieve a whiter toned clay.
And, of course, to create tableware, as it gives them strength.
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© Image 2: BBC MInes India Private Limited
© Image 3: Modkha