About High Plasticity Ball Clay
High plasticity ball clay is selected for very fine particle size and strong binding power. A large share of its particles is below 2 µm, giving a high water of plasticity and a dry modulus of rupture well above that of ordinary ceramic clays. Those properties matter most in sanitaryware, where large, complex pieces such as WC pans, wash basins and cisterns are slip cast and must survive demoulding, fettling and drying without cracking.
In a vitreous china body, ball clay typically sits alongside kaolin, feldspar and quartz. The high plasticity grade supplies most of the green and dry strength, and it also influences casting rate, wall thickness consistency and slip thixotropy. A clay that casts too slowly reduces mould output; one that sets up too quickly leaves soft spots or drain lines. This grade is selected and blended to give a workable balance, with deflocculant demand checked as part of routine quality control.
Obsidian Minerals tests the grade for dry strength, residue, chemistry and fired properties, and can supply it as dry powder, noodles or filter cake to suit the customer's slip house. Casting trials with the customer's own body recipe are recommended before changing clay source, and samples are available for that purpose.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| SiO₂ | 48–56 % | XRF (internal method) |
| Al₂O₃ | 27–32 % | XRF (internal method) |
| Fe₂O₃ | ≤ 1.5 % | XRF (internal method) |
| TiO₂ | ≤ 1.5 % | XRF (internal method) |
| Loss on ignition | 10–14 % | Internal method (1,000 °C) |
| Dry modulus of rupture | ≥ 3.0 MPa | ASTM C689 |
| Particles < 2 µm | ≥ 70 % | Internal method (sedimentation) |
| Residue on 45 µm (325 mesh) | ≤ 2.0 % | ASTM C325 |
Typical values for guidance. Guaranteed limits, including dry strength and fired properties, are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
High dry strength
A typical dry modulus of rupture of 3.0 MPa or more helps large sanitaryware castings withstand demoulding, fettling, handling and drying with fewer cracks and breakages.
Very fine particle size
With most particles below 2 µm, the clay develops strong plasticity and bonding power, so a moderate addition binds the non-plastic feldspar and quartz in the body effectively.
Balanced casting behaviour
The grade is blended to give a practical casting rate and stable slip thixotropy, helping maintain mould turnover and consistent wall thickness across large and complex pieces.
Controlled coarse residue
Residue on 45 µm is typically 2 % or less, which limits surface pinholes, specks and weak points in cast ware and reduces the load on slip sieves.
Flexible supply forms
Available as dry powder, noodles or filter cake, so slip houses can choose the form that suits their blunging equipment, dust control and storage arrangements.
Applications
Sanitaryware slip casting
The principal plastic component in vitreous china bodies for WC pans, wash basins, cisterns and pedestals, providing the green and dry strength needed for large cast pieces.
Electrical porcelain
Used in extruded and turned bodies for insulators and electrical porcelain, where high plasticity helps forming and strong dry bodies reduce handling losses before firing.
Glaze and engobe suspension
Small additions keep glaze and engobe slurries in suspension, improve adhesion of the raw glaze layer to the ware and help reduce crawling during firing.
Plastic forming bodies
Suited to jiggered, roller-formed and extruded tableware and stoneware bodies, where the clay's plasticity improves forming behaviour, helps surface finish and limits cracking during drying.
Usage & handling
- Sanitaryware bodies commonly contain about 20–35 % ball clay, balanced against kaolin for strength and casting rate.
- Blunge with a deflocculant system such as sodium silicate and soda ash, and run a deflocculation curve on each new lot.
- Age the slip and check specific gravity, fluidity and thixotropy before casting.
- Store under cover; protect noodles and filter cake from drying out and from contamination.
Packaging & supply
- Dry powder in 25 kg or 50 kg HDPE or paper bags
- 1 MT and 1.2 MT jumbo bags for powder, noodle or filter cake forms
- Custom packing arrangements on request
Frequently asked questions
Why is high plasticity ball clay used in sanitaryware?
Sanitaryware pieces are large and complex, and they are cast as soft, wet shapes that must be demoulded, fettled and dried without damage. High plasticity ball clay gives the body the green and dry strength to survive these steps. It also shapes casting rate and slip behaviour, which affect mould output and wall consistency.
What dry strength does this grade have?
The typical dry modulus of rupture is 3.0 MPa or higher, measured on dried test bars to ASTM C689. Actual strength in a body depends on the proportion of ball clay, the other raw materials and the forming method. The guaranteed minimum for your order is stated on the Technical Data Sheet and reported on the batch CoA.
How does ball clay affect casting rate?
Very fine, highly plastic clays form a dense cast layer that slows the passage of water into the mould, so they tend to reduce casting rate. Coarser clays cast faster but give weaker ware. Sanitaryware makers balance the two by adjusting the ball clay to kaolin ratio and the deflocculant level. This grade is blended to sit within a practical range.
Which deflocculant should be used with this clay?
Sodium silicate, often combined with soda ash, is the most common deflocculant system for sanitaryware slips, and some plants also use polymer dispersants. The optimum dose depends on the clay's soluble salts and organic content, which vary slightly between lots. A deflocculation curve on each new lot is the most reliable way to set the dose.
Is the fired colour of this grade white?
It typically fires to a light cream or ivory colour, which is fully acceptable under a sanitaryware glaze. The grade is optimised for strength and casting behaviour rather than maximum whiteness. Where an unglazed or very white body is required, the high whiteness grade or a blend with white-firing kaolin should be considered.