The first examples of stoneware date back to China’s Shang Dynasty, two millennia BCE. The name stoneware does a superb job of suggesting the qualities of this gritty ceramic. Like porcelain and bone china, stoneware is non-porous, hard and water resistant. However, unlike earthenware, stoneware – like bone china and porcelain – is a vitreous ceramic, which means it contains glass; this results in a product that is suitable for holding liquids without the need for glazing, although products such as tableware and decorative objects are often glazed to give an attractive finish. Stoneware is more chip-resistant than earthenware, and more opaque than porcelain. It is usually grey or brown in colour due to impurities in the clay. The British tableware manufacturer Wedgwood uses stoneware in a specific form, known as Jasperware, which is marked out by its distinctive, rough, pale blue, textured finish.
Different types of stoneware are available, from traditional stoneware – which is dense and inexpensive, made from secondary clays – to chemical stoneware, which is made from purer raw material and can be used to create large vessels for storing highly corrosive liquids such as acid.
Image: Work table lamp by Dick van Hoff
Key features
•Stone-like quality
•Not easy to work as a clay
•More stable in the firing than clay
•Vitreous, making it water resistant
•Good abrasion and wear resistance
•Good electrical resistance
•Non-porous
•Fires at 1183ºC (2161ºF)
Sources
Widely available.
Cost
Varies according to grade, but generally inexpensive.
As an inert material, ceramics do not degrade. In order to produce ceramics an irreversible chemical reaction needs to take place, therefore, unlike thermoplastics, which can be reheated and reused, ceramics are not recyclable in the sense that they cannot be re-moulded. However, they can be crushed and used as fillers and gravel for various industrial applications. The main issue with ceramics is the intense heat that is used during firing, and often, when a ceramic needs glazing, this will involve a second firing process.
Production
As with bone china, the strength of stoneware means it can be formed into thin wall sections, which are suited to slip casting. Traditional methods of ceramic production also apply, such as turning, extrusion, jigger jollying and compression moulding.
Typical applications
The hard and vitrified nature of stoneware means it has applications as water-resistant tableware without the need for glazing. As a highly vitrified ceramic it is also widely used in chemical and electrical products due to its good electrical resistance and low water permeability.
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–Very hard –Water resistant –Low cost –Good electrical resistance –Good wear resistance |
–Not recyclable –Energy intensive to produce |