Terracotta has been used since the earliest times – for example, the terracotta army from China dates back to 210–209 BCE. One of the simplest expressions of earthenware ceramics, terracotta is the material used in flowerpots but behind its suntanned, digestive biscuit texture lays an interesting scientific phenomenon that actually contributes a functionality to the product that most people are unaware of.
Translated from the Italian for baked earth, terracotta is unglazed, semi-fired clay with a distinctive dry, creamy red biscuity texture, which is obtained through washing the clay and mixing in only the finest particles of sand. Although the red variety is the most common, it is also found in yellow and even a milky white, depending on where it is mined.
In relation to its use in flowerpots, the porosity of terracotta gives it one of its distinguishing and unique features. It is because of its pores that an interesting osmotic effect is produced, allowing for natural evaporation of water through its surface. It’s this property, combined with its low cost, that makes terracotta such a good material for flowerpots. Plants drain more easily and dry earth can be kept wet through this osmotic process. The effect has also been used in traditional water containers to keep drinking water cool in hot climates, an application which has been interpreted in a contemporary design of a bottle by Royal VKB. This application also highlights the novel combination of traditional terracotta with a modern silicone rubber foot.
Image: Terracotta carafe by Royal VKB
Key features
•Wicking effect
•Straightforward to form
•Low cost
•Low density
•Porous
•Low firing temperature
Sources
Terracotta is a widely available clay, and can be found in various parts of the globe.
Cost
Relatively inexpensive.
Sustainability issues
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. Due to the fact it fires at a relatively low temperature and is unglazed, terracotta is less energy intensive to produce than many other ceramics.
Production
As with many traditional ceramics, terracotta can be slip cast, turned on a lathe, jigger jolleyed and formed on a potter’s wheel.
In India, chai was served to railway passengers in terracotta cups, which were then thrown out of the window when the chai was drunk. Another unusual application exploits the acoustic properties of ceramics, resulting in the use of terracotta in speakers. More general applications include it being used as a material for exterior applications such as tiles, plant containers and hollow building bricks because of its ability to withstand frost. Apart from the bottle shown here, it is also used in wine bottle coolers, where soaking the terracotta in water naturally cools the wine.
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–Versatile production –Low cost –Natural wicking |
–Not recyclable –Energy intensive to produce, though less so than many other ceramics |