New Delhi: Researchers at the National Institute of Technology (NIT), Rourkela, have developed and patented an environmentally-friendly technique for manufacturing black terracotta wares.
The research team led by Swadesh Kumar Pratihar of Ceramic Engineering along with Senior Technical Assistant Shiv Kumar Verma, and research scholar Dr Rupesh Mandal, have merged traditional artisan knowledge with modern technology to produce black terracotta, which means “baked earth”, sustainably.
In India, it has been extensively used for kitchenware, temple sculptures, and roofing tiles. The most common variety is red terracotta, made by firing clay in the presence of air. While the presence of iron in the clay, when exposed to fire, leads to oxidation, resulting in its characteristic red colour, black terracotta wares are known for their contrasting shine and mirror finish.
A case in point is Nizamabad Black Pottery of Uttar Pradesh, where semi-finished pieces are coated with a local glaze called “kabiz” (made from clay and plant-based organic matter), polished with mustard oil for a glossy mirror-like surface, and then fired inside sealed iron containers packed with cow dung, straw, and wood chips.
However, traditional open-pit firing, which normally takes around two days, generates thick smoke loaded with poisonous gases including carbon monoxide, carbon dioxide, sulphur oxides, and nitrogen oxides, causing severe respiratory problems and other health issues for the artisans.
Eco-friendly upgrade
This innovative sustainable method cuts down the entire firing duration from the conventional two days to under seven hours, while completely eliminating any harmful effects on the health of workers and the environment, the institute announced on Monday.
Stating that the sustainable production process merges traditional artisan knowledge with modern technology, Professor Pratihar explained that the key lies in heating the pottery in an enclosed vacuum (air-depleted) chamber. “During this heating, pyrolysis of the carbonaceous oil produces carbon monoxide and carbon soot, which helps in producing the reducing atmosphere required for the development of back colour wares,” he added.
This method delivers a uniform black finish and can be a key technology to produce black terracotta wares, anywhere, without the use of open fires, skilled workers, or specialised clay. Besides protecting the environment, it can also preserve India’s rich pottery heritage.