Researchers from the National Institute of Technology (NIT) Rourkela have developed an eco-friendly method to produce black terracotta wares. This unique process merges traditional artisan knowledge with modern technology to produce black terracotta sustainably.
The research team, led by Prof. Swadesh Kumar Pratihar, Professor of Ceramic Engineering, along with Mr. Shiv Kumar Verma, Senior Technical Assistant, and Dr. Rupesh Mandal, a Research Graduate from NIT Rourkela, has secured a patent (Patent No. 572754, Application No. 202531008090) for the developed process.
The word, Terracotta, is derived from the Italian language, which means “baked earth”, and has been extensively used in India for kitchenware (utensils), temple sculptures, and roofing tiles. Red terracotta is commonly seen, which is made by firing common clay in the presence of air. The presence of iron in the clay, when exposed to fire, leads to oxidation, resulting in its characteristic red color. In chemical terms, ferric oxide produces the red colour in the process. On the other hand, Black terracotta wares are known for their contrasting shine and mirror finish.
Black pottery is made in India and its neighbouring regions using techniques that are generations old. One such example is the Nizamabad Black Pottery of Uttar Pradesh, where semi-finished wares are coated with a glaze made of clay and organic vegetable matter native to the area, referred to as “kabiz.” Polishing with mustard oil gives the surface a mirror finish. It is then fired in a sealed iron vessel along with cow dung, straw, and wood chips. Crafting beautiful black ware requires time, effort, constant monitoring, specialized clay, skilled hands, and organic fuel in solid form.
In Tibet’s Nixi village, artisans use coarse red clay mixed with white sand and powdered black baked quartz. The wares are covered with wood logs during firing, and once the desired temperature is reached, the fire is extinguished using sawdust. The smoke produced in this final step turns the pottery black.
The existing production method typically requires 2 days to complete the open-pit firing process, which releases smoke containing many toxic gases, such as carbon monoxide, carbon dioxide, sulfur oxides, and nitrogen oxides, that adversely affect the health of associated workers, including breathing difficulties.
With the aim of eliminating the major drawbacks of these generation-old processes and focusing on sustainable development, the patented method developed by Prof. Swadesh Kumar Pratihar and his team reduces the total firing process to less than 7 hours without any adverse impact over the health of working associates and climate.
Speaking about the patented process, Prof. Swadesh Kumar Pratihar, Professor, Ceramic Engineering, NIT Rourkela, said, “The sustainable production process merges traditional artisan knowledge with modern technology. The Key to this process is the indirect heating of as-fabricated bodies 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.”
This method produces a uniform black finish and does not require open fires, skilled worker, or specialised clay. The process significantly shortens the firing cycle and eliminates environmental pollution associated with burning large quantities of organic materials. Unlike older methods, this approach can be a key technology to produce black terracotta wares, anywhere.
The process developed by NIT Rourkela researchers makes a significant contribution to environmental conservation and heritage preservation.