NIT Rourkela gives ancient terracotta a modern, eco-friendly upgrade

Researchers from the National Institute of Technology, Rourkela, have developed a new environment-friendly process to manufacture black terracotta wares. The procedure merges traditional pottery with modern engineering and has finally been granted a patent.

The work was headed by Professor Swadesh Kumar Pratihar, Professor of Ceramic Engineering. The group consists of Mr. Shiv Kumar Verma, Senior Technical Assistant, and Dr. Rupesh Mandal, a research scholar at NIT Rourkela.

'Terracotta' in Italian means "baked earth." It has been part of the Indian craft traditions for several centuries.

Red terracotta is common and is produced by firing clay in the presence of air. Iron in the clay oxidises during firing, giving it the familiar red colour.

Black terracotta, on the other hand, has a shiny, mirror-like finish and requires totally different techniques.

For ages, black pottery has been produced all over India by slow and time-consuming processes. Nizamabad's black pottery is just one example from Uttar Pradesh.

A glaze prepared with local clay and organic matter called “kabiz” is applied by artisans. The surface is polished with mustard oil and fired in sealed vessels filled with cow dung, straw, and wood chips.

This finish stage requires skill, close supervision, and specialized clay.

There are similar traditions found elsewhere. In the village of Nixi in Tibet, red clay is combined with white sand and baked quartz.

After this, the pottery is smoked using sawdust to turn it black. Most of these methods take two days and rely on the burning of large amounts of organic fuel.

They also emit toxic gases which may be harmful to workers.

This is what the NIT Rourkela team wanted to address. The patented process reduces the firing time to less than seven hours; neither does it involve open fires nor any smoke is generated.

The new process also removes the need for rare clay types or highly skilled artisans.

According to Professor Pratihar, the trick lies in heating the pottery in a vacuum, where there is little or no air. During heating, carbon-rich oil breaks down and produces carbon monoxide and soot.

This creates the reducing atmosphere needed to produce the black colour without polluting the environment.

The method yields a uniform black finish. Application of the described method is possible in any region. It avoids health hazards, there is no burning of organic material, and it makes traditional knowledge compatible with modern manufacturing. The researchers say the process will support sustainable production while helping keep terracotta craftsmanship alive.