The earthen mix turned out to be a blessing, since the cannabis played a key role in preserving the World Heritage site.
According to Manager Rajdeo Singh, an archaeological chemist of the Archaeological Survey of India’s science branch (western region), and Milind M. Sardesai, who teaches botany at Dr Babasaheb Ambedkar Marathwada University, the mixture prevented the plaster from degrading for over 1,500 years.
The Ellora caves were built between the 6th and 11th centuries, A.D. in the western state of Maharashtra. They are made up of a group of 34 temples carved out of stone and are dedicated to the three main religions of India — Buddhism, Hinduism and Jainism.
The structure runs in a north–south direction for about 1.2 miles. At the southern end are 12 Buddhist caves, in the north are six Jain caves and in between lie 17 Brahmanical caves.
“The caves are breathtaking examples of rock-cut architecture that stands testimony to the imagination and artistry of its creators,” Singh and Sardesai wrote in the journal Current Science.
They analyzed the clay plaster of Buddhist cave no. 12, a remarkable three-storied building.
Using a scanning electron microscope, infrared spectroscopy and stereomicroscopic studies, the researchers were able to isolate specimens of cannabis from the clay plaster.
The remains of cannabis, popularly known as ganja or bhang in India, suggest that it was used in the clay and lime mixture mainly as an insulating agent and to provide added strength to the plaster.
“The cannabis fiber appears to have a better quality and durability than other fibers. Moreover, the cannabis’ gum and sticky properties might have helped clay and lime to form a firm binder,” Sardesai told Discovery News. Called hempcrete, the concrete-like substance used for plastering provided “a healthy, comfortable and aesthetically pleasing living environment to the Buddhist monks to stay,” the researchers said.
“As the hemp plaster has the ability to store heat, is fire-resistant and absorbs about 90 percent of airborne sound, a peaceful living environment for the monks has been created at Ellora Caves,” they added.
Studies in Europe have estimated that hempcrete can last 600–800 years. In the Ellora caves the life span doubled despite damaging environmental factors, such as a growing humidity inside the caves during rainy seasons.
“Ellora has proved that only 10 percent of cannabis mixed with clay or lime in the plaster could last for over 1,500 years,” Singh told The Times of India.
In contrast, hemp wasn’t used in the neighboring Ajanta, another World Heritage site consisting of about 30 rock-cut Buddhist structures dating back to the 2nd century BC.
There, “rampant insect activity has damaged at least 25 percent of the paintings,” Singh said.
According to the researchers, properties of hemp fibers such as the ability to regulate humidity inside the cave, pest resistance, fire-retardant, non-toxicity, high vapor permeability, hygroscopic properties, were known to the inhabitants of Ellora in the 6th century AD.
“Unfortunately in India cannabis has gained a bad name because of its narcotic properties. But the ancient artists knew its good sides,” Sardesai said.
Lorenzi, Rossella. 2016. “Hemp Walls Saved India's Ancient Ellora Caves”. Discovery News. Posted: March 11, 2016. Available online: http://news.discovery.com/history/archaeology/hemp-walls-saved-indias-ancient-ellora-caves-160311.htm