What is the chitraveena slide made of?

The chitraveena slide, the gottu, is a cylindrical block held in the left hand and glided over the melody strings. Reported materials include ebony or other hardwood, bison or buffalo horn, glass and steel. In the late 1980s N. Ravikiran adopted Teflon slides, on the advice of the scientist Hemmige D. Varadarajan, to cut slide noise.