What is the black spot on a tabla?

The black spot on a tabla is the syahi, a disc of loading paste, set in the centre of the dayan and off-centre on the bayan. Sources name starch or dough, iron filings or iron oxide, gum, and charcoal or soot among its ingredients. In 1920 Raman and Kumar showed that this loaded head gives harmonic overtones in the same relation to the fundamental as a string.