Incense making in India is closely related to Ayurvedic practices. Perhaps in modern times, the use of chemicals and other not-so-ayurvedic practices have become common, though I imagine the traditional methods are still widely used.
Our friend Wiki says that Ayurvedically, the ingredients that go into incense are categorized into one of 5 classes, which are the elements: Ether (fruits), Earth (roots), Fire (flowers), Water...