This very rare libation cup is from a segment of coconut shell, probably a Seychelles nut (coco-de-mer). It is inscribed around the rim with four sections of Sanskrit script. It is in oval form and fits well across the palm of the hand.
It would have belonged to a Hindu ascetic or sadhu, probably in one of the holy pilgrimage cities such as Benares.
The form emulates the skullcups or kapala made from the top sections of human skulls that were used in Tibetan Buddhism. Such cups in human skull generally were not used in Hindu Tantric ritual because Hindus cremate (as opposed to the Tibetan who traditionally used sky-burial which saw the main skeletal bones remain intact.) In place of a human skull dish, Hindu ascetics could use coconut shell.
The example here has superb and obvious age and a glossy, dark patina. The rim has been rounded and softened by years of use. The four sections of Sanskrit are carefully and deeply inscribed into the shell. They have been filled with what is probably orange-red sindhoor powder, allowing them to stand out against the dark shell.
The shell is in excellent condition. This is the first time that we have encountered such a cup.
(The final image shows a group of sadhus, seated, northern India, around 1900.)
Hartsuiker, D., Sadhus: Holy Men of India, Thames & Hudson, 1993.