In the historical Vedic religion, Pravargya was a ceremony introductory to the Agnishtoma (Soma sacrifice), at which fresh milk is poured into a heated vessel called mahavira or gharma and offered to the Ashvins. The ceremony is described in details in the technical texts on proper ritual, the Brahmanas, Aranyakas and Shrautasutras.
The ritual
The whole Pravargya ritual has two distinct parts: the preparation of the earthen implements, especially the gharma or mahavira and the rites performed on the latter immediately after taking out of the furnace. These rites include the offering of hot milk to the Ashvins, and repeating it in the evening and so for three consecutive days preceding the upasad. At its conclusion, the implements used in this ritual, particularly the mahavira are carried in procession to uttaravedi and buried there.