Bhasma is the holy ash produced from the Homa, the sacrificial fire, wherein special wood along with ghee and other herbs are offered as a part of pooja. By the time a Bhasma is formed, no trace of original matter remains in the ash. Ash obtained from any burnt object is not bhasma.
The ritual involves worshipping the deity by pouring ash as abhishek and then distributing it as Bhasma, which is then applied on the forehead (usually), upper arms, chest, or rubbed all over the body. Some consume a pinch of Bhasma when they receive it.
The word Bhasma is derived from bha or “bhartsanam” (“to destroy”) and “sma” or “smaranam” (“to remember”). It denotes “that by which our sins are destroyed and the Lord is remembered”. Bhasma is also called vibhuti, which means glory. Bhasma is associated with Lord Shiva who applies it all over His body.
Spiritually, the Homa is the offering of oblations into the fire with sacred chants and signifies offering or surrender of the ego and egocentric desires into the fire of knowledge. The resultant ash signifies the purity of the mind. The fire of knowledge burns the oblation and wood signifying ignorance and inertia respectively.
The application of ash implies that one should burn false identification with the body.
Bhasma has medicinal values in Ayurveda. It is supposed to be the strongest of all Ayurveda preparations. Ayurveda defines Bhasma as when the matter is converted into non matter by the process of homa. The non matter is the spirit or the energy of the matter being processed with strong healing powers. It has the same significance as any ‘potentised’ medicine in homeopathy.
It absorbs excess moisture from the body and prevents colds and headaches.
When applied with a red spot at the center, the mark symbolizes Shiva-Shakti (the unity of energy and matter that creates the entire seen and unseen universe).
The Upanishads say that the famous Mrityunjaya Mantra should be chanted whilst applying ash on the forehead.
(Disclaimer: The views expressed in this write up are my own).