In Hindu temples, the original icon in the garbhagṛha or sanctum sanctorum, called ‘dhruvabera’ is generally made of stone and is permanently fixed. As the temple rituals evolved into elaborate proportions, the need for a subsidiary image, a replica or a representative of the original, also arose. It was this image that was taken out in procession on festival days. Hence it was called ‘utsava-mūrti’ or ‘procession-image.’ Such images—also any portable image used in ritualistic worship—were mostly prepared out of ‘aṣṭadhātus’ or eight metals viz., gold, silver, iron, tin, lead, copper, zinc and mercury (or brass).
Sometimes the term ‘aṣṭalohas’ is also used for the same.