The five-metal alloy is prescribed in the Shilpa Shastra textual tradition, but secondary accounts date the relevant texts anywhere from the fifth to the ninth century CE depending on the recension, with no single scholarly source consulted confident enough to cite for a precise date. The Chola dynasty, ninth to thirteenth century CE, is where panchaloha temple bronze casting is best documented and most celebrated, but that is its flowering rather than its documented beginning.
What would resolve this A South Indian art history or Sanskrit textual scholarship source establishing when the specific Shilpa Shastra passages prescribing the five-metal alloy were composed, distinguishing that from the later Chola-era flowering of the practice.
OpenSouth Indian art history and Sanskrit textual scholarshipDenise Cush, Catherine Robinson and Michael York (eds.), Encyclopedia of Hinduism