Is obsidian sourcing about geochemistry or archaeology? A reply to Speakman and Shackley

► Many important issues facing sourcing research have little to do with pXRF itself. ► Validity and reliability, concepts from evaluation theory, are often misunderstood. ► Sourcing “results” are more than merely reporting an instrument's raw measurements. ► Simple accuracy tests alone cannot validate or invalidate a technique for sourcing. ► pXRF will ultimately improve reproducibility and results in archaeological research.