The tradition's claim is that the skulls are pre-Columbian ritual objects, some even superhuman in origin. The scientific findings are consistent and specific. Scanning electron microscopy of the carved surfaces, reported by Sax, Walsh, Freestone, Bevan and Meeks in the Journal of Archaeological Science in 2008, revealed the regular, straight, parallel grooves left by rotary lapidary wheels, and, on the Mitchell-Hedges skull, marks from a diamond-tipped rotary burr under two millimetres across.
Pre-Columbian carvers worked quartz by slow hand abrasion, which leaves a very different, irregular signature. Trace-element and inclusion studies further indicated the quartz came from Brazil or Europe, not from Mesoamerican sources. Together these results place the skulls firmly in the nineteenth and twentieth centuries. The British Museum and the Smithsonian, custodians of two of the studied skulls, present them accordingly as modern objects. No crystal skull has ever been recovered from a documented pre-Columbian context.