Crucifixion gem

ETC BLOG: Depiction of Crucifixion (SBL Report) (Peter M. Head). The gem is of interest for its early (c. 200 CE) iconography of crucifixion and of the appearance of Jesus. That said, I would like more clarification about its provenance (it seems to have been "acquired" rather than excavated archaeologically) and how certain specialists are (and on what grounds) that it is genuine.