In 2004, an analysis of the ossuary's petrography and oxygen isotopic composition was conducted by Avner Ayalon, Miryam Bar-Matthews and Yuval Goren. They compared the "δ"18O values of the letters patina from the James Ossuary, with the patina sampled from the uninscribed surfaces of the same item ("surface patina"), and with surface and letters patinas from legally excavated ossuaries from Jerusalem. Their study undermined the authenticity claim of the ossuary. However, Dr James Harrell, professor of Archaeological Geology at the University of Toledo, provided an explanation for this "δ"18O discrepancy. He suggested that a cleanser may have been the source of the low "δ"18O readings, which antiquities dealers and collectors often use to clean the artifacts to increase value. He tested the most popular cleanser sold in Israel and confirmed that the "δ"18O value of the cleanser was consistent with the "δ"18O value of the patina in the inscription.