McAteer JA, Williams JC, Cleveland RO, Van Cauwelaert J, Bailey MR, Lifshitz DA, Evan AP. Ultracal-30 gypsum artificial stones for research on the mechanisms of stone breakage in shock wave lithotripsy. Urol Res. 2005 Dec;33(6):429–34. doi: 10.1007/s00240-005-0503-5. PMID: 16133577.