To qualify as treasure trove, an object must be precious, it must be hidden, and there must be no proof of its property or reasonable presumption of its former ownership. Unlike under English common law, treasure is not restricted to only gold and silver objects. In 1888 a prehistoric jet necklace and some other articles found in Forfarshire were claimed by the authorities though they were neither gold nor silver. A compromise was eventually reached, and the find was deposited in the National Museum of Scotland. In July 1958, a porpoise bone was found together with 28 other objects of silver alloy (12 brooches, seven bowls, a hanging bowl and other small metal work) underneath a stone slab marked with a cross on the floor of St. Ninian's Church on St. Ninian's Isle in Shetland. The objects were dated to c. AD 800. A dispute having arisen over ownership of the objects between the Crown on the one hand, and the finder (the University of Aberdeen, which had carried out the archaeological excavation) and the landowner on the other, in "Lord Advocate v. University of Aberdeen" (1963) the Court of Session held that the bone should be regarded as treasure trove together with the silver objects. Further, the requirement that an object must be "hidden" means no more than that it must be concealed; it refers to the condition in which the object was found and does not refer back to the intention which the owner of the object may have had in hiding it. Finally, the requirement that there must be no reasonable presumption of former ownership means that it must not be possible to trace the ownership of the object to a person or family currently existing. Even if an object does not qualify as treasure trove, it may be claimed by the Crown as "bona vacantia".