The private ownership of great art, its seclusion from the general view of men and women, let alone from that of interested amateurs and scholars, is a curious business. The literal disappearance of a Turner or a Van Gogh into some Middle Eastern or Latin-American bank vault to be kept as investment and collateral, the sardonic decision of a Greek shipping tycoon to put an incomparable El Greco on his yacht, where it hangs at persistent risk - these are phenomena that verge on vandalism.