By the 1980s, when the Getty Museum began to hoover up old private collections including one belonging to Sam Wagstaff, a legendary collector with an original eye and a personal fortune collectors and curators all had to know exactly who was who, and who had changed the medium.

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He treats Italy like his own private attic, coaxing a few famous but mostly obscure old masters out of private collections, regional museums, palaces and churches.

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Other strategic loans to fill occasional historical gaps remind us of the amazing old-master paintings still in private collections.

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"Because designers are jumping from one house to another so quickly, we wax nostalgic for collections that are not that old, " said Cameron Silver, co-owner of the Los Angeles vintage store Decades.

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Most of them were returned after 1815, but the French royal collection remained accessible in the Louvre, and it was in England, with spectacular private collections but no national gallery, that old-master exhibitions were first established.

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