Tulipmania! That one-word definition of irrational market exuberance came to mind during Christie’s New York sale of post-war and contemporary art on the evening of May 9, 2006, as lot 25 came to the block. A galvanized metal box, roughly two feet square and six inches deep, covered with a blue plastic lid -- an untitled Donald Judd sculpture from 1985 -- the work carried a presale estimate of $300,000-$400,000, and followed the sale of two dozen similar boxes for similarly high prices. $300,000 for a shallow metal box? The mind reeled. But then auctioneer Christopher Burge knocked it down to a phone bidder for $450,000 ($531,200 with the auction-house premium), and the art world snapped back into focus.