DONALD JUDD

The record for a Judd -- and for any minimalist work -- was set in May 2002 at Christie's in New York, when a major untitled piece from 1966-67 went for $4,629,500. (Prices include auction-house premiums.)

Over the last three or four years, other major Judds have tended to go for around $1 million -- often well above their estimated prices.

In the middle 1980s, you could have bought important Judds for less than $50,000, and would never have paid more than $100,000.

DAN FLAVIN

The record for a Flavin was set at Christie's in New York this May, when a 1964 light-piece called "Alternate Diagonals of March 2, 1964 (To Don Judd)" -- the work was made in an edition of three -- sold for $679, 500. An identical piece from the same edition sold in 2002 at Christie's for $405,500. And precisely the same object that set the Flavin record in 2004 had already come to auction in 2000, at Sotheby's New York, where it sold for $335,750 -- almost double its high estimate.

Of course, if you had tried to buy the same kind of Flavin at auction back in the 1980s, it would have cost you at most about $30,000.

-- Blake Gopnik

This untitled Donald Judd piece was part of the recent show at the Tate.