1989, $2.40 Moon Landing, Background in Gray. Chemically altered at the Bureau of Engraving and Printing by chemical wiping of the blue ink, plate block of 4, o.g., never hinged, Very Fine, an unusual B.E.P. experimental "essay", reported that only 16 stamps were treated as such. Scott No. 2419 var.  Estimate $2,000 - 3,000. $0 (Image)