1872 - 1879 4d - A Die Proof in black on glazed card (92mm x 60mm) marked AFTER HARDENING and dated June 6 1879, initialled in lower left corner and subsequently endorsed “Sir is this to be a plate of 30”,the reply “Yes” initialled by Warren William De la Rue. With an earlier Die Proof in black on glazed card (92mm x 60mm), marked BEFORE HARDENING and dated May 31 1879. A unique pair. Ex Dr Joan Harper and Vestey collections