Great Britain 1840 1d Deep blue 'Rainbow trial' (State 3). SG DP20Great Britain 1840 1d Deep blue 'Rainbow trial' State 3(a), SG DP20. Superb unused bottom left hand corner marginal example with manuscript endorsement to margin 'F' Pruss' by Edwin Hill. These were produced to test various combinations of stamp and cancellation ink. The voided corners of State 3 are more uniform in shape compared with the ragged corners of States 1 and 2. Most attractive and scarce. Accompanied with a 1996 Royal Philatelic Society