Proof A portion of the sheet cut into a "T" shape showing a single impression in a shade of deep blue, on white wove paper, cancelled with "No712" in black which shows signs of attempted removal with Tartaric acid, manuscript "C3" changed to "A1" and C. dipt CW A Co Tartaric Acid" in J.B. Bacon's handwriting. S.G. Spec. DP20F. Photo in colour