Ceylon 1877 QV 64c Die Proof Before Hardening, Rare

1877 DIE PROOF in black for QV 64c (SG 131 & 140) on glazed card marked BEFORE HARDENING and dated APR 19 1877. A rare die proof for this interesting stamp being one of only two 1877 values and then for the trio later sent to Ceylon but only issued with surcharges..