Imperial Russia - Romanov Dynasty issue

Imperial Russia - Romanov Dynasty issue
1913, Romanov Castle, stage proof of 3r in black, engraved printing on thin creamy paper, mounted on sunken white card, proof size 45x33mm (top right corner clipped), card size 71x50mm, slight traces of mounts, VF and extremely rare, according to Robson Lowe the only card produced, which is similar to proofs on India paper made by American Bank Note Co., Est. $1,500-$2,000, Scott #103