Belgian Congo, Banque du Congo Belge, a group of development and production materials for the 500-Franc note by the American Bank Note Co., including face and back approval Proofs in black, a face and back in blue on banknote paper, the face with serial numbers and series letter attached to show position, engraved vignettes, a model of a vignette, also a full-color model of an unissued 20-Franc note, a fascinating offering of very rare and unique items, all in a high degree of preservation