20 Mil Réis Thesouro Nacional, 3rd print

Perkins, Bacon & Petch — at the time still operating under that transitional name before settling as Perkins, Bacon & Co. — were the dominant security printers of the mid-nineteenth century, best known for their siderographic steel engraving process, which made plate duplication and counterfeiting exceptionally difficult. Brazil's Imperial Treasury turned to them repeatedly across multiple print runs of this series, a reasonable choice for a government that had been battling note forgery since the 1820s.

The "3rd print" designation matters here. Each successive print run of this denomination carried subtle differences in plate state and overprint details, and misidentification between runs is common. Collectors distinguishing between them should focus on the serial number typography and any manuscript annotations rather than the core engraved design, which remained largely consistent across printings.