100 Soles de Oro Law# 10535; black reverse

Law 10535, passed in 1950, consolidated Peruvian currency under the Banco Central de Reserva and authorized this series. The black reverse was a deliberate security measure — an alternative color scheme introduced partway through the series run to complicate counterfeiting, which had become a documented problem with the earlier printings. De La Rue's London plant handled the full production, as it had for Peruvian issues going back decades, giving Lima's central bank a reliable but expensive offshore dependency for its highest-denomination circulation notes.

The black-reverse variant is cataloged separately from the earlier issues precisely because the color change was not cosmetic.