Dinero 'negro' - Alfonso X

Alfonso X's monetary reform of 1258 introduced these low-grade billon pieces as part of a deliberate crown policy to retire the older, heavier dineros and replace them with a coinage whose intrinsic value sat well below its face value — an early and relatively crude attempt at fiduciary currency. The high copper content darkens these coins noticeably on the surface, which is where the popular "negro" designation originates. Alfonso's broader monetary ambitions repeatedly outpaced his administration's ability to enforce them, generating chronic hoarding of better silver and a flood of complaints from merchants throughout Castile.