1,184 silver cob coins in various degrees of degradation were recovered from most parts of the “Tortugas” shipwreck site, but with a heavy concentration in the stern. The coins tended to be scattered, lying individually rather than in large concreted clumps.
To produce cob coins, silver with the requisite fineness of 92-98% purity was hammered into crude bars with slight variances in thickness. Pieces of the bar were cut to approximate size, weighed and the edges clipped until the blanks fell within authorized weight requirements. These planchets were then reheated, placed between dies and struck to imprint the crowned Shield of the House of Habsburg on the obverse and a cross with the Lions of Leon and Castles of Castile in the four quadrants of the cross on the reverse. Coins produced in the South American mints at Potosi, LaPlata, Lima, Bogota and Cartagena featured a Greek cross. Those from the Mexico mint held the Florenzada cross. The image was frequently off center, and because both sides were imprinted simultaneously the image is often more pronounced on one side. Since the thickness of the coin also varied, the strike may be clearer from one point to another over the surface. Cob coins were thus never round or even.
From the sample of 1,184 silver "Tortugas" wreck coins initially examined, 53.5% of the assemblage comprised 8 reales, 22.1% 4 reales, 11.3% 2 reales, 13.0% 1 reales and 0.1% ½ reales. Two coins were of the c. pre-1572 pillar design. Most common were 8 reales issues minted in Mexico. A further 212 8 reales issues derived from Potosi. Third most common were 157 4 reales from Mexico, followed by 104 1 reale from Mexico. In total, 56.0% of the silver coins originated in Mexico, 29.9% in Potosi and 1.1% in Bogota/Cartagena or an Old World mint.