1/2 Real Preto – João I Porto mint

João I's reign saw Portugal pivoting aggressively toward Atlantic expansion — Ceuta fell to Portuguese forces in 1415, the same year this type enters production. The billon coinage of this period reflects chronic silver shortages that plagued the Portuguese treasury throughout the early fifteenth century, forcing repeated debasements that pushed alloy fineness to the floor.

The Porto mint attribution distinguishes this from contemporary Lisbon issues; Porto's output was generally smaller in volume and draws accordingly more collector attention today. Gomes J1 39 is among the lower-denomination billon types of João I's extensive coinage reform program.