Postage stamps and postal history of Costa Rica change in currency from "Reales" to the new Pesos and "Centavos", the issue of 1863 was surcharged with new values for postal use: 1 Centavos, 2 Centavos, 5 Centavos (all over the Medio Real stamp), 10 Centavos (over Dos Reales) and 20 Centavos (over Cuatro Reales). The 5, 10 and 20 Centavos were also surcharged "U.P.U." Costa Rican stamps were issued overprinted "Guanacaste" in 1885-89 following war with Nicaragua over the sovereignty of Guanacaste. The first issue in the new "Colón" currency was dated 1900 and put into circulation in 1901. It consists of ten stamps with values ranging from
Gold standard to Congress the value of a decimal system. This system would also apply to monies in the United States. The question was what type of standard: gold, silver or both. The United States adopted a silver standard based on the Spanish milled dollar in 1785. From 1860 to 1871 various attempts to resurrect bi-metallic standards were made, including one based on the gold and silver franc; however, with the rapid influx of silver from new deposits, the expectation of scarce silver ended. The interaction between central banking and currency basis formed the primary source of monetary instability during this period.