In 2003 the Banco de México began the gradual launch of a new series of bimetallic $100 coins. These number 32 – one for each of the nation's 31 states, plus Mexico City. While the obverse of these coins bears the traditional coat of arms of Mexico, their reverses show the individual coats of arms of the component states. The first states to be celebrated in this fashion were Zacatecas, Yucatán, Veracruz, and Tlaxcala. In circulation, they are extraordinarily rare, but their novelty value offsets the unease most users feel at having such a large amount of money in a single coin. Although the Bank has tried to encourage users to collect full sets of these coins, issuing special display folders for this purpose, the high cost involved has worked against them. Bullion versions of these coins are also available, with the outer ring made of gold instead of aluminum bronze.