The first and only case when platinum coins were used as a regular national currency was in Russia, where coins were circulated between 1828 and 1845. These coins proved to be impractical: platinum resembles many less expensive metals, and, unlike the more malleable and ductile silver and gold, it is very difficult to work. However, merchants valued platinum coins because it did not melt in fires like gold or silver. The minting of platinum coins resumed only after 130 years. Between 1977 and 1980, in preparation for the 1980 Summer Olympics, the Soviet Union produced five commemorative coin sets, and since 1988 commemorative platinum coins were issued every year. The practice of regularly issuing platinum coins has continued in modern Russia, and since 1992 the Central Bank of Russia has released 16 sets of platinum coins.