Sacagawea and the Lab: Alloy Exploration

Nearly twenty years ago, when the world had barely survived the Y2K bug, Corrosion Testing Laboratories, Inc. set out with the US Mint to explore different options that were viable for the new $1 coin.  The world has moved more and more to instant purchases and the almighty plastic card.  But, regardless, the U.S. Mint set out to revive the dollar coin inventory.

Dollar coins were first minted in the United States in 1794.  In 1849-1889, the coin was 13 mm and easily lost. In the 20th century the coin had little popularity even with a try to increase usage in 1971.  In 1997, Congress authorized the minting of The Sacagawea dollar.  This was driven because the inventory of the last mintage in 1981 was expected to soon be depleted. These coins have a copper core clad by manganese brass.

The U.S. Mint provided different alloy combinations and these materials were subjected to an accelerated corrosion test at CTL.  The medium used was to simulate sweat from contact in hands that the coins were expected to come in contact with.  Natural salts and oils can degrade these materials.  In addition, humidity and temperature were used to accelerate the aging process.  Ultimately, the U.S. Mint reviewed the exposure findings to determine which unique alloy was most suitable for this application.

Read the full article about CTL’s involvement here: Read the full article here

Check out more information about the history of the dollar coin here (