United States. Bureau of the Mint. "2014 Biennial Report to the Congress : Appendix 4: Alternative Metals Study Phase II: Technical Report (August 11, 2014)," Biennial Report to the Congress as required by The Coin Modernization, Oversight, and Continuity Act of 2010 (Public Law 111-302) (December 2014). https://fraser.stlouisfed.org/title/9414/item/687740/content/pdf/usmint_2014-Biennial-Report-appendix-4, accessed on July 27, 2026.