The Clef du Vin website doesn’t tell what metals are in their product. They say only, “What does the alloy contain? The answer forms the basis of four international patents.” However, I have found a number of websites that recommend using copper or silver to correct wines that are “reduced” and have sulfur-derived off-smells (e.g., burnt rubber; see http://www.wineloverspage.com/wineadvisor1/tswa060120.phtml). Tom Ciocco ... talks about reduced wines (http://terroir.winelibrary.com/2007/02/12/reduction-augment-your-understanding/), but he doesn’t mention copper or silver.