Mustard Mystery 

    Kids, is there really silver in that silver coin?  Even though our dimes, quarters, half dollars, and "silver" dollars are silver in appearance, those minted after 1971 actually have no silver in them. Silver was completely removed from dimes and quarters in 1965 and replaced with an outer layer of copper-nickel alloy bonded to an inner core of pure copper. The half dollar and "silver dollar" followed suit in 1971.  Believe it or not, our "copper" pennies nowadays are mostly zinc and our "silver" coins are mostly copper!

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    Dimes and quarters minted before 1965 were composed of an alloy of 90% silver and 10% copper, and they are considered somewhat valuable by collectors. You can easily test for the presence of silver with a simple experiment. Using a plastic knife, apply a generous portion of mustard (yes, the yellow stuff you put on your hotdog) to both pre-1965 and post-1965 dimes and quarters. Let them sit overnight on a paper towel. The next day, rub off the mustard. A black spot will remain on the true silver coin but not on a non-silver coin.

    What's happening? Mustard contains natural sulfur compounds. Sulfur is an element that is very common in our day-to-day world. Sulfur reacts with the silver to form a black powder (a "precipitate") of silver sulfide. The chemical formula for silver sulfide is Ag2S. One of the challenges for this experiment will be in hunting down the pre-1965 coins - good luck and happy hunting!

    Here is an interesting tidbit. Eggs also contain a lot of sulfur. If you eat eggs with a silver plated fork you will find that your fork has black tarnish on it when you are finished. You made a new chemical while eating your breakfast!

    Check out the ChemShorts October 2000 article on "The Science of Money" for other interesting trivia about coins and paper money (


    Kathleen Carrado Gregar, PhD, Argonne National Labs
    December 2007



    Brian Rohrig, "The captivating chemistry of coins", ChemMatters, ACS publication, April 2007, page 14 and
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