How to Tell if a Metal is Pure Silver?

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Silver is a soft, lustrous, pliable, white metallic transition element with a symbol of Ag, melting point of 961.93 degrees centigrade and an atomic number of 47. Pure silver is too soft to be worn as jewelry, so it is alloyed with harder metals for that purpose. Silver tarnishes when exposed to oxygen in air, so it is often coated with a less-reactive metal, like rhodium, for aesthetic purposes. Inductively coupled plasma optical emissions spectroscopy is the preferred method for elemental analysis of pure silver. However, for most practical uses, simply determining the presence of silver in an object is sufficient. A simpler, less-destructive nitric acid test is used for this purpose and in home-testing kits.

Things You'll Need

  • Nitric acid
  • Silver jewelry
  • Metal file
  • Napkins
  • Water
  • Scratch the silver jewelry with the metal file. Choose an inconspicuous location on the piece of jewelry to minimize the visibility of any damage resulting from the test. Ensure that the scratch is deep enough to expose the inner layers of the metal as jewelry can be silver-plated. Silver jewelry can also be covered with a layer of inert metal.

  • Place a drop of nitric acid on the scratched area. Silver is often used as a top layer over less-expensive metals to increase the durability of jewelry while keeping the cost down. The scratched area should be deep enough for the nitric acid to reach the inner layers to prevent false-positive results.

  • Observe the color of the acid on the metal. A creamy color indicates the presence of 90 percent to 100 percent silver. An ashy-gray color indicates sufficient purity to qualify as sterling silver. Any other color indicates a lower level of purity. Bubbling green acid indicates the presence of copper and means that the item has been plated with silver.

  • Rinse the nitric acid from the metal to stop the reaction.

  • Pat the piece of jewelry dry.

Tips & Warnings

  • Take appropriate safety precautions, such as wearing protective eyewear and gloves when handling nitric acid. If you are using a testing kit, follow the manufacturer's directions. Make sure you have a tap or shower nearby to quickly rinse off accidental spills.

References

  • Photo Credit Ryan McVay/Photodisc/Getty Images
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