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How to Test 10K Gold

Ten-karat gold is an alloy that contains no less than 10/24 (41.67 percent) pure gold by weight. In the U.S., 10K gold must bear a stamp or imprint of the letters "10K." Items of less than 10K purity need not be marked.

To determine the purity of gold, jewelers and gold buyers use a test kit to compare an unknown to gold of known purity. This kit contains a test stone, bottles of nitric acid and "aqua regia" (75 percent hydrochloric and 25 percent nitric acid) and needle-shaped samples of standard gold alloys.

Things You'll Need

Metal file
Gold test kit
Magnifying glass

Instructions

- 1
  Clean soil and grease from the object to be tested. Use a metal file to make a small scratch in the surface.
- 2
  Place a single drop of nitric acid on the scratch and observe the color. Bright green means the item is gold-plated or gold-filled on copper, brass or another base metal. Pink indicates gold-plating or gold-filled on silver. Other colors indicate gold alloys, and should be compared to a standard of known purity.
- 3
  Rub the clean spot on the test stone from the test kit. Rub the test kit's 10K sample on the test stone near the mark. Apply nitric acid to both marks at the same time. Examine the two marks with a magnifying glass and compare the colors. If they are the same, the unknown item is also 10K. More pure gold will be lighter than 10K gold.

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