How to Know Purity of Silver Bars

Examine the silver bar for a stamp indicating its purity, using the magnifying glass if necessary. By law, sterling silver is required to be stamped with the purity. A marking of 0.900 means the silver is 90 percent pure, while 0.925 is 92.5 percent pure. Most investment-grade silver bars are 0.999, or 99.9 percent, pure silver and 0.01 percent copper.

Run the magnet over the silver bar. Genuine silver isn't magnetic, so this test can detect a fraudulent metal such as nickel.

Use the file to scratch or scuff a small area on the bottom of the bar, where it will be less noticeable. It doesn't need to be big, just enough to break through any electroplating or other coating used to fool people into thinking it is silver. If the metal all looks the same and passed the magnet test, it is likely silver.

Apply a drop of the nitric acid testing solution to the scuffed area and see what color it changes to. Dark red indicates the silver is between 90 and 100 percent pure. A light red or creamy, brownish tint means the silver is 80 to 90 percent pure, while green indicates it's about 65 to 80 percent pure.