Hardness is one of the oldest and most used methods for a jeweler to test for; keep in mind though this test can be incorrect, this is a test you will want to use in conjunction with other tests to help verify results. This test is often avoided in modern times, as there are less destructive/more accurate methods to testing stones. Since this test involves testing the structural hardness of the gem, this may involve scratching the gemstone. Scratching gemstones can have negative effects, such as weakening the gem itself. You’ll never want to use this test on a transparent stone, and used with caution on opaque stones.