A magnet attracts gold, indicating it's fake. This can be confirmed by testing it at a gold jeweler. A few drops of white vinegar can tarnish fake gold. The chemical Nitric Acid Test, which should never be performed at home, can cause fake gold to foam, turn green, and tarnish in gold jewelers. An XRF Spectrometer (X-Ray Fluorescence Device), available at jewelers, can be used to test gold content and various karat values using karat acids and accurately determine its value. An Ultrasonic Density Meter can also be used to detect fake tungsten-filled gold bars. Buy gold from reputable jewelers and goldsmiths.