Rub your gold against a jeweler's stone. Wipe it across the stone firmly enough to leave a mark. If the mark that you've left on the stone is solid and gold in color, then the piece is pure. If there is no line or only a faint one, then the piece is likely plated or not gold at all.
There are over seven tests you can choose from when testing gold at home. These include the magnifying glass test, hallmark test, skin test, float test, the magnet test, and acid test. You can also learn how to tell if gold is real with makeup, and how to test gold at home with makeup.
Apply a few drops of white vinegar to your gold jewelry. Real gold will not change color, but vinegar can cause fake gold items to react and change color.
Test With Nitric Acid
Make a mark deep enough to scratch through the top layer of gold. Carefully apply a drop of nitric acid to the mark, and determine if the mark turns green or milky. There will be no reaction if the jewelry is either gold or mostly gold.
Take an unglazed ceramic plate or piece of tile and scrape a piece of gold across its surface. Real gold will leave a gold mark or trail. Other metals will leave a black trail.
Rub your gold against a jeweler's stone.
Position a black jeweler's stone on a table. Hold your gold piece firmly in your hand. Wipe it across the stone firmly enough to leave a mark. If the mark that you've left on the stone is solid and gold in color, then the piece is pure.
Vinegar is very destructive, so when you apply the vinegar to a fake piece of gold, the vinegar will cause the jewelry to tarnish. Gold is a non-reactive metal, so real pieces of gold will not react to vinegar.
Scratch test.
If you cut deep enough that you expose underlying metal, you can assume that it is plated. If it appears to be made of a uniform composition throughout, then it is probably solid gold.
If it's real gold it will not stick to the magnet. (Fun fact: Real gold is not magnetic.) Fake gold, on the other hand, will stick to the magnet. If that necklace leaps to the magnet, your significant other has some explaining to do.
Goldmeter - real gold detector on the App Store.
Drop the gold into a jug of water to see if it sinks.
Real gold is a dense metal, so it falls directly to the bottom of the jug. Imitation gold is much lighter and floats. Real gold also doesn't rust or tarnish when wet, so if you see a discoloration, you probably have plated gold.
You will also need a small file or sandpaper to scratch the surface of the gold to be tested. To perform the test, first, scratch a small area of the gold with the file or sandpaper. This will remove the top layer of gold, exposing the inner layer. Next, apply a small drop of nitric acid to the scratched area.
The acid in the vinegar takes a couple of minutes to react with gold and other substances. Keep the vinegar sitting on your gold piece for at least 15 minutes, just to make sure it has gotten enough time to react. Watch the gold for color changes like black or green to see if it is fake.
Genuine gold will stand up to your attempt to conduct a nitric acid test at home. Make a tiny mark on the piece of gold to penetrate the surface. Drop a small amount of liquid nitric acid on that scratch and wait for a chemical reaction. Fake gold will immediately turn green where the acid is.
Both cause a chemical reaction that disintegrates the alloys in the jewelry over time. (Nearly all gold jewelry is alloyed, because pure gold is too soft on its own.) One study showed that when a 14K white gold ring was placed in common household bleach for 36 hours, the ring completely disintegrated!
The purer the gold, the stronger the acid required to dissolve it. Measured strengths of nitric acid are used to test for 14k and lower. Aqua regia, a mixture of one part nitric acid and three parts hydrochloric acid, is used to test higher karat purity through the process of comparison and elimination.
While brass is not bright yellow, it's more dull than gold. However, gold is much shinier causing its golden color. Impurities can cause the shiny metallic luster that is characteristic of gold to fade. The purity of the gold determines the shine of ornaments.