Spot fake gold with the lemon method Put a small drop of lemon juice onto the scratch using the liquid dropper. Observe any color changes in your gold. Real gold will retain its lustrous sheen and stunning yellow color. Fake or impure gold will likely darken or show discoloration.
Lemon Juice
Lemon is naturally acidic, which helps remove the oxide layer on the jewelry easily. Mix equal parts of water and lemon juice. Soak the jewelry in this solution for 10 to 15 minutes. Gently scrub the jewelry with a rough cloth or toothbrush.
Get a ceramic plate and scratch the gold piece you're testing against it. If the gold is real, you should see a yellowish streak on the plate. If it's fake, you'll see a dark streak.
You can also fill a cup or glass with white vinegar, and drop your gold in it, let it soak for 5-8 minutes, take it out and rinse with water. If the metal has changed its color even slightly, then the gold is not pure but if it keeps shining, then the gold is pure.
If your gold piece turns black or green when the vinegar is on it, or if it starts to smoke or fizzle at all when the vinegar touches it, it is most likely not real gold. If your gold piece does not change colors and does not fizzle or react to the vinegar in any way, it is probably real.
Acid test.
An acid test can reveal the karat of solid gold jewelry, but it can also show whether jewelry is solid gold or gold-plated. With an acid test, a small sample of the jewelry is removed and exposed to acid to induce a color change. The resulting colors indicate which type of metal the jewelry is made of.
Heat your gold jewelry with the lighter.
Apply the flame to the jewelry for about a minute or 60 seconds. Watch it closely for any changes in color. Fake gold will get darker, while pure gold will do the opposite: it will get brighter the hotter it gets.
The Nitric Acid Test
Gold is a noble metal which means its resistant to corrosion, oxidation and acid. To perform this test, rub your gold on a black stone to leave a visible mark. Then apply nitric acid to the mark. The acid will dissolve any base metals that aren't real gold.
Lemon juice is incredibly acidic. While this might be okay for sturdier jewelry, for anything soft or plated, you're asking for trouble. It's too abrasive for your delicate jewelry and you'll end up with chips, scratches, and discoloration. Don't weaken your jewelry with lemon juice.
Toothpaste is abrasive and has a hardness of around 3/4 on the Mohs Scale of Hardness. Metals such as gold and silver are softer, so toothpaste can actually scratch damage your gold and silver jewellery. Not to mention, the chemicals in the flavour oils used in toothpaste are corrosive to metal.
Lemon juice has no effect on solid gold. However, it is too abrasive for gold-plated jewelry. It may also damage lower gold karats, which contain significant amounts of metals for durability. Prolonged exposure can cause discoloration or severe damage.
Because gold is a soft metal, it is easily scratched even with a light abrasive like baking soda.
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.
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. Observe the reaction, and compare the results to the chart provided in the kit.
Float Test
It is one of the easiest ways of checking gold purity at home. If you put the gold jewellery in a bucket of water and it sinks, then it is made of pure gold. Pure gold is dense and therefore does not float while other metals would float or hover over water.
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. Gold-over-sterling silver will become milky in appearance. Gold will not react to the nitric acid.
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.
Check if your gold is real by performing the magnet test. Real gold will not attract a magnet. To test if 18k gold is real, hold it next to a magnet. If the magnet sticks to your jewelry, then it does not have a high percentage of gold but is made up of other, more magnetic metals.