Make a small scratch on the gold and add a drop of bleach. If it changes color, your jewelry is not 100% pure 24K gold. Bleach can permanently damage gold jewelry. It can't tell you if your gold is fake, since most gold jewelry has other metals mixed in to give it strength.
We were reminded this earlier in February that many people aren't aware of the damage bleach and chlorine can cause to gold. 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.)
To safeguard the shine of your gold pieces of jewelry, stay away from abrasive chemicals that can be found in most homes, such as bleach and other cleaning items, which will rapidly make gold stain and conceivably break down on a physical level.
Test Gold Using the Float Test
Take a cup or glass, fill it up with water, now bring the gold that you want to test. Drop it into this filled glass. If the gold floats, it is surely not real but if the gold sinks to the end of the glass then it is pure gold. The real gold will sink due to being a heavy metal.
Chlorine turns gold karat jewelry black:
The effect upon chlorine on gold jewelry which is not pure 24K gold is to turn it black, due to a chemical reaction between the chlorine and various alloys which are mixed with gold to make it more durable.
Real gold does not react to most substances and common household bleach is one of them.
How to Test Gold With Vinegar. 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.
The Float Test
Place your gold piece into the water. If it's genuine gold, then it will immediately sink to the bottom of the cup. Pure gold is heavy due to its high density – 19.32 g/ ml. If your gold item floats or hovers above the cup's bottom – it's fake or plated gold.
The Acid Test
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.
While genuine gold is a stable metal and will not react to vinegar, fake gold can contain other metals that can react with vinegar, potentially causing a color change. The most commonly used alloys in fake gold are copper and zinc, both of which can react with the acetic acid in vinegar to produce a different color.
The acid in the vinegar can damage these delicate stones, leaving your jewelry looking less than its best. If you have gold jewelry with stones and want to clean it well, use mild soap and lukewarm water instead.
Some chemicals, especially chlorine and bleach, are corrosive to gold jewelry. So if you have noticed that your gold ring, bracelet, or anklet is showing considerable wear, bleach or chlorine damage may be at play.
It's not just chlorine that can damage your gold jewellery and diamonds; saltwater can damage them too. Salt causes erosion of soldered gold, silver or platinum elements. As a result, the precious metal may weaken meaning your jewellery could potentially break. The diamonds can also get blemished by salt.
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.
What to do: Hold the magnet up to the 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 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.
In order to distinguish gold from other base metals, the gold-containing item is rubbed on a black stone/surface which will leave a visible mark. Nitric Acid is then applied to the mark. If it easily dissolves, the item is not Gold. If the mark remains, Aqua Regia (Nitric Acid and Hydrochloric Acid) is then applied.
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.
Basically, gold won't react to nitric acid, but all other metals will turn greenish. Don't douse your jewelry in the acid—just put it in a stainless-steel dish and use a dropper to drop or Q-tip to test a tiny section. If your jewel doesn't react to the nitric acid, you have a real gold piece (14k or higher).
Chlorine is gold's worst enemy: with repeated exposure, chlorine will weaken your gold jewelry's structure and eventually lead to it breaking. Make sure to take your jewelry off before getting in a pool or spa. Cover or remove while cleaning: household cleaners with acids or abrasives will damage your jewelry's finish.
In conclusion, testing gold with alcohol is a simple and easy method that can be used to determine if an item is made of solid gold or if it is gold-plated. However, it is important to remember that this method is not as accurate as acid testing and should only be used as a preliminary test.