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.
One way of telling if your jewelry is actually gold is by using a magnet. If your gold is magnetic, then there is iron or nickel inside of it. Pure gold is not attracted to magnetic fields, but if an enormous magnetic field is applied to gold, the gold will slightly move and then slightly repel it.
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.
Pure gold on its own cannot stick to a magnet. However, if you have an alloy of gold, then it could stick to a magnet. An example of a gold alloy that may stick to a magnet is gold with over 20% of its atoms replaced by iron. In very cold temperatures this alloy of gold may magnetize all on its own.
It is possible that an 18k gold piece sticks to a magnet. 18k or 18 karat means that a specific alloy contains 75% of pure gold and 25% other metals. Since pure gold is not magnetic, gold itself will not be responsible for the magnetism, but the metal alloyed may be.
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.
On the other hand, a piece may be gold plated, but it will not attach to a magnet because its core metal is non-magnetic.
Gold is a noble metal which is resistant to change by corrosion, oxidation, or acid. You can rub the gold-colored item on jeweller's black stone, which will leave an easily visible mark. The mark is tested by applying nitric acid and hydrochloric acid, which dissolves the mark of any item that is not gold.
Scientifically, gold is classed as diamagnetic, or magnetically inert. This means that it will not be attracted by a magnet, and cannot be turned into a magnet by applying an electrical current to it.
Place your jewelry on a table or hold it in your hand, pour some white vinegar on the metal directly (a dropper can also be used) if the metal of the jewelry changes its color, it is not pure gold and if it keeps shining then you have real gold in your hand.
Real gold bullion doesn't stick to magnets. Gold isn't magnetic, so it doesn't have the ability to be attracted to a magnet. However, a magnet can be used to test if gold is real or not. If the gold isn't attracted to the magnet, it's likely to be real gold.
Look for Stamps or Hallmarks in Your Gold Jewelry
Most real gold is stamped with a hallmark that indicates its purity, aka its karat. The karat is the unit used to measure the purity of gold. The higher the karat, the purer the gold. The most common karats you'll see are 10k, 14k, 18k, 22K, and 24k.
First off, if your "pure gold" is magnetic, then there is iron inside (or maybe nickel). In fact, this is one way to tell if jewelry is actually gold. If it's not attracted to a magnet then there is no iron - but it still might not be gold.
The Magnet Test
Since gold is not a magnetic metal, your jewelry should remain unaffected. If it sticks to the magnet, it's fake. (This test also works with silver, another non-magnetic precious metal.)
The reality is that gold alloy may contain other metals, making a chain magnetic even if it is not solid gold. Acid Test This test can be performed with an at-home kit, but the best option is to have this completed by your professional jeweler.
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.