A magnet is all you need to determine if your precious metal piece is brass or gold. Because brass has iron, the magnet sticks due to it iron being a magnetic metal. Gold, on the other hand, is pure and will not move one inch under the influence of any strong magnet.
Apply acid to the metal.
Brass will react with acids and gold will not. If you see bubbling or discoloration where the acid is applied, your piece is brass. If there is no change after applying the acid, you have gold.
Solid brass is not magnetic. If the magnet sticks, the item is usually steel or cast iron, with a brass plating. If the magnet does not stick, you can test further by scratching a hidden area with a sharp tool. If you see a shiny yellow scratch, the item is likely solid brass.
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.
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.
How to Test If Gold Is Real with a Lighter. The first test is also the easiest test: try to burn your gold. If it's real gold, it will get brighter as you apply the flame but it won't actually catch fire and burn. If your gold piece starts to smoke or gets darker, you likely have imitation gold.
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 & Stone. Perhaps the most commonly used test for gold testing over the counter is the scratch test. This process allows you to visually identify if a piece, when scratched on the stone, holds utilizing the 10K, 14K, 18K and 22K acid.
Look for a Letter Mark
If the item of jewelry has the letters GP, GF, or GEP stamped on it, these indicate that it is not made of real gold. GP means it is gold plated, GF means it is gold filled, and GEP means it is gold electroplate. That is, the jewelry is made of some other metal with a thin layer of gold on top.
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.
Certain metals in their natural states such as aluminium, copper, brass, lead gold, and silver don't attract magnets due to the fact they are weak metals. However, properties including iron and steel can be added to these metals in order to make them magnetic.
As with testing precious metals, a magnet will not tell you if an item is made of copper / brass / bronze, but it will tell you if it isn't.
Finally, because brass is so inexpensive it really doesn't hold any value that will make it worth anything in the future.
Pinchbeck is a form of brass, an alloy of copper and zinc mixed in proportions so that it closely resembles gold in appearance.
Gold-plated brass will tarnish over time, but it will take longer than if the piece is made of pure brass. The gold plating protects the brass beneath it from tarnishing, but eventually, the gold itself will begin to fade, leaving the base metal susceptible to tarnishing.
The simplest test for you would be a weight test; gold is much heavier than brass, well over twice as heavy, 19.3 g/cm for gold vs. the vicinity of 8.5 g/cm for brass, depending on composition.
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. Gold will not react to the nitric acid.
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.
The most common mineral mistaken for gold is pyrite. Chalcopyrite may also appear gold-like, and weathered mica can mimic gold as well. Compared to actual gold, these minerals will flake, powder, or crumble when poked with a metal point, whereas gold will gouge or indent like soft lead.
One of the simplest ways to test gold at home is the Float Test. All you need is a cup (or bowl) of water and your gold item. Place your gold piece into the water. If it's genuine gold, then it will immediately sink to the bottom of the cup.
Neodymium rare earth magnets for testing gold and silver purity.
Be sure to use plain white toothpaste; avoid any with colored stripes or other added ingredients. Rub the toothpaste onto the gold for about 30 seconds. You should see a black streak begin to form.
Keep in mind that vinegar dissolves not just the patina or stains on your brass surface. You may not notice it, but it can dissolve brass itself, depending on its potency. So, when you polish brass with vinegar, be careful not to scrub or buff too hard.
This is due to other environmental, chemical and biological factors. On the Coast, we have a lot of salt, and therefore chlorine, in the atmosphere. Elements such as sulphur and chlorine react with the other metals in the gold jewelry, causing it to corrode and turn black, thus blackening the skin underneath.
Bleach can't tell you if your gold is fake.
Instead, it can only tell you if it's 100% pure 24K gold, since pure gold doesn't react with bleach. But in many cases, other metals are mixed into gold to give it strength or change its color—like with rose or white gold—and even yellow gold isn't always pure.