Testing raw gold starts with a few simple checks you can do at home, then scales up to more precise methods depending on how sure you need to be. Whether you pulled a glittering nugget from a stream or inherited a piece you’re not sure about, the right combination of tests can tell you if it’s real gold, how pure it is, and whether it’s worth taking to a professional.
The Streak Test: Your First Field Check
The fastest way to separate gold from lookalikes is a streak test. All you need is an unglazed ceramic tile (the back of a porcelain plate works in a pinch). Drag your specimen firmly across the surface and look at the color of the mark it leaves behind.
Real gold always leaves a brilliant golden-yellow streak. Pyrite, the most common impostor, leaves a greenish-black or brownish-black mark. This single test eliminates most fool’s gold on the spot. The streak color is far more reliable than the surface appearance, since pyrite can look convincingly gold-colored in certain lighting. If the streak is dark, you don’t have gold.
The Magnet Test
Gold is not magnetic. Hold a strong neodymium magnet (the small, powerful kind sold at hardware stores) directly against your specimen. If it sticks, the piece contains iron, nickel, or another magnetic metal and is not pure gold. If it’s slightly attracted but doesn’t cling, there may be magnetic impurities mixed in.
This test is useful but not definitive on its own. Plenty of non-gold materials are also non-magnetic. Tungsten, one of the most common materials used to fake gold bars and coins, won’t stick to a simple magnet either, though it does have different magnetic susceptibility than gold. The magnet test is best used to quickly rule out obvious fakes rather than confirm authenticity.
Testing Density With Water
Gold is extraordinarily dense: 19.32 grams per cubic centimeter. That’s about twice as heavy as lead and nearly twenty times heavier than water. Very few materials match this density, which makes a water displacement test one of the most reliable home methods for identifying gold.
Here’s how to do it. First, weigh your specimen on a scale accurate to at least 0.1 grams and record the weight. Then fill a graduated cylinder or narrow container with water and note the water level. Drop the specimen in and record the new water level. The difference between the two water levels is the volume of your specimen in milliliters (which equals cubic centimeters).
Divide the weight by the volume. If the result is close to 19.3, you likely have pure or near-pure gold. A reading around 15 to 17 suggests gold alloyed with lighter metals, which is common in naturally occurring gold that contains some silver. A reading significantly below 14 points to a different mineral entirely or heavy plating over a lighter core. Pyrite, for comparison, has a density of about 5, so it fails this test dramatically.
Accuracy depends on your measurements, so use the most precise scale and narrowest container you can find. Small specimens are harder to measure because the volume displacement is tiny, and rounding errors get amplified.
The Acid Scratch Test
Acid testing is the standard method jewelers use to estimate gold purity, and you can buy testing kits from jewelry supply companies for around $15 to $40. A basic kit includes a black touchstone (a type of fine-grained stone), several bottles of acid solution calibrated to different karat levels, and sometimes reference needles of known purity.
To test, scratch your gold specimen across the touchstone to leave a visible streak. Then apply a drop of the lowest-karat acid solution (typically 10K) to the streak. If the streak dissolves, the gold content is below that karat level. If it remains, move up to the next acid (14K, 18K, 22K) until you find the solution that dissolves the streak. The highest acid that fails to dissolve the streak tells you the approximate purity. Pure gold does not react to nitric acid at all.
This method requires careful safety precautions. The Gemological Institute of America recommends working in a well-ventilated area and wearing protective gloves and safety goggles. Keep a beaker of baking soda dissolved in water nearby to neutralize acid spills and to clean your touchstone between tests. After each test, place the touchstone in the baking soda solution, then rinse it in clean water. Between uses, sand the touchstone with 320-grit abrasive paper to remove residual metal, neutralize again, and dry before storing.
Electronic Gold Testers
Electronic testers measure the electrical conductivity of your specimen using a technology called inductive eddy current measurement. You press the probe against the surface, and the device reads the conductivity pattern and compares it against known values for different gold purities. These devices range from about $100 for basic models to over $1,000 for professional-grade units.
The advantage is speed and simplicity: you get a reading in seconds without chemicals or calculations. Electronic testers are particularly good at catching tungsten counterfeits, which fool both the magnet test and the density test (tungsten’s density of 19.25 is almost identical to gold’s 19.32) but have very different electrical properties.
The limitation is that electronic testers measure the surface and near-surface only. A thick gold plating over a base metal can sometimes fool cheaper models. For this reason, manufacturers recommend combining electronic testing with at least one other method, such as density testing, for a comprehensive check.
Understanding Gold Purity
Raw gold from nature is rarely pure. Most placer gold (the kind found in rivers and streams) runs between 70% and 95% gold, with the remainder being mostly silver and trace amounts of copper or other metals. The purity of your specimen determines its value, and two scales are used to express it.
The karat system divides gold into 24 parts. 24K is 99.99% pure gold. 22K is 91.67% gold. 18K is 75% gold. 14K is 58.3%, and 10K, the minimum legal threshold for calling something “gold” in the United States, is 41.7%. The fineness system expresses the same thing in parts per thousand: 999.9 fineness equals 24K, 916.7 equals 22K, and so on.
For raw, unrefined gold, your home tests can give you a rough bracket of purity. The density test narrows the range based on weight, and the acid test identifies the approximate karat. But for an exact figure, especially if you plan to sell, you’ll need a professional assay.
Professional Fire Assaying
Fire assaying is the most reliable method for determining the precise gold content of a sample. It has been the standard in mining and refining for centuries, and the basic principles haven’t changed since they were first documented in the 1500s.
The process works by mixing a small weighed sample of your gold with chemicals that lower its melting point, then heating everything in a furnace. The non-precious material separates into a glass-like slag that gets removed, leaving behind a lead button that contains the gold and silver. That button is then heated again in a special ceramic cup called a cupel, which absorbs the lead, leaving only a tiny bead of precious metal.
To separate the gold from any silver in that bead, the assayer dissolves the silver in nitric acid (gold doesn’t react to it). What’s left is weighed, and the difference tells you exactly how much gold and how much silver were in your original sample.
Fire assaying typically costs $25 to $75 per sample at commercial labs and is the method refiners use before making you an offer. If you have a significant amount of raw gold, this small investment gives you the precise numbers you need to negotiate a fair price. Many assay offices are attached to refineries, and some will credit the assay fee toward the cost of refining if you proceed with them.
Combining Tests for Confidence
No single test is foolproof. The streak test eliminates pyrite but doesn’t tell you purity. The magnet test catches iron-filled fakes but misses tungsten. The density test catches most counterfeits but can be fooled by tungsten. The acid test estimates purity but only checks the surface. Electronic testers are fast but have depth limitations.
For a specimen you pulled from the ground, start with the streak test and magnet test to confirm it’s actually gold. Then do a density test to estimate purity. If the numbers look promising, an acid test or electronic tester can refine your estimate. And if you plan to sell, send a sample out for fire assaying to get a definitive answer. Stacking two or three methods together gives you a level of certainty that any single test can’t match.