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Gold purity plays an important role in understanding the value and quality of gold ornaments. While accurate purity testing requires professional equipment and certified testing centres, there are a few simple methods that can be used at home to get a basic indication of whether gold may be pure or mixed with other metals. The methods explained below are intended for reference purposes only and can help you identify obvious signs of impurity, but they should not be considered a substitute for professional purity testing.
1. Magnet Test
- What to Do: Hold a magnet near the gold item.
- What to Check: Pure gold is non-magnetic, so if the item is attracted to the magnet, it likely contains other metals.
- Caution: This test only checks for magnetic metals like iron or nickel. Non-magnetic metals, like copper, won’t show a reaction either.
2. Float Test
- What to Do: Drop the gold item into a glass of water.
- What to Check: Pure gold is dense and will sink to the bottom. If it floats or hovers, it’s likely fake or mixed with lighter metals.
- Caution: This test isn’t definitive for distinguishing between pure and impure gold but can identify heavily adulterated gold.
3. Ceramic Scratch Test
- What to Do: Rub the gold item across an unglazed ceramic plate.
- What to Check: If it leaves a gold streak, it’s likely real gold. If it leaves a black mark, the gold may be fake or of low purity.
- Caution: Be gentle to avoid damaging your gold item.
4. Vinegar Test
- What to Do: Place a few drops of vinegar on the gold item or soak it in vinegar for a few minutes.
- What to Check: Pure gold won’t react to vinegar. If the metal changes color or tarnishes, it’s not pure gold.
- Caution: Use this test cautiously to avoid damaging other metals in the item.
5. Nitric Acid Test
- What to Do: Apply a small drop of nitric acid to the gold item.
- What to Check: Real gold won’t react to nitric acid. Fake or impure gold may turn green or black, indicating a reaction.
- Caution: Nitric acid is a strong chemical; use protective gear and perform this test outdoors or in a well-ventilated area.
6. BIS Hallmark Check
- What to Do: Check for the Bureau of Indian Standards (BIS) hallmark on the gold item, usually in a tiny, stamped symbol.
- What to Check: The hallmark certifies that the gold meets purity standards in India. Look for the BIS logo, purity in karats (e.g., 22K), and year of hallmarking.
- Caution: Be familiar with what the BIS hallmark looks like to ensure it’s authentic.
7. Gold Density Test
- What to Do: Weigh your gold item on a scale and then measure its volume by submerging it in water.
- What to Check: Pure gold has a density of around 19.3 g/cm³. You can calculate density by dividing the mass by the volume (water displacement).
- Caution: This test requires accurate measurement equipment to get precise results.
8. Touchstone Test
- What to Do: Use a touchstone, a smooth, dark-colored stone, to gently rub the gold item on its surface to leave a streak of the gold.
- What to Check: The gold’s color should appear as a rich, consistent yellow. If the color is off, such as being dull or lacking the natural shine of gold, it may indicate the presence of other metals or impurities. Skilled goldsmiths or jewelers often perform this test as it requires an expert eye to assess the exact shade and quality.
- Caution: This test requires practice and an experienced hand to accurately interpret the results. A poorly performed test can lead to misjudgment, so it’s best left to professionals.
- This method is often used by goldsmiths and jewelers, as the color of the gold line can help identify its purity when compared with known pure gold standards. The touchstone method is one of the most reliable traditional gold testing techniques.
Do it yourself: Take a piece of gold with known purity (e.g., 916 gold) and draw a straight line on a touchstone. Then draw a line with the gold you want to test. If both lines appear similar in color, the tested gold may have similar purity (916).
9. Touchstone Acid Reaction Test
- What to Do: After drawing a gold streak on the touchstone (as explained in the Touchstone Test above), place a small drop of the appropriate gold testing acid directly onto the existing gold line on the stone — not on the jewelry itself.
- What to Check: Observe how the gold line reacts: If the streak remains clear and unchanged, the gold may match the karat level of the acid used. If the streak fades, turns milky, greenish, or disappears, it indicates lower purity or the presence of other metals.
Different acids are designed for different karat levels (such as 18K or 22K), so the reaction depends on which testing acid is applied. - Caution: Acid testing requires proper acid solutions matched to different karat levels (e.g., 18K, 22K). Using the wrong acid can give misleading results. Acid is corrosive and must be handled carefully using protective gloves and eye protection. This test should ideally be performed by a trained jeweler or testing professional to avoid misinterpretation or damage.
*These home gold testing methods can provide a preliminary indication of gold purity. However, for accurate and reliable results, it is advisable to consult a professional jeweler or certified gold testing center.
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