How to Test if Gold is Real

Gold has been highly prized throughout history, and with the steady increase in gold prices, the problem of fake gold has also risen. Unfortunately, victims of fake gold are often lured by unrealistic deals that involve counterfeits of different qualities. The good news is that real gold can be easily tested and there are many ways to do it.

Gold testing is broadly categorized into two testing methods: non-destructive and destructive. We share the details of each testing method and the context behind why they are used today.

Non-destructive Ways to Test if Gold is Real

When retail gold investors or buyers want to test gold, they want to ascertain if the gold is real without damaging the gold item. Non-destructive testing methods for authenticating gold verify the authenticity and purity of gold without damaging the item being tested.

Below are some non-destructive methods for gold testing.

Density Test or Specific Gravity Test

One of the easiest ways to test for authentic gold is to perform a density or specific gravity test. While both tests are often mistaken for the same, they are not. Although density and specific gravity describe mass, they are not identical.

Density refers to the amount of mass contained within a given volume and is typically expressed in units such as grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³). For example, gold has a density of 19.32 g/cm³.

Specific gravity, on the other hand, is a dimensionless value that compares the density of a substance to that of a reference material, usually water, which has a density of 1 g/cm³ at 4°C. Since gold’s density is 19.32 times greater than that of water, its specific gravity is also 19.32.

Therefore, density is a unit of measurement, while specific gravity is a ratio comparing densities.

A simple gold testing kit can include a digital weighing scale and caliper. You can perform a simple gold density test by weighing your gold bullion bar or coin on the weighing scale and measuring the sample’s dimensions using the digital caliper. Major gold refineries often publish the reference dimensions of gold bullion coins and bars on their websites, which can be checked against with your digital caliper readings.

However, digital caliper measurements may not be feasible for odd-shaped items like gold jewelry and pendants. A specific gravity test would be more suitable for such items. You can find the details of performing a specific gravity test here.

Sound Test

The sound test, also known as the "ping test," is a simple way to evaluate whether a gold item is real by striking it gently and listening to the sound it makes. Pure gold produces a distinct sound that is different from other metals.

To perform the test, the gold item, typically a coin or bar, is gently tapped with another object, such as another coin, or suspended and struck lightly to allow it to vibrate freely.

Genuine gold, especially of higher purity, produces a distinct ringing sound or "ping" dissimilar to other metals. The resonance occurs due to gold's unique density and material properties, influencing its acoustic vibrations.

However, this test is limited in reliability as it requires a trained ear to differentiate sounds and may not work well with items of lower purity, smaller, or irregularly shaped. It is often used as a preliminary check rather than a definitive method for verifying gold.

Magnet Test

Using magnets to test gold is a simple and non-destructive method to help identify counterfeit gold. Such tests use magnetic susceptibility to distinguish between different elements.

Pure gold is diamagnetic, meaning magnets weakly repel it. In other words, gold does not attract magnets and cannot be magnetized.

However, the right type of magnet must be used to perform the magnet test for gold properly. Typical fridge magnets are too weak to react to gold’s diamagnetism. Rather, stronger neodymium magnets are required to perform a magnet test effectively.

If outright magnetic attraction is not detected when testing gold with a strong magnet, a slide test is usually performed. Being diamagnetic, weak magnetism should be observed during a slide test with a neodymium magnet.

With the gold sample placed at a 45-degree angle to a surface, place the magnet at the top, allowing it to slide down. If the sample is non-magnetic, the magnet will slide down quickly. However, if it is real gold, the magnet will slide down slowly.

However, a magnetic slide test may not be entirely reliable if you cannot objectively distinguish between the speed of the slide should a different diamagnetic element be used in the counterfeit gold.

Compared to advanced testing methods like ultrasound and X-ray fluorescence (XRF), the magnet test is a quick and inexpensive preliminary check but lacks precision. It should be treated as a convenient tool for casual verification, particularly for identifying obvious counterfeits. However, it should always be supplemented with more advanced techniques for accurate authentication.

Ultrasound Test

Testing gold with ultrasound involves using sound waves to detect inconsistencies within the item, making it a reliable and non-destructive method for verifying authenticity. The principle is based on how sound waves travel through materials with specific densities, also known as celerity.

Since genuine gold has unique acoustic properties due to its density and atomic structure, the way sound travels through it differs significantly from counterfeit materials like tungsten or other alloys.

Ultrasound devices for testing gold range from basic to industrial-grade models, catering to different needs and budgets. Basic ultrasonic thickness gauges, commonly sold on online marketplaces, primarily measure the thickness of the tested gold sample.

Higher-end industrial-grade ultrasound devices are often geared toward flaw detection and have a rugged design, larger VGA displays, stronger receivers, and the ability to display sound waveforms and patterns for analysis. This range of ultrasound testers is more suited for vault operators or precious metals authentication laboratories that need to test large gold and silver bars regularly.

Regardless, these devices use probes or pulsers to send sound waves through the gold and calculate the time it takes for the waves to return. Since solid gold has a celerity of approximately 3,240 meters per second (m/s), the thickness of the tested sample can be calculated based on the time it takes for the sound waves to return to the ultrasound probe.

Ultrasound tests are highly reliable for detecting counterfeit gold since they penetrate the sample medium to detect potential gold plating, gold filled with tungsten cores and even potential irregularities like hidden voids. However, ultrasound may be less effective when testing small, thin or irregularly shaped gold products such as gold jewelry or small gold coins and bars.

Electrical Conductivity Test

Electrical conductivity measurement tests (or ECM tests) are a non-destructive method used to verify the authenticity of gold by analyzing how easily electric current flows through the material. The test works on the principle that different metals have unique levels of electrical conductivity determined by their atomic structure and electron mobility.

Gold is an excellent conductor of electricity, with an electrical conductivity of approximately 44.7 MS/m (megasiemens per meter) at room temperature. This high value distinguishes gold from most common counterfeit materials with different conductivity values, such as tungsten or alloys.

To perform the test, a specialized device, also known as an ECM tester, measures the material's resistance to electrical current and calculates its conductivity. Genuine pure gold exhibits consistent conductivity across its surface, while counterfeit materials or impurities cause deviations.

The Sigma Analytics Precious Metal Verifier (PMV) is a common ECM tester frequently used by bullion dealers, jewelers, and pawnbrokers. It is known for its user-friendliness and swift response (often less than 1 second). The device has two testing methods – a circular onboard sensor for smaller samples and several testing wands for larger samples.

The PMV tester conveniently comes with many preset testing profiles for precious metals with varying fineness. However, the purity or alloy composition of the test sample must be known before the appropriate test profile can be selected for an accurate test.

The Precious Metal Verifier's measurement results can be influenced by factors such as the coin's temperature, stamping relief, and alloy composition. The device accounts for temperature variations and generally has a minimal impact. Under normal conditions, this is unlikely to be a concern. However, significant temperature effects may occur if the sample has been exposed to extreme heat, such as being left in a hot car or extreme cold for an extended period.

Additionally, ECM tests are unsuitable for thick gold bars like the LBMA 400 troy-ounce gold bar, given its penetration depth of approximately 1.5 mm to 3 mm only, depending on the sample’s purity. Signal penetration is deeper with higher metal resistivity.

An advantage of an electrical conductivity measurement test over an ultrasound test is that the former works even for blister-packed gold bars or coins, penetrating through the plastic packaging to produce the test result. An ultrasound test cannot produce reliable results in this scenario as it requires direct contact with the test sample to work.

X-ray Fluorescence Test

X-Ray Fluorescence (XRF) is a non-destructive analytical technique used to determine the elemental composition of materials. It works based on the principle of X-ray excitation, where atoms within a material become excited when exposed to high-energy X-rays.

This excitation causes the inner-shell electrons of the atoms to be ejected. Outer-shell electrons then fill the vacancies, and during this transition, the atoms emit secondary X-rays (fluorescence). The energy and wavelength of these fluorescent X-rays are characteristic of specific elements, like fingerprints, allowing their identification.

X-ray testing may not be a commonly available retail method to test gold. XRF analyzers are costly and require a licensed operator because they emit radiation. However, well-established precious metals dealers and vault operators are more likely to offer X-ray tests for gold.

One of the benefits of an X-ray test is that it can detect the surface composition of odd-shaped and thin gold items such as gold jewelry and small gold bullion. If the item is pure gold, the XRF analyzer’s display will usually show ‘AU 99.99%,’ signifying that it is gold (AU being gold’s periodic table symbol) and its respective fineness.

X-ray test results are usually produced within a few seconds, showing the elemental composition of the tested sample.

However, X-ray tests do have some limitations. Given XRF’s limited penetration depth, which makes it more suitable for surface analysis, it is unsuitable for testing thick samples. Therefore, an X-ray test may not be able to detect fake gold with thick gold plating.

Like ultrasound, an X-ray test also requires direct contact with the test sample as it relies on the physical interaction between the sample’s emitted X-rays and the XRF analyzer. Gold bullion sealed in plastic blister packs will prevent accurate X-ray test readings. Misleading readings can also occur due to irregular surfaces or the presence of surface impurities or coatings.

Despite its limitations, an X-ray test is unique because it is the only non-destructive testing method for gold that displays the surface’s elemental composition.

Destructive Testing Methods

Besides non-destructive gold testing methods, the precious metals industry also uses destructive testing methods, like an acid test or fire assay, if required. However, these tests are destructive as they damage the sample partially or completely.

Acid Test

An acid test can determine the purity of gold and potentially detect fake gold. It involves rubbing the gold item against a touchstone to leave a streak. Then, a few drops of nitric acid solutions of varying concentrations were applied to the gold streak. Each solution corresponds to a specific karat level (e.g., 10K, 14K, 18K, or 22K). If the streak dissolves, the gold content is lower than the karat of the acid applied. If it remains intact, the gold is at least as pure as the karat level of the acid.

However, the acid test has limitations. While it is effective for identifying the approximate purity of gold, it is mainly a surface test since one cannot scrape too much of the gold piece without substantially damaging it. Therefore, an acid test may be ineffective if the sample has thicker plated gold.

Fire Assay

Fire assay is often considered as a highly accurate method used to determine the gold content in a sample. The process involves melting the gold sample in a furnace at high temperatures with a mixture of lead, fluxes, and other chemicals to separate gold from impurities.

The molten lead absorbs the precious metals, while the impurities are trapped in a slag layer. The lead is then oxidized and removed, leaving the precious metal, which is weighed and further refined to isolate the gold content. This method is considered the industry standard for gold purity analysis due to its reliability and precision.

Fire assay is typically used in circumstances where precise gold content measurement is critical, such as refining, certification, and high-value transactions. While it is the most accurate method, it has certain drawbacks. The process is destructive, as the sample is completely consumed during testing and requires handling hazardous flux materials in the test laboratory. Additionally, a fire assay is time-consuming and requires specialized equipment and skilled operators, making it more expensive than the quicker non-destructive testing methods for gold.

However, fire assays are used when precision outweighs the need to preserve the sample, such as in refining or cases requiring absolute certainty about gold purity.

Word of Caution For Gold Testing

As tungsten has an almost identical density to gold (19.25 g/cm³ versus gold’s density of 19.3 g/cm³), it is commonly used in fake gold. Therefore, there is a high chance that novices may not detect a tungsten-core gold-plated bar or coin if they only perform a density test. However, tungsten can be easily detected if another test, such as an electrical conductivity or ultrasound test, is also used.

Herein is an important principle when authenticating gold: never rely on only one testing method. Always use at least two or three methods to achieve the highest certainty of authenticity.

The wisdom of using at least two testing methods is rooted in the scientific understanding of elements, that no two distinct elements have identical properties. Using tungsten as an example, other properties of tungsten show a big difference compared to gold.

For example, gold’s celerity (speed of sound travelling through a medium) is 3240 m/s, while tungsten’s celerity is 5220 m/s. The electrical conductivity of gold and tungsten is 44.7 MS/m and 18.52 MS/m, respectively.

Therefore, conducting a second or third test is an excellent way to identify the best-produced counterfeit gold bars or coins. They also guard against fake gold products that are optimized for a specific type of test. For instance, a counterfeiter may produce gold-plated copper bars to fool a pawnbroker, knowing that they predominantly rely on electrical conductivity tests for testing gold. However, if the pawnbroker also weighs or checks the dimensions of the fake gold coin or bar, they can easily detect discrepancies in the sample’s properties.

How The Safe House Authenticate Gold

Since its inception in 2014, The Safe House vault in Singapore has many years of experience in using non-destructive testing methods to authenticate gold bullion and other precious metals. Our gold testing laboratory is fully equipped with equipment for ultrasound, electrical conductivity, density, magnetism and X-ray tests.

Precious metals transferred by clients for storage in our vault are required to be authenticated before being accepted for storage. Tests are conducted under CCTV surveillance and results are transparently made known to clients.

Clients with appointments to visit The Safe House are also able to witness how gold is tested in our laboratory, gaining an understanding of the testing process through our experienced vault personnel.

Contact The Safe House if You Have Questions

Contact us today if you are planning to transfer gold for storage with us in Singapore and have questions regarding the transfer or testing process. Our experienced staff look forward to assisting you, ensuring that your bullion transfer is smooth and easy.