Secrets of Gold Density: The Key to Understanding Its Value
Gold has always served as a safe-haven asset, offering a way to protect capital from inflation, financial crises, and currency market instability. It is easily acquired through banks, authorized dealers, or at auctions, attracting both investors opting for bars and coins, and numismatists searching for rare specimens.
However, with the increasing popularity of gold, the likelihood of encountering fakes also grows. This is especially true for antique items, where hallmarks may be absent, and distinguishing a genuine item from a fake by 'eye' is not always possible even for an experienced jeweler. Fortunately, there's a fairly simple way to perform a quick check at home: you just need to know the metal's density and be able to calculate it yourself.
What are Specific Gravity and Density of Gold?
Density is a physical quantity that expresses the ratio of an object's mass to the volume it occupies. For 999 pure gold, this indicator is extremely high, at 19.3 g/cm³. This is almost twice as much as lead and three times as much as iron.
To better understand this figure, imagine a cube with sides of 3.7 cm – about the size of a matchbox. If such a cube were made of gold, its weight would be a full kilogram. A standard bank bar according to GOST 28058 usually weighs between 11 and 13 kg. This means that a briefcase filled with gold bars, as often shown in Hollywood movies, would weigh about 250 kg, making it not just difficult to carry, but practically impossible to lift.
In the jewelry industry, the concepts of specific gravity and density are traditionally equated, simplifying their use in everyday practice.
The Relationship Between Gold Density and Purity
The density of gold directly depends on its fineness (purity), which indicates the percentage of pure precious metal in the alloy and the quantity of additives (ligature). The higher the fineness, the more pure gold, and consequently, the higher the density.
| Purity | Density (g/cm3) |
| 999 | 19.32 |
| 750 | 14.8-15.9 |
| 585 | 13.2-14.7 |
| 375 | 12.1-12.5 |
It's worth noting that the density of 585 purity gold can vary within the specified range, as this alloy contains 58.5% pure gold and 41.5% ligature metals such as copper and silver, whose densities are significantly lower. This circumstance somewhat complicates the identification of fakes for 585 purity, but does not make it impossible.
Knowing these characteristics, one can immediately draw conclusions about potential fakes. For example, the density of lead (11.34 g/cm³) is very close to that of 375 purity gold. With a sufficiently thick gold plating, only a jeweler would be able to distinguish such a fake. Tungsten (19.3 g/cm³) is close in density to 999 purity gold, but it is significantly harder, which can also be used for verification. As for hollow or so-called 'blown' items, even if they are made of real gold, their overall density will be significantly lower, according to jewelers' calculations, up to 5 g/cm³.
Practical Determination of Gold Density
There is a fairly simple and reliable way to check the authenticity of gold items, especially antique ones, at home. For this, you will need scales accurate to 0.1 gram, a container of water, and strong thread.
- Weigh the item itself and record its mass.
- Place a not-fully-filled container of water on the scales.
- Zero the scale.
- Carefully lower the item into the water on a thread so that it is fully submerged but does not touch the bottom or sides.
- Record the new scale reading. This value will be equal to the volume of displaced water in cubic centimeters, since the density of water is 1 g/cm³.
Now, substitute the obtained data into the density formula:
P = m/V
where P is density, m is the dry weight of the item, V is the volume (equal to the weight of the item in water).
Suppose you are checking an investment gold coin weighing 31.1 g (which corresponds to a troy ounce). If the weight of the displaced water is 1.61 g, the calculation will be as follows: P = 31.1 / 1.61 = 19.32 g/cm³. This result indicates that you have a 999 purity coin.
An interesting historical fact: Archimedes' famous "Eureka!" and the method of measuring the volume of bodies by displaced liquid arose when the scientist was trying to determine whether the crown of the Syracusan king was truly made of pure gold. Archimedes compared the volume of the crown with the volume of a gold bar of similar weight. It turned out that the volume of the crown was larger, which meant that part of the gold had been replaced with lighter silver.
Comparing Gold Density with Other Metals
For clarity, let's consider a table of metals whose density is closest to gold, as well as those used in alloys.
| Metal | Density (g/cm3) | Note |
| Iridium | 22.42 | Theoretically, these metals could increase the density of low-purity gold, but in practice, they are not used for counterfeits because they are significantly more expensive than gold itself. |
| Osmium | 22.5 | |
| Platinum | 21.45 | |
| Rhenium | 21.04 | |
| Gold (999 purity) | 19.32 | |
| Tungsten | 19.3 | The physical characteristics of tungsten differ significantly from gold. Even with a thick layer of gilding, it can be tested with a regular needle – it will easily penetrate a couple of millimeters and hit a hard metal, indicating a counterfeit. |
| Palladium | 12.0 | These metals are often used as alloying components for gold alloys. Silver provides malleability, palladium changes the color to white and increases the melting point, copper is responsible for hardness, and nickel also lightens the alloy but can cause allergic reactions. |
| Silver | 10.49 | |
| Copper | 8.94 | |
| Nickel | 8.907 |
The Influence of Gold Density on its Application
The high density of this precious metal determines many areas of its use.
- Investments: Thanks to its high density, even small investment coins and bars hold significant value. This allows large gold reserves to be stored in relatively small areas, which is beneficial for both private investors and national central banks. For example, a single small tube containing 20 "George the Victorious" gold coins with a nominal value of 50 rubles holds over 1.2 million rubles.
- Jewelry: Gold is valued not only for its beauty but also for its density, which, in alloys (750 and 585 purity), gives jewelry the necessary strength and wear resistance. Wedding rings and other constantly worn items can withstand contact with household chemicals, cosmetics, and sharp objects, maintaining their appearance and shape.
- Industry: In electronics, gold is indispensable due to its excellent conductivity and corrosion resistance. Gold-plated connectors and contacts in smartphones and computers ensure correct operation even with prolonged use. In the aerospace industry, thin gold films are used to protect satellites and spacecraft from thermal radiation and to prevent heat loss from within.
- Medicine: Gold is one of the most biocompatible metals, causing no allergic reactions or rejection by the body. It is used in the production of implants, pacemakers, staples, stents, braces, and crowns. Often, the main element is made from another strong metal and then coated with gold, creating a durable and safe structure.
It is noteworthy that the high density of gold formed the basis of the oldest method of its extraction — panning. Prospectors would wash gold-bearing sand, and the lighter minerals would be washed away by water, leaving behind the heavy gold.
Does the Density of Pure Gold Change?
The density of pure gold can change when heated. For example, when the metal transitions to a liquid state, which occurs at a melting point of approximately 1100 ⁰C, its density decreases from 19.32 g/cm³ to 17.17 g/cm³. However, upon subsequent cooling, gold fully restores its original density.
