When people suspect they have a valuable gold item, a common thought is to drop it into water to check for authenticity. This simple test is based on the knowledge that gold is an exceptionally heavy metal. The curiosity centers on whether materials used to imitate gold, often called “fake gold,” will behave the same way when submerged. Understanding the interaction between metals and water requires looking at the fundamental principles of physics.
The Direct Answer: Does Fake Gold Sink?
The immediate answer to whether fake gold sinks in water is yes. Most materials used to imitate gold are metallic alloys significantly heavier than water, causing them to sink instantly. Materials like brass and copper, frequently used as bases for gold plating, have densities that ensure they drop straight to the bottom.
If a piece of jewelry is made from common, inexpensive metals, the water test only confirms that the object is denser than water. This property is shared by nearly all metals. The quick result can be misleading because the simple act of sinking does not provide conclusive evidence of the object’s actual composition or if it is genuine gold.
The Science of Sinking: Density and Specific Gravity
The sinking or floating of any material is determined by its density, which is the amount of mass contained within a specific volume. Scientists often use the concept of specific gravity, which compares a material’s density to the density of water. Water has a specific gravity of 1.0; any substance with a specific gravity greater than 1.0 will sink, while anything less will float.
Pure gold has a specific gravity of approximately 19.3, making it 19.3 times heavier than an equal volume of water. Common fake gold materials like copper and brass have specific gravities between 8.5 and 8.9. Even these imitation materials are eight to nine times heavier than water, explaining why they sink just as quickly as real gold.
This substantial difference in specific gravity makes gold feel heavy compared to other metals of the same size. For instance, a small gold coin feels much heavier than a similarly sized silver coin, which has a specific gravity of about 10.5. Since 8.5 is still much larger than 1.0, the object will sink, regardless of whether it is authentic gold or a copper alloy.
Why the Water Test is Ineffective for Identification
The simple drop-in-water test fails as an identification method because it only confirms a density greater than 1.0, a characteristic of virtually all metallic counterfeits. It cannot distinguish between an object with a specific gravity of 8.5 (brass) and one with a specific gravity of 19.3 (gold). Furthermore, some high-end counterfeits use metals like tungsten, which has a specific gravity of nearly 19.25.
A gold-plated tungsten bar would sink and feel just as heavy as a solid gold bar, completely fooling the casual water test. Reliable identification requires a more precise measurement that leverages the extreme difference between the specific gravity of gold and other metals. This is done through the Archimedes principle, a non-destructive method that measures the exact volume of water displaced.
Using the Archimedes Principle
By accurately measuring the object’s mass in air and its apparent mass when submerged in water, one can calculate the object’s true specific gravity. This measurement allows for a comparison against the known value of 19.3. This reveals if the item is pure gold, a common alloy, or a cleverly disguised tungsten core. Other non-destructive options include using X-ray fluorescence (XRF) scanners or magnetic testing for ferromagnetic materials.