Introduction Gold and silver have been used as a store of value and a widely accepted currency for thousands of years. For as long as gold and silver have had value, then unscrupulous people have been making fakes. And for as long as fakes have been made, then tests to identify those fakes have been devised; ranging from a simple bite into gold coins, to the discovery of the principal of specific gravity, to the latest high tech laboratory analysis.
Specific Gravity Specific gravity testing came about some 250 years before the birth of Christ, when Greek King Heiro II commissioned Archimedes to find out if a goldsmith had cheated him in the crafting of a new crown. The problem was solved when Archimedes noticed that the amount of water displaced by an object when it is immersed in water is equal to its volume. He realized that objects of the same mass would displace differing amounts of water depending on their density, or specific gravity (SG). Archimedes is claimed to have yelled “Eureka” upon the discovery, and the king’s suspicions about the goldsmith were then proven to be well-founded.
Specific Gravity Upon the discovery of specific gravity, faking gold objects with exact dimensions became more difficult as few substances are as dense as gold, which has an SG of 19.3. This means gold weighs 19.3 times as much as the same volume of water. Platinum is slightly denser than gold. During some periods of history platinum has been alloyed with lighter metals to fake gold when the price of platinum was a lot less than gold. Right now platinum is a little more expensive than gold, making that opportunity uneconomic.
Faking Gold with Tungsten However, there is another metal which is very nearly the same density as gold and relatively cheap. That metal is tungsten. Up until recent times it was difficult to create convincing fakes of gold with tungsten because tungsten is very brittle, so it is difficult to emboss or stamp, unlike gold which is very soft. Unfortunately the Chinese have recently used modern machining techniques to make gold-coated tungsten fakes of many different bullion and coin products. These fakes can be found all over Chinese trade sites on the internet, and they appear in the news when westerners discover they have been defrauded. Some of the fakes are so perfect the manufacturers can command asking prices that are nearly half the equivalent gold value of the real item, even though the fakes only contain a few dollars worth of gold.
Faking silver with base metals In the case of silver, the manufacturers of counterfeits have a greater choice of metals to use for faking silver bars and coins and still achieve the correct weight and dimensions. Base metal alloys with any range of combinations of copper, tin, lead, zinc and iron can be used as an inner core to counterfeit silver bullion and coins with a pure silver shell, coating or plating at the surface.
Coating and plating fakes The coating or plating of gold and silver used in the manufacture of fakes with perfect weight, dimension and appearance is usually thick enough to fool X-ray Fluorescence (XRF) testing, which is only capable of penetrating a few tens of microns beneath the surface. Nowadays it is becoming increasingly common for dealers to refuse to buy gold and silver bullion, bars and coins from the public without undertaking some sort of destructive test. This may entail attempting to scratch off any surface plating, or even cutting into the metal itself.
Another property – sound velocity However, there remains another physical property that can differentiate between real gold and silver bullion products and counterfeits, without having to destroy them. That property is the velocity that sound waves travel through metal. Metals have a range of sound velocities depending on both their density and hardness. Even though tungsten and gold have very similar densities, the great difference in their hardness results in a sound velocity of 3240 m/s for pure gold and 5400 m/s for tungsten. The sound velocity for silver is 3620 m/s and the alloys used to fake silver typically register sound velocities higher than 4000 m/s.
Use ultrasound to test silver and gold bars and bullion The way to test silver bars and gold bullion for sound velocity is by using ultrasound. Ultrasound testing of silver and gold for sound velocity is affordable and can be done conveniently in your own home. To find about the technology and how it can save investors and dealers from being defrauded by counterfeit gold and silver, visit http://testyourgold.com/.