horn") (diminutive of – , "horn"). In 309 CE, Roman Emperor Constantine I began to mint a new gold coin solidus that was of a libra (Roman pound) of gold equal to a mass of 24 siliquae, where each siliqua (or carat) was of a libra. This is believed to be the origin of the value of the karat. Verifying fineness While there are many methods of detecting fake precious metals, there are realistically only two options available for verifying the marked fineness of metal as being reasonably accurate: assaying the metal (which requires destroying it), or using X-ray fluorescence (XRF). XRF will measure only the outermost portion of the piece of metal and so may get misled by thick plating. That becomes a concern because it would be possible for an unscrupulous refiner to produce precious metals bars that are slightly less pure than marked on the bar. A refiner doing $1 billion of business each year that marked .980 pure bars as .999 fine would make about an extra $20 million in profit. In the United States, the actual purity of gold articles must be no more than .003 less than the marked purity (e.g. .996 fine for gold marked .999 fine), and the actual purity of silver articles must be no more than .004 less than the marked purity. Fine weight A piece of alloy metal containing a precious metal may also have the weight of its precious component referred to as its "fine weight". For example, 1 troy ounce of 18 karat gold (which is 75% gold) may be said to have a fine weight of 0.75 troy ounces. Most modern government-issued bullion coins specify their fine weight. For example, the American Gold Eagle is embossed One Oz. Fine Gold and weighs 1.091 Troy oz. Troy mass of silver content Fineness of silver in Britain was traditionally expressed as the mass of silver expressed in troy ounces and pennyweights ( troy ounce) in one troy pound (12 troy ounces) of the resulting alloy. Britannia silver has a fineness of 11 ounces, 10 pennyweights, or about silver, whereas sterling silver has a fineness of 11 ounces, 2 pennyweights, or exactly silver. See also Colored gold Electrum Gold as an investment Gold coin Platinum coin Silver as an investment Silver coin Tumbaga References External links Metallurgy Gold investments Precious metals Units of purity Jewellery making es:Ley (pureza)