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Gold and Karatage
When you buy gold jewelry, it isn't pure gold. Pure gold is seldom used for jewelry because it is too soft. Gold is combined with other metals to make it more durable for jewelry use. The gold in your jewelry is actually an alloy, or mixture of metals. The purity, or fineness is indicated by its karat number.
Pure gold is stated as 24 karat. Each karat represents 1/24 of pure gold. The gold content of an 18K jewelry item is therefore 18/24 or 75% pure gold. According to the European system, 18K gold is marked 750, 14K gold is marked 585, 10K gold is marked 420.
10K gold is the lowest percentage allowed to be marked and sold as Karat Gold Jewelry in the United States. Underkarating (stamping a karatage as higher than the item actually contains) does occur, but most of it goes undetected because it is not possible to analyze gold jewelry for its karatage without damaging the jewelry in the process.
So, what metals are alloyed with gold? To keep gold it’s beautiful golden color, silver, copper, and zinc are the most common alloys used. However, other metals or different percentages may be used to make colored gold.
The presence of other metals in gold produces the various colors of gold.
Below are a few samples of the alloy percentages used to make colored gold. These alloys and percentages may vary depending on the supplier.
18K Red - 75% gold & 25% copper
18K Rose - 75% gold, 22.25% Copper & 2.75% Silver
18K Pink - 75% gold, 20% copper & 5% silver
18K White - 75% gold, 10% palladium, 10% nickel & 5% Zink
18K Green - 75% gold, 20% silver & 5% copper
18K Blue - 75% gold & 25% iron
19K Purple - 80% gold & 20% aluminum
Platinum is one of the softest metals. But when it is alloyed with other metals, normally 10% iridium, it becomes one of the hardest metals. This hardness makes platinum ideal for jewelry with diamonds and other valuable stones because it provides the most secure material for setting gems.
Platinum is white in color and is often mistaken for white gold. However, platinum carries higher costs than gold because it is denser and is more difficult to fabricate, due to its higher melting point.
U.S. law governing trademarks and quality marks for gold and silver do not yet apply to platinum, but this is being changed. Europe and Canada already include platinum in their marking laws.
Silver is the whitest of the precious metals and the most lustrous. It reflects 95 percent of the light that hits it, compared with 92 percent for gold.
Next to gold, silver is the most malleable metal — it can be formed into sheets (or leaves) .00025 millimeter thick. It is second only to gold as a ductile metal. A gram of silver can be drawn out into a wire a mile long.
Silver in its pure form is almost never used in jewelry because it is too soft. It also has a tendency to tarnish.
The addition of a very small amount of copper increases the durability of silver. British silversmiths discovered that an alloy of 925 parts silver and 75 parts copper was ideal, hence the term "sterling standard." Items stamped "sterling" meet this purity standard, as set forth in the National Gold and Silver Marking Act. Sterling silver is also called silver, sterling, or solid silver.