The gold standard 24k gold (pure gold) is soft so it is customarily alloyed with base metals for use in jewelry, thus giving rise to different looks and colors other than the bright yellow we normally associate with gold. Alloys with lower "k", typically 22k, 18k, 14k or 10k, contain higher percentages of copper, silver or other base metals in the alloy. Copper is the most commonly used base metal, yielding a redder metal. 18k gold containing 25% copper is found in antique and Russian jewelry and has a distinct, though not dominant, copper cast, creating rose gold. 14k gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges.

Blue gold is made by alloying gold with iron and purple gold can be made by alloying gold with aluminum, although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry, which is why you don't see it much. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold.

White gold alloys can be made with palladium or nickel. White 18 carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silver in appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe. Alternative white gold alloys are available based on palladium, silver and other white metals (World Gold Council), but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver.

Why is gold so valuable? It's scarce. Throughout all of history, only about 116,000 tons have been found...enough to make a cube about 59 feet on one side.

Gold is beautiful. Ancient cultures equated its brilliance with the sun. We still prize its glow in jewelry and ornaments.

Gold has properties valuable to industry. It is an excellent conductor of electricity and resists corrosion. Pure gold does not tarnish.

What to look for when buying gold jewelry Seems like these days gold jewelry is sold everywhere you see. And the price of gold recently hit an all-time high, so it's not just beautiful, it's an investment too. Here are a few tips to help you make a smart buying decision.

Jewelry crafted of real gold and sold as gold must be marked with its karatage. In addition, it must bear the manufacturer's trademark so that in case of fraud (using less gold than indicated by the karatage mark) the item can be traced back to the source. As you probably know, pure (24 karat) gold is too soft for most jewelry purposes, which is where the various karatages come into play. Gold is alloyed with other metals, such as silver or copper, to make it stronger and more durable. 14k gold is 585 parts gold out of 1000. This is why you sometimes see a 585 mark on 14k jewelry. 18k gold is 750 parts gold out of 1000. So if you had two identical chains, one 14k and one 18k, the 18k chain would be more expensive since more gold was used in its manufacture.

Weight will affect value and durability. When buying a rope or cable chain, check to make sure the wire strands are not hollow or they may break easily and ruin the look of the chain. A slender lightweight gold bracelet may get snagged and snap in half. Clearly a heavier piece of jewelry will cost more when it is gold...sometimes quite a bit more.

Check country of origin. Italy is famous for top-quality gold and silver jewelry. You really can't go wrong buying Italian gold. A lot of cheaper gold jewelry today comes from China. These pieces may have a greenish cast to them and may not have as much gold as claimed by the karatage mark.