Gold, Silver, Jewellery

Because of the softness of pure (24k) gold, it is usually mixed with base metals for use in jewelry, altering hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k,, 18k 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. 

Unique Gold Jewellery

Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and referred to as green gold. White gold alloys can be with palladium or nickel. White 18 carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper silvery appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe.

Fourteen carat gold-copper alloy is nearly identical in color certain bronze alloys, and both may be used to produce police and other badges. Eighteen carat gold containing 25% copper found in antique and Russian jewelry and has a, distinct though not dominant, copper cast, creating rose gold. Blue Gold is made with an alloy of iron and purple gold can be made by alloying with aluminum, although rarely done except in specialized jewelry. Blue gold is more fragile and therefore more difficult to work with when making jewelry.

Alternative white gold alloys are available based on palladium, silver and other white metals, but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than either pure silver or sterling silver. Copper is the metal most commonly used base, resulting in a red color. Japanese Craft Mokume-Gane utilizing contrasting colors between laminated colored gold alloys to produce mapalamuting wood-grain effect.

Source: Wikipedia