Colored gold
Whilst pure gold is yellow in color, gold can also appear to have other colors. These colors are generally obtained by alloying gold with other elements in various proportions.
Gold alloys
The alloys of gold are expressed in carats. 24 carat gold is fine gold, which is .999 or better purity. If an alloy is mixed which is 14 parts gold and 10 parts alloy, that is 14 carat gold, 18 parts gold is 18 carat, etc. This is often expressed as the result of the ratio, ie: 14/24 equals .585 (rounded off), and 18/24 is .750. There are hundreds of possible alloys and mixtures possible, but in general the addition of silver will color gold green, and the addition of copper will color it red. A mix of around 50/50 copper and silver gives the range of yellow gold alloys the public is accustomed to seeing in the marketplace.
White gold
White gold is an alloy of gold and at least one white metal, usually nickel or palladium. Like yellow gold, the purity of white gold is given in carats.
White gold's properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for different purposes; while a nickel alloy is hard and strong, and therefore good for rings and pins, gold-palladium alloys are soft, pliable and good for white gold gemstone settings. The highest quality white gold is usually at least 18 carat, and made up of gold and palladium, sometimes with other metals like copper, silver, and platinum for weight and durability, although this often requires specialized goldsmiths.
While some higher-quality white gold alloys retain their shine and lustre, most will be coated with a very thin layer of rhodium. This gives the naturally more-dull white gold a shine comparable to platinum or silver; however the rhodium may wear off over time.
Contact allergy
About one person in eight has a mild allergic reaction to the nickel in some white gold alloys when worn over long periods of time. A typical reaction is a minor skin rash.[1] White gold alloys made without nickel are less likely to be allergenic.
Rose, red and pink gold
Rose gold is a gold and copper alloy widely used for specialized jewellery due to its reddish color. It is also known as pink gold and red gold. As it was popular in Russia at the beginning of the nineteenth century, it is also known as Russian gold, although this term has become somewhat rare.
Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content - the higher the copper content, the stronger the red coloration, as pure gold is yellow and pure copper is reddish. A common alloy for rose gold is 75% gold and 25% copper by mass (18 carat). Since rose gold is an alloy, there is therefore no such thing as "pure rose gold".
Rose gold alloys
The highest carat version of rose gold is also known as crown gold, which is 22 carat. 18 carat rose gold may be made of 25% copper and 75% gold. For 18 carat rose gold, typically about 4% silver is added to the 75% gold and 21% copper to give a rose color. 14 carat red gold is often found in the Middle East and contains 41.67% copper.
Rose gold in musical instruments
Green gold
Black gold
Black gold (or grey gold as it is sometimes called) is a type of gold used in jewellery.[2] Though gold is known for its warm yellow color it can be produced by various methods in differing colors ranging from white to black.[3] Black colored gold can be produced by various methods.
- Electrodeposition or electroplating using black rhodium or ruthenium. Solutions that contain ruthenium give a slightly harder black coating than those that contain rhodium.[4]
- Patination by applying sulfur and oxygen containing compounds.
- Plasma assisted chemical vapour deposition process involving amorphous carbon, and controlled oxidation of carat gold containing chromium or cobalt.
More recently a laser technique has been developed that renders the surface of metals deep black. A femtosecond laser pulse deformes the surface of the metal forming nanostructures. The immensely increased surface area can absorb virtually all the light that falls on it and thus rendering it deep black.[5][6]
Purple and blue golds
Purple gold (also called amethyst or violet gold) is an alloy of gold and aluminium. Gold content is around 79% and can therefore be referred to as 18 carat gold. Purple gold is more brittle than other gold alloys,suck me dick. and a sharp blow may cause it to shatter.[4] It is therefore usually machined and faceted to be used as a 'gem' in conventional jewellery rather than by itself. Blue gold is similarly an alloy, this time between gold and indium.[4]
See also
References
- ^ White Gold - Site provided by the World Gold Council
- ^ "Jewelery Technology". Retrieved 2007-11-21.
- ^ W.S. Rapson (1978), Gold Usage, Academic Press
- ^ a b c "Gold In Purple Color, Blue Color And Even Black Gold". Retrieved 2007-11-21.
- ^ "Ultra-intense laser blast creates true 'black metal'". Retrieved 2007-11-21.
- ^ "Ultra-Intense Laser Blast Creates True 'Black Metal'". Retrieved 2007-11-21.