Colored gold is the name given to any gold that has been treated using techniques to change its natural color. Pure gold is slightly reddish yellow in color,[1] but colored gold can come in a variety of different colors by alloying it with different elements.
Colored golds can be classified in three groups:[2]
Pure 100% (in practice, 99.9% or better) gold is 24 karat by definition, so all colored golds are less pure than this, commonly 18K (75%), 14K (58.5%), 10K (41.6%), or 9K (37.5%).[3]
Alloys
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White gold
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Rhodium-plated white gold wedding ringThe word white covers a broad range of colors that borders or overlaps pale yellow, tinted brown, and even very pale rose. White gold is an alloy of gold and at least one white metal (usually nickel, silver, platinum or palladium).[4] Like yellow gold, the purity of white gold is given in karats.
White gold's properties vary depending on the metals used and their proportions. A common white gold formulation consists of 90% wt. gold and 10% wt. nickel.[3] Copper can be added to increase malleability.[2] The alloys used in the jewelry industry are gold-palladium-silver and gold-nickel-copper-zinc. Palladium and nickel act as primary bleaching agents for gold; zinc acts as a secondary bleaching agent to attenuate the color of copper.[citation needed] As a result, white gold alloys can be used for many different purposes. Nickel alloys are hard and strong, and therefore good for rings and pins. Gold-palladium alloys are soft, pliable, and good for white-gold gemstone settings. The strength of gold-nickel-copper alloys is caused by formation of two phases: a gold-rich Au-Cu, and a nickel-rich Ni-Cu, and the resulting hardening of the material.[2]
The nickel used in some white gold alloys can cause an allergic reaction when worn over long periods (also notably on some wristwatch casings).[5] This reaction, typically a minor skin rash from nickel dermatitis, occurs in about one out of eight people; because of this, many countries do not use nickel in their white gold formulations.
Yellow gold
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Gold is rarely pure gold, even before another metal is added to make a white gold alloy, and can contain mercury from its production that can cause an allergic reaction.[6]
Examples of the common alloys for 18K yellow gold include:[citation needed]
Rose, red, and pink gold
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"Rose Gold" redirects here. For the album by Shekhinah, see Rose Gold (album)
"Rosegold" redirects here. For the album by Ashley Monroe, see Rosegold (album)
Rose gold diamond engagement ringRose gold is a gold-copper alloy[7] widely used for specialized jewelry. Rose gold, also known as pink gold and red gold, was popular in Russia at the beginning of the 19th century, and was also known as Russian gold.[citation needed] Rose gold jewelry is becoming more popular in the 21st century, and is commonly used for wedding rings, bracelets, and other jewelry.
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. Pink gold uses the least copper, followed by rose gold, with red gold having the highest copper content. Examples of the common alloys for 18K rose gold, 18K red gold, 18K pink gold, and 12K red gold include:[3]
Up to 15% zinc can be added to copper-rich alloys to change their color to reddish yellow or dark yellow.[2] 14K red gold, often found in the Middle East, contains 41.67% copper.
The highest karat version of rose gold, also known as crown gold, is 22 karat. Amongst the alloys made of gold, silver, and copper, the hardest is the 18.1 K pink gold (75.7% gold and 24.3% copper). An alloy with only gold and silver is the hardest at 15.5 K (64.5% gold and 35.5% silver).
During ancient times, due to impurities in the smelting process, gold frequently turned a reddish color. This is why many Greek and Roman texts, and some texts from the Middle Ages, describe gold as "red".[citation needed]
Spangold
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Some gold-copper-aluminium alloys form a fine surface texture at heat treatment, yielding an interesting spangling effect. At cooling, they undergo a quasi-martensitic transformation from body-centered cubic to body-centered tetragonal phase; the transformation does not depend on the cooling rate. A polished object is heated in hot oil to 150–200 °C for 10 minutes then cooled below 20 °C, forming a sparkly surface covered with tiny facets.
The alloy of 76% gold, 19% copper, and 5% aluminium yields a yellow color; the alloy of 76% gold, 18% copper, and 6% aluminium is pink.[2]
Green gold
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Green gold was known to the ancient Persians as long ago as 860 BC under the name electrum, a naturally occurring alloy of silver and gold.[3] However, electrum was used even thousands of years before that, by both the Akkadians and Ancient Egyptians (as evidenced by the Royal Cemetery at Ur). Even the tops of some Egyptian pyramids were known to be capped in thin layers of electrum. It actually appears as greenish-yellow rather than green. Fired enamels adhere better to these alloys than to pure gold.
Cadmium can also be added to gold alloys to create a green color, but there are health concerns regarding its use, as cadmium is highly toxic.[8] The alloy of 75% gold, 15% silver, 6% copper, and 4% cadmium yields a dark-green alloy.
Grey gold
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Grey gold alloys are usually made from gold and palladium. A cheaper alternative which does not use palladium is made by adding silver, manganese, and copper to the gold in specific ratios.[9]
Intermetallic
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All the AuX2 intermetallics have the fluorite (CaF2) crystal structure, and, therefore, are brittle.[2] Deviation from the stoichiometry results in loss of color. Slightly nonstoichiometric compositions are used, however, to achieve a fine-grained two- or three-phase microstructure with reduced brittleness. Another way of reducing brittleness is to add a small amount of palladium, copper, or silver.[10]
The intermetallic compounds tend to have poor corrosion resistance. The less noble elements are leached to the environment, and a gold-rich surface layer is formed. Direct contact of blue and purple gold elements with skin should be avoided as exposure to sweat may result in metal leaching and discoloration of the metal surface.[10]
Purple gold
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Purple gold (also called amethyst gold and violet gold) is an alloy of gold and aluminium rich in gold–aluminium intermetallic (AuAl2). Gold content in AuAl2 is around 79% and can therefore be referred to as 18 karat gold. Purple gold is more brittle than other gold alloys (called the "purple plague" when it forms and causes serious faults in electronics[11]), as it is an intermetallic compound instead of a malleable alloy, and a sharp blow may cause it to shatter.[12] It is therefore usually machined and faceted to be used as a "gem" in conventional jewelry rather than by itself. At a lower content of gold, the material is composed of the intermetallic and an aluminium-rich solid solution phase. At a higher content of gold, the gold-richer intermetallic AuAl forms; the purple color is preserved to about 15% of aluminium. At 88% of gold the material is composed of AuAl and changes color. The actual composition of AuAl2 is closer to Au6Al11 as the sublattice is incompletely occupied.[2]
Blue gold
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Blue gold is an alloy of gold and either gallium or indium.[12] Gold-indium contains 46% gold (about 11 karat) and 54% indium,[3] forming an intermetallic compound AuIn2. While several sources remark this intermetallic to have "a clear blue color",[2] in fact the effect is slight: AuIn2 has CIE LAB color coordinates of 79, −3.7, −4.2[10] which appears roughly as a greyish color. With gallium, gold forms an intermetallic AuGa2 (58.5% Au, 14ct) which has slighter bluish hue. The melting point of AuIn2 is 541 °C, for AuGa2 it is 492 °C. AuIn2 is less brittle than AuGa2, which itself is less brittle than AuAl2.[10]
A surface plating of blue gold on karat gold or sterling silver can be achieved by a gold plating of the surface, followed by indium plating, with layer thickness matching the 1:2 atomic ratio. A heat treatment then causes interdiffusion of the metals and formation of the required intermetallic compound.
Surface treatments
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Black gold
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black gold, seeFor the colloquial term, see crude oil
Black gold is a type of gold used in jewelry.[13][14] Black-colored gold can be produced by various methods:
A range of colors from brown to black can be achieved on copper-rich alloys by treatment with potassium sulfide.[2]
Cobalt-containing alloys, e.g. 75% gold with 25% cobalt, form a black oxide layer with heat treatment at 700–950 °C. Copper, iron and titanium can be also used for such effect. Gold-cobalt-chromium alloy (75% gold, 15% cobalt, 10% chromium) yields a surface oxide that is olive-tinted because of the chromium(III) oxide content, is about five times thinner than Au-Co and has significantly better wear resistance. The gold-cobalt alloy consists of gold-rich (about 94% Au) and cobalt-rich (about 90% Co) phases; the cobalt-rich phase grains are capable of oxide-layer formation on their surface.[2]
More recently, black gold can be formed by creating nanostructures on the surface. A femtosecond laser pulse deforms the surface of the metal, creating an immensely increased surface area which absorbs virtually all the light that falls on it, thus rendering it deep black,[15] but this method is used in high technology applications rather than for appearance in jewelry. The blackness is due to the excitation of localized surface plasmons which creates strong absorption in a broad range in plasmon resonance. The broadness of the plasmon resonance, and absorption wavelength range, depends on the interaction between different gold nanoparticles.[16]
Blue gold
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Oxide layers can also be used to obtain blue gold from an alloy of 75% gold, 24.4% iron, and 0.6% nickel; the layer forms on heat treatment in air between 450 and 600 °C.[2]
A rich sapphire blue colored gold of 20–23K can also be obtained by alloying with ruthenium, rhodium, and three other elements and heat-treating at 1800 °C, to form the 3–6 micrometers thick colored surface oxide layer.[2]
See also
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References
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Gold has been around since the dawn of time, and it never ceased to mesmerize different civilizations with its brilliance, durability, and elegant appearance. Even now gold still remains a symbol of wealth thanks to its different styles and colors such as; white, yellow, black, purple, and rose gold. Each gold color presents a different feeling and style however the most popular ones have always been yellow, white, and rose gold.
An important fact about gold to keep in mind is that real gold does not change color. If you observe discolored gold, then your jewelry is not real gold.
With its ever-increasing popularity, a more affordable and faux version of gold-colored jewelry has also become a global trend. As hard as it seems, you can tell the difference between real gold and fake gold jewelry through a few simple steps you can do at home. Here we have compiled a list of useful steps to test the genuinely of any gold jewelry.
How to Test if Gold is
Real
at Home?
If you have come across a piece of jewelry that you're unsure not sure of, like a vintage gold piece of jewelry, here are some of the easy tests you can do at home to find out:
rop your gold jewelry into a jug filled with water. Gold is quite a dense metal that will directly sink into the water. If your jewelry floats, it is not made of real gold.
Apply droplets of vinegar or soak your jewelry in water. If it changes color, it is not real gold.
Observe any tarnishes or damages that might be caused due to time. Real gold should not expose to any different
color if it gets damaged or tarnished. You can check the edges of your jewelry to see any wear marks and if any other color is exposed. Gold-plated jewelry often rubs off in time.
Colored wear marks also indicate that your jewelry is not 100% genuine.Gold does not react to magnets. You can test your jewelry with a strong magnet. If it is pulled by its force, it is a strong indication that it is not real.
Check for the number on your jewelry. Gold jewelry should have numbers engraved on o
r inside them. These numbers give information about its karat value
. These can generally be found on the inner side of the rings or bracelets while on necklaces, they can be found on the clasps.
A more certain method to test your jewelry is by purchasing gold testing kit online. Alternatively, you can bring your jewelry to your local jeweler to weigh your jewelry.
All in all, gold does not really change its color. But since it is quite a soft metal, it is mixed with other metals to create an alloy. Therefore, gold can show its base elements’ color if it is deeply damaged. However, under normal conditions when it is maintained properly, the surface of the gold can only get oxidized. This layer can be cleaned by jewelry stores.
How to tell if gold is real?
Real gold jewelry pieces are always stamped with a 'hallmark', either on the clasp or on one of the ends of the piece. This hallmark should contain numbers or letters to indicate the composition of the jewelry piece and its karat value.
How to know if gold is real?
If there isn't a hallmark on your gold, check for any discoloration on your jewelry. Real gold does not change color, so if your gold exposes different colors or leaves green marks on your skin, it is not real gold. Alternatively, you can test your gold with a magnet or by dropping it in water.
How to check if gold is real with a lighter?
Gold is an incredibly durable and resistant metal. To test your if your gold is real, you can try holding a lighter to it. If the piece turns black, it is not real gold.
How to tell if a gold chain is real?
Before purchasing a gold chain, always make sure to check the clasp for a hallmark. Real gold chains will always have their karat value stamped on the back of the lock. If there isn't a hallmark, there is a high chance that the chain is not real gold. If you're buying vintage jewelry, we would advise bringing your chain to your local jeweler.
How to tell if a necklace is real gold?
Real gold necklaces will almost always have a hallmark stamped on the clasp of the necklace. If your necklace is missing a hallmark, you can try the lighter technique. If you hold a lighter to your necklace and it changes color, it is not real gold.
How to tell if a ring is real gold?
If you're not sure about whether your necklace is made of real gold, one at-home way to check is to drop it into a jug full of water. Gold is a dense metal so your necklace should fall directly to the bottom of the jug. Additionally, you can hold a magnet to your necklace. If there is a magnetic pull, your necklace is probably not real gold.
Does 14K gold tarnish
and lose its color
?
Gold can lose its shine and vibrant yellow color in time due to daily wear and the chemicals and water it is exposed to. However, gold is a highly durable metal that is resistant to tarnishing and corrosion. If your 14K gold is alloyed with high quality metals, it should not tarnish.
Does 18K gold tarnish?
Real gold is highly tarnish-proof. Since gold is a soft and malleable metal, it is mixed with other metals to create an alloy. The lower the karat value, the more other metals there are in the alloy. 18K means that 75% of the alloy is pure gold. With such a high percentage, your 18K gold can protect its form and brilliance if it is looked after properly. Otherwise, it can get tarnished over the years.
Does gold oxidize?
Pure gold is a highly resistant metal that does not oxidize. However, gold can get darker in time due to its alloy metals' exposure to oxygen and wet seasons as in summer; gold earrings changing color might be a common issue for many during this season. However, you can protect its shine and take care of your gold jewelry by purchasing a solution removing oxidized layer that builds up in time.
Under normal conditions, gold should not change color. However, due to use and time, it may get scratched and tarnished which can damage the cosmetic look of the gold.
Does gold plated jewelry
change color?
Plated gold should rub off after a while and lose its color.
Can you change white gold to yellow gold?
White gold cannot be changed to yellow gold.
Can you change yellow gold to white gold?
White gold is actually an alloy of yellow gold with another white metal, generally rhodium. Although you cannot change the the chemical structure, you can always get your yellow gold jewelry dipped in rhodium to get a white gold effect.
Does 14K gold chan
ge color?
No matter the karat value, gold does not change color.
Does 10K gold change color?
Pure gold is a very soft metal. To make it durable enough for daily wear, it must be mixed with other metals to create a stronger alloy. Although pure gold does not change color, if your jewelry gets tarnished, the other metals in the alloy may show signs of color.
Does real gold turn green?
Real gold does not turn green. If it also leaves a green mark on your finger, it is likely that its base material is copper.
Does 18K gold tarnish
and can you shower with gold on?
Gold is a metal that's resistant to corrosion. Water does not damage gold however it may cause it to lose its shine over time. You can definitely shower with your gold jewelry, but it may need to be polished once in a while.