Pure gold is slightly reddish yellow, but golden in various other colors can be produced.
Colored gold can be classified into three groups:
- Alloy with silver and copper in various proportions, producing white, yellow, green and red gold. These are usually soft alloys.
- Intermetallic compounds, producing blue and purple gold, and other colors. These are usually fragile, but can be used as gems and inlays.
- Surface treatment, such as the oxide layer.
Pure 100% (in practice, 99.9% or better) gold is 24 carat by definition, so all the colored gold is less than this, with common ones being 18K (75%), 14K (58.5%), 10K ( 41.6%), and 9K (37.5%).
Video Colored gold
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White Gold is a gold alloy and at least one white metal (usually nickel, manganese, or palladium). Like yellow gold, the purity of white gold is given in the karats.
The white gold properties vary depending on the metal used and the proportions. As a result, white gold alloys can be used for various purposes; while hard and strong nickel alloys, and therefore, both for rings and pins, soft-palladium gold alloys, supple, and fine for white gold gemstones, sometimes with other metals, such as copper, silver, and platinum, are added for weight and endurance (though this often requires a special goldsmith). The term white gold is used very loosely in the industry to describe a gold alloy of rust with whitish color. It is a common misconception that rhodium coating colors, which are seen on many commercial pieces, are actually white gold colors. The term "white" includes a large spectrum of bordered or overlapping colors of pale yellow, brown, and even a very pale rose. The jewelry industry often hides this white color with rhodium plating.
The general white gold formulation comprises 90% by weight of gold and 10% by weight of nickel. Copper can be added to increase flexibility.
The gold-nickel-copper alloy strength is due to the formation of two phases, the rich gold Au-Cu, and nickel-rich Ni-Cu, and the hardening of the resulting material.
The alloys used in the jewelry industry are gold-palladium-silver and gold-nickel-copper-zinc. Palladium and nickel act as a primary bleaching agent for gold; zinc acts as a secondary whitening agent to dilute copper color.
Nickel used in some white gold alloys can cause allergic reactions when used for a long time (also especially on several hours of watches). This reaction, usually a mild skin rash from nickel dermatitis, occurs in about one in eight people; Because of this, many countries do not use nickel in their white gold formulations.
Yellow gold
Common alloy examples for 18K yellow gold:
- 18K Yellow gold: 75% gold, 12.5% ​​copper, 12.5% ​​silver
- 18K Yellow (darker) gold: 75% gold, 15% copper, 10% silver
Rose, red, and pink gold
Rose gold is a gold-copper alloy that is widely used for special jewelry. Rose gold, also known as pink gold and red gold, was popular in Russia in the early nineteenth century, and is also known as Russian gold b> , even though the term is now obsolete. Rose gold jewelry is becoming more popular in the 21st century, and is generally 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 content of copper: the higher the copper content, the stronger the red. Pink gold uses the smallest copper, followed by rose gold, with red gold having the highest copper content. Common alloy examples for 18K gold, 18K red gold, 18K pink gold, and 12K red gold:
- 18K red gold: 75% gold, 25% copper
- 18K gold rose: 75% gold, copper 22.25%, silver 2.75%
- 18K pink gold: 75% gold, 20% copper, 5% silver
- 12K red gold: 50% gold and 50% copper.
Up to 15% zinc can be added to rich copper alloys to change their color to reddish yellow or dark yellow. Red gold 14K, often found in the Middle East, contains 41.67% copper.
The highest carat version of rose gold, also known as gold crown, is 22 carats.
During ancient times, because of the feces in the process of smelting, gold often turns reddish. This is why many Greco-Roman texts, and even many texts from the Middle Ages, describe gold as "red".
Spangold
Some gold copper-aluminum alloys form a fine surface texture in heat treatment, producing an interesting spangling effect. In cooling, they undergo a quasi-martensitic transformation of the center-centered cubic phase to the body-centered tetragonal phase; the transformation does not depend on the cooling rate. Polished objects heated in hot oil up to 150-200 Â ° C for 10 minutes then cooled below 20 Â ° C, forming a glistening surface that is covered with a small side.
76% gold alloys, 19% copper, and 5% aluminum produce yellow; 76% gold alloy, 18% copper and 6% pink aluminum.
Green gold
Green gold is known by Lydia since 860 BC under the name of electrum, silver and gold alloys that occur naturally. It really looks like greenish yellow rather than green. Enamel fired attaches better to this alloy than pure gold.
Cadmium can also be added to the gold alloy to create a green color, but there are health problems regarding its use, because cadmium is very toxic. Alloys of 75% gold, 15% silver, 6% copper, and 4% cadmium produce dark green alloys.
Gray gold
Gray gold alloys are usually made of gold and palladium. A cheaper alternative that does not use palladium is made by adding silver, manganese, and copper to gold in certain ratios.
Maps Colored gold
Intermetallic
All intermetallic AuX 2 has a fluorite crystal structure (CaF 2 ), and is therefore fragile. The deviation of stoichiometry results in a loss of color. Few nonstoichiometric compositions are used, however, to achieve a microstructure of two or three smooth phases with reduced brittleness. Another way to reduce the fragility is to add a small amount of palladium, copper, or silver.
Intermetallic compounds tend to have poor corrosion resistance. The less noble elements are washed into the environment, and gold-rich surface layers are formed. Direct contact of blue and purple gold elements with the skin should be avoided because exposure to sweat can lead to metal washing and metal surface color change.
purple gold
Purple gold (also called amethyst gold and violet gold) is a gold and aluminum alloy that is rich in gold-aluminum intermetallic (AuAl 2 ). The gold content in AuAl 2 is about 79% and hence can be termed as 18 karat gold. Purple gold is more brittle than other gold alloys (a serious mistake when formed in electronics), because it is an intermetallic compound rather than a soft alloy, and a sharp blow can cause it to crumble. Therefore it is usually machine and facet to be used as a "gem" in conventional jewelry than by itself. In lower gold content, this material comprises intermetallic solid and aluminum-rich solid phase. In higher gold content, a richer metallic metallic AuAl form; purple color is maintained up to about 15% of aluminum. At 88% gold, the material is made up of AuAl and discolored. The AuAl 2 composition is actually closer to Al 11 Au 6 because the sub-grid is not fully occupied.
Blue gold
Blue gold is a gold and gallium or indium alloy. The indium-gold contains 46% gold (about 11 carats) and 54% indium, forming the interinall AuIn 2 . While some sources say this intermetallic has a "clear blue", in fact the effect is slight: AuIn 2 has CIE LAB 79, -3.7, -4.2 color coordinates that look rough as the color gray. With gallium, gold forms AuGa intermetallic 2 (58.5% Au, 14ct) which has a bluish blue color. The AuIn point 2 is 541Ã, Â ° C, for AuGa 2 is 492Ã, Â ° C. AuIn 2 less fragile than AuGa 2 , which in itself is less fragile than AuAl 2 .
The surface of the blue gold plating on stainless gold or sterling silver can be achieved by coating the gold from the surface, followed by indium coating, with a coating thickness corresponding to the atomic ratio of 1: 2. The heat treatment then causes metal interdiffusion and the formation of the necessary intermetallic compound.
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Black gold is a type of gold used in jewelry. Black gold can be produced by various methods:
- Electroplating, using black rhodium or ruthenium. Solutions containing ruthenium provide a slightly tougher black coating than those containing rhodium.
- Patina using a compound containing sulfur and oxygen.
- Plasma-assisted chemical vapor deposition process involving amorphous carbon
- Controlled oxidation of gold containing chromium or cobalt (eg 75% gold, 25% cobalt).
The various colors from brown to black can be achieved on copper alloys rich in treatment with potassium sulfide.
Alloys containing cobalt, eg. 75% gold with 25% cobalt, forming a black oxide coating with heat treatment at 700-950 ° C. Copper, iron and titanium can also be used for the effect. Chromium-cobalt alloys (75% gold, 15% cobalt, 10% chromium) produce an olive-colored surface oxide because of the chromium (III) oxide content, about five times thinner than Au-Co and significantly better. wear resistance. The gold-cobalt alloy consists of a gold-rich phase (about 94% Au) and rich in cobalt (about 90% Co); rich cobalt phase grains are capable of forming an oxide layer on its surface.
More recently, black gold can be formed by creating nanostructures on the surface. The femtosecond laser pulse damages the metal surface, creating a highly elevated surface area that absorbs almost any light that falls onto it, thus making it black, but this method is used in high-tech applications rather than for appearance in jewelry. The darkness is caused by the excitation of local surface plasmons that create strong absorption in various plasmon resonances. The extent of plasmon resonance, and the wavelength of absorption, depends on the interaction between different gold nanoparticles.
Blue gold
The oxide layer can also be used to obtain blue gold from and alloys of 75% gold, 24.4% iron, and 0.6% nickel; the coating is formed on the heat treatment in the air between 450-600 Â ° C.
A rich sapphire-blue gold of 20-23K can also be obtained by alloying with ruthenium, rhodium and three other elements and heat treatment at 1800 ° C, to form a thick, 3-6 micrometer thick colored surface oxide layer.
See also
References
External links
Source of the article : Wikipedia
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