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Colored gold
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Colored gold
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Ternary plot of different colors of Ag–Au–Cu alloys[1]

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,[2] 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:[3]: 118 

  • Alloys with silver and copper in various proportions, producing white, yellow, green and red golds. These are typically malleable alloys.
  • Intermetallic compounds, producing blue and purple golds, as well as other colors. These are typically brittle, but can be used as gems and inlays.
  • Surface treatments, such as oxide layers.

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%).[4]

Alloys

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White gold

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Main article: White gold
Rhodium-plated white gold wedding ring

The 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).[5] Like yellow gold, the purity of white gold is given in karats.

Rose, red, and pink gold

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"Red gold" redirects here. For other uses, see Red gold (disambiguation).
"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" redirects here. For the color, see Shades of rose § Rose gold.
Rose gold diamond engagement ring

Rose gold is a gold-copper alloy[6] 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.[7] 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:[4]

  • 18K red gold: 75% gold, 25% copper
  • 18K rose gold: 75% gold, 22.25% copper, 2.75% silver
  • 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 copper-rich alloys to change their color to reddish yellow or dark yellow.[3] 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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Main article: Spangold

Some gold-copper-aluminium alloys form a fine surface texture at heat treatment, yielding a 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.[3]

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.[3]

Green gold

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Further information: Electrum

Electrum, a naturally occurring alloy of silver and gold, develops a greenish cast with increasing silver content, ranging in color from green-yellow (for proportions of silver between 14% and 29%) to pale green-yellow (for proportions of silver between 29% and 50%).[8]: Fig. 2  It was known to the ancient Persians as long ago as 860 BC.[4] 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. 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.[9] Adding 2% cadmium to 18K red gold yields a light green color, whereas the alloy of 75% gold, 15% silver, 6% copper, and 4% cadmium is dark green.[3]

Gray gold

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Gray gold alloys are usually made from gold and palladium.[citation needed] A cheaper alternative which does not use palladium is made by adding silver, manganese, and copper to the gold in specific ratios.[10]

Intermetallic

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All the AuX2 intermetallics have the cubic fluorite (CaF2) crystal structure, and, therefore, are brittle.[3] 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.[11]

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.[11]

Purple gold

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Gold–aluminium phase diagram

Purple gold (also called amethyst gold[citation needed] and violet gold[citation needed]) 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[12]), as it is an intermetallic compound instead of a malleable alloy, and a sharp blow may cause it to shatter.[13] 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.[3]

Blue gold

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Blue gold is an alloy of gold and either gallium or indium.[13] Gold-indium contains 46% gold (about 11 karat) and 54% indium,[4] forming an intermetallic compound AuIn2. While several sources remark this intermetallic to have "a clear blue color",[3] in fact the effect is slight: AuIn2 has CIE LAB color coordinates of 79, −3.7, −4.2[11] which appears roughly as a grayish 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.[11]

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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For the colloquial term black gold, see crude oil.

Black gold is a type of gold used in jewelry.[14][15] 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.[3]

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.[3]

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,[16] 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.[17]

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.[3]

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.[3]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Colored gold

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from Grokipedia
Colored gold refers to alloys of gold with other metals that produce colors distinct from the natural yellow hue of pure (24-karat) , enabling a range of aesthetic options in jewelry and . These alloys typically contain 9 to 18 karats of for , with the added metals—such as , , , , , or —altering the through changes in electron structure and light absorption. The practice dates back over 5,000 years, with ancient civilizations like those in and using - () and - alloys as early as 3000 BCE to create varied tones for ornaments and artifacts. The most common colored golds include yellow gold, which is nearly pure gold or alloyed minimally with silver and to enhance strength while retaining a warm yellow tone; white gold, formed by alloying gold with white metals like (historically) or and , often rhodium-plated for brightness; and rose gold, a gold- (e.g., approximately 75% gold and 25% copper in 18-karat form) that yields a pinkish-red hue, popular in Russian jewelry from the onward. Less conventional variants encompass green gold (e.g., approximately 75% gold, 20% silver, and 5% copper for a greenish tint), gold (gold- or gold-gallium alloys, such as 46% gold and 54% indium, creating a brittle but striking ), purple gold (gold-aluminum , e.g., 79% gold and 21% aluminum, forming a sensitive amethyst-like ), and black gold, achieved through alloys with or iron or via surface treatments like oxidation, patination, or enameling. The color arises primarily from the ternary Au-Ag-Cu system for traditional shades, but modern explores compounds for exotic hues, though some colored golds remain too brittle for widespread jewelry use without stabilization. Purity in colored gold is measured in karats (e.g., 18K indicates 75% by weight) or (e.g., 750 for 75% ), ensuring the maintains 's hallmark resistance and luster while adapting to trends. These alloys not only expand possibilities but also influence properties like hardness and tarnish resistance, with historical examples like (73% , 27% silver) demonstrating early mastery of color manipulation in ancient coinage and . Today, colored dominates the global jewelry market, blending timeless appeal with innovative metallurgical techniques.

Fundamentals

Color Mechanisms in Gold

Pure gold exhibits its characteristic yellow color due to relativistic effects on the orbitals in its atomic structure. In heavy elements like , the high nuclear charge accelerates inner s to speeds approaching a significant fraction of the , leading to relativistic mass increase and contraction of the 6s orbital while expanding the 5d orbitals. This alters the energy levels, causing interband transitions that preferentially absorb blue-violet light (around 2.3–3.0 eV) while reflecting longer wavelengths in the and , resulting in the observed warm hue. When gold is alloyed with other metals, its color deviates from yellow through selective light absorption and scattering influenced by the mixed metal compositions. The introduction of alloying elements modifies the , lattice parameters, and , shifting the absorption edges in the . For instance, metals like silver or can broaden or shift the d-band to transitions, leading to altered reflectivity; this mechanism underlies color variations in alloys such as white or rose without forming distinct compounds. These changes arise from perturbations in the free electron gas and interband absorptions, where the complex function ε(ω) of the determines the wavelength-dependent optical response. Intermetallic compounds in gold systems produce distinct colors through the formation of ordered structures at specific stoichiometric ratios, which create new crystal lattices differing from the face-centered cubic structure of pure . For example, compounds like AuAl₂ adopt a cubic (CaF₂) structure, while others may form cubic or hexagonal phases, leading to unique electronic configurations and bandgap shifts that selectively absorb or transmit certain wavelengths. These stoichiometric phases enable vibrant hues, such as , by altering the in the lattice, distinct from disordered solid solutions. Surface treatments can modify 's apparent color without changing its bulk composition, primarily via or oxidation layers. Depositing dielectric thin films, such as , on surfaces creates interference effects where constructive and destructive interference of reflected light produces structural colors across the . Similarly, controlled oxidation forms ultrathin layers (e.g., Au₂O₃) that shift the effective at the interface.

Common Alloying Elements

Gold alloys are typically measured by the karat system, where 24 karat (24K) represents pure containing 99.9% or more , while lower karats indicate the percentage of relative to the total weight. For instance, 18 karat (18K) consists of 75% and 25% other metals, enabling the incorporation of alloying elements to alter color, hardness, and other properties without compromising the primary material's value. This system allows for a balance between durability and aesthetic variation in jewelry and decorative applications. To produce white gold variants, alloying elements such as nickel, palladium, and silver are commonly used, as these metals exhibit high and uniform reflectivity across the visible spectrum, particularly enhancing reflection in blue wavelengths to counteract gold's inherent absorption of blue light and resulting yellow hue. Nickel and palladium serve as primary whitener in many formulations, while silver contributes to a paler tone; however, nickel can cause allergic reactions in sensitive individuals, prompting the use of hypoallergenic alternatives like palladium or platinum in white gold alloys. Copper is a key alloying element for achieving red or pink tones in gold, as it promotes absorption of green light wavelengths, leading to the preferential reflection of red and orange hues that define rose or red gold. This effect ties into broader color mechanisms, such as selective light scattering and absorption influenced by the electronic structure of the alloyed metals. Silver additions to gold alloys produce greenish hues by increasing reflectivity across red, yellow, and green wavelengths in the Au-Ag-Cu system. For gray or effects, iron or may be alloyed with , though 's use is limited due to its , which can cause severe health issues including damage and fragility upon exposure. was historically employed in alloys for casting properties but has been largely phased out in favor of safer alternatives amid regulatory concerns. Intermetallic colored golds, such as blues and purples, often incorporate or , where precise ratios are essential to form stable compounds like AuIn₂ or AuGa₂ that exhibit these unique hues due to their crystal structures and electronic properties. Deviations from can diminish the color intensity, underscoring the need for exact composition control in production.

Alloy-Based Colored Golds

White Gold

White gold is an of combined with white metals such as or , designed to produce a bright, silvery appearance that closely resembles , making it a popular choice for jewelry settings and bands. The typical composition for 18 karat white gold, the most common standard, consists of 75% pure , 10-25% or as the primary whitening agents, and the balance made up of silver and to achieve uniformity and workability. These alloying elements, particularly and , reduce the yellow hue of pure by increasing light reflectivity in the . Originally developed in the early , white gold formulations initially favored for its cost-effectiveness and strong bleaching effect, but a historical shift toward occurred post-1920s in response to widespread allergic reactions to , leading to alternatives that are now standard in many markets. To further enhance its aesthetic appeal and longevity, plating is routinely applied after the is cast and polished, providing a brilliant white finish and added protection against scratches and ; without this plating, the can develop a yellowish tint over time as the layer wears. The incorporation of these whitening metals not only alters the color but also significantly improves mechanical properties, with 18 karat white gold exhibiting a hardness of approximately 200-250 HV, a marked increase from pure gold's 25 HV, which enhances for everyday wear. In the , white gold has achieved substantial market prevalence, commanding 39% of the U.S. market as of 2025, driven by its versatile, modern look in and fine jewelry.

Rose, Red, and Pink Gold

Rose, red, and pink golds are varieties of colored gold alloys primarily composed of gold alloyed with copper and often silver, creating a spectrum of warm, reddish hues prized in jewelry for their romantic and vintage-inspired aesthetic. These alloys derive their distinctive colors from the interaction of copper with gold, where copper's selective absorption of green wavelengths in the visible spectrum contributes to the resulting red tones. The exact shade depends on the proportions of the alloying elements, with higher copper content producing deeper reds and lower amounts yielding lighter pinks. A standard 18K rose composition includes 75% , 22.25% , and 2.75% silver, balancing durability and color. typically features even lower silver content and higher —such as 75% and 25% with no silver—for a more intense, deeper hue. In contrast, incorporates higher silver levels, like 75% , 20% , and 5% silver, resulting in a lighter, more subdued tone. Color gradation across these variants occurs with contents ranging from 15% to 25% in 18K alloys, shifting progressively from pale to deep as increases. The in these enhances strength but can lead to oxidation over time, forming a that darkens the surface. This susceptibility is somewhat mitigated by the addition of silver, which helps stabilize the and reduce the rate of copper oxidation. These exhibit a of approximately 15-17 g/cm³, lower than pure gold's 19.3 g/cm³ due to copper's lower compared to gold. Following its prominence in the , rose gold has experienced a modern revival, surging in popularity for its warm versatility in engagement rings and fine jewelry.

Green Gold

Green gold is an composed of , silver, and , with typical 18-karat formulations containing approximately 75% , 15-20% silver, and 5% , which imparts a subtle greenish tint through the formation of silver-rich phases and interactions in the Au-Ag-Cu ternary system. This composition leverages silver and to achieve greenish effects, distinguishing it from other colored . The greenish hue in green gold arises from the high silver content altering the alloy's , where the increased proportion of silver shifts the reflected toward pale yellow-green tones rather than pure , with enhancing the tint. In formulations that include minor amounts of , the color can be fine-tuned for a more pronounced verdant appearance, though the primary mechanism stems from the Au-Ag-Cu interaction in the . Green gold remains less common in contemporary jewelry compared to white or rose gold variants, often reserved for pieces evoking antique or historical styles due to its unique, subtle coloration reminiscent of ancient electrum. It finds application in ornate designs such as filigree work or enamel-compatible settings, where its pale green cast provides an elegant contrast. Lower-karat versions, such as 14-karat green gold with around 58% gold alloyed with higher silver and copper content, exhibit a more vivid green but are softer and less durable for everyday wear. During fabrication, green gold alloys containing and silver are prone to formation—a reddish-purple oxidation layer resulting from the interaction of and silver with oxygen at high temperatures—necessitating the use of protective fluxes during and to prevent surface discoloration. This issue can complicate processing, requiring careful handling to maintain the alloy's aesthetic integrity. In the 2020s, experimental formulations incorporated trace amounts of (around 2-4%) to produce brighter or deeper shades by enhancing the alloy's color saturation, though such additions have largely been discontinued due to cadmium's and environmental concerns. Modern practices favor safer alternatives like or to approximate these effects without health risks.

Gray Gold

Gray gold alloys are typically formulated as 18-karat compositions containing 75% by weight, with 10-15% iron, and the balance consisting of or silver to enhance stability and workability. The inclusion of iron produces a subdued metallic sheen resembling , achieved through diffuse that diminishes the alloy's inherent luster compared to yellow . Alloying with iron introduces significant challenges, primarily that complicates fabrication and increases the risk of cracking during processing. These alloys exhibit values ranging from 150 to 200 HV, providing improved durability over pure , though exposure to moisture can lead to iron oxidation and subsequent if not properly sealed. Since the 2010s, gray gold has found niche applications in men's jewelry, valued for its modern, matte aesthetic that complements contemporary designs such as bands and pendants.

Spangold

Spangold is a family of shape memory alloys composed of , , and aluminum, typically in 18- or 23-karat formulations with a nominal composition of 76% , 18% , and 6% aluminum. Developed in the late 20th century, these beta-phase alloys exhibit a distinctive spangled surface texture when subjected to controlled heating and cooling cycles, resulting from a martensitic phase transformation that creates faceted, iridescent patterns. The alloy's unique appearance arises from the reversible shape memory effect, where the material deforms under heat and reverts upon cooling, producing multicolored sparkling facets that shift under . This effect is exploited for ornamental purposes in jewelry, offering dynamic aesthetics not possible with traditional alloys. Historical production techniques for involve precise thermal processing to control the phase transformation and prevent defects. Spangold's applications are primarily in modern jewelry and , where its innovative properties allow for textured, lightweight designs. Due to the complexity of fabrication and higher costs, it remains a niche material, but advancements in have enabled its use in high-end artisanal pieces as of the .

Intermetallic Colored Golds

Purple Gold

Purple gold is a rare compound formed between and aluminum, valued in jewelry for its unique hue despite significant processing challenges. It consists of the stoichiometric AuAl₂, with approximately 79% and 21% aluminum by weight. This composition results in an 18-karat that qualifies for hallmarking in many jurisdictions. The compound forms through eutectic melting of the gold-aluminum mixture at 548°C, yielding a tetragonal responsible for its distinctive color by selectively absorbing yellow and green wavelengths of light. This color mechanism stems from alterations in the crystal lattice that shift away from pure gold's reflection. Upon solidification, the material exhibits a range of shades from violet to deep purple, depending on precise and cooling conditions. The of pure AuAl₂ itself approaches 1060°C, but the eutectic process allows formation at lower temperatures to minimize oxidation. Purple gold possesses exceptional , reaching approximately 300 HV on the scale, far surpassing that of traditional alloys, which enhances its for decorative purposes. However, this is accompanied by extreme , making the material prone to cracking and fracturing during cooling or subsequent handling. These properties restrict its applications to small-scale, non-wearable items such as inlays, enamels, or accents in luxury pieces where mechanical stress is minimal. First described in 1891, purple gold was synthesized in laboratories in the early and patented for use in , though early adoption was limited by its fragility, with the confirmed through analysis in subsequent studies. Commercialization for high-end jewelry emerged in the late , enabled by advances in controlled and techniques that improved yield and color consistency. Today, it remains prized for designs, though production is confined to specialized artisans.

Blue Gold

Blue gold refers to intermetallic compounds formed between and elements like or , producing a blue hue through bulk properties rather than surface effects. The primary compound is AuIn₂, with approximately 46 wt% and 54 wt% , resulting in a 10-12 karat . An alternative is AuGa₂, containing 58.5 wt% and 41.5 wt% , yielding a 14 karat with a subtler bluish tint. These compositions form narrow stoichiometric ranges, with deviations leading to multiphase mixtures that dilute the color. The intermetallics form via and solidification, with AuIn₂ having a of 541°C and AuGa₂ at 491°C, both lower than pure , allowing processing under controlled atmospheres to prevent oxidation. The color arises from the in the crystal lattice, which absorbs light in the red-yellow , reflecting wavelengths. AuIn₂ exhibits a deep, vibrant , while AuGa₂ shows a paler, grayish- tone. These compounds are brittle, though less so than purple gold, with hardness below 100 HV, limiting and making them susceptible to cracking under stress. AuIn₂ is the least brittle among them, enabling limited forming, but both are primarily used for non-structural applications like inlays or decorative elements in jewelry. resistance varies, with AuIn₂ showing higher stability than AuGa₂. Production requires precise alloying and annealing to achieve uniform color and minimize defects.

Surface-Treated Colored Golds

Black Gold

Black gold is created through surface treatments applied to a base of yellow , typically 18K, to achieve a dark, matte appearance without altering the bulk composition of the metal. The treatment modifies the surface to increase light absorption, resulting in a near-black finish that contrasts with the underlying gold's natural luster. This method distinguishes black gold from alloy-based colors, as the effect is confined to a thin outer layer. Common techniques include with or , applied in layers of 0.5 to 2 microns thick to produce a matte surface. provides a smooth, tarnish-resistant coating, while offers enhanced scratch resistance due to its hardness. Alternatively, controlled oxidation or patination uses chemicals, such as acids or sulfur-containing compounds, to form a black oxide layer on the gold surface, often resulting in a matte finish that is less durable over time. Another method is enameling, where black powdered glass is fused onto the gold using high heat (1,300 to 1,600°F) to create a shiny, glass-like black finish. Plasma-assisted (CVD) deposits or uses oxidation processes to form a ceramic-like finish, which scatters light for a deeper tone. Laser treatments include femtosecond applications to create surface nanostructures for a permanent appearance across the entire surface, while conventional laser methods are typically used for markings or engravings rather than providing full, uniform glossy coverage. These treatments are performed on 18K bases to ensure compatibility and durability in jewelry applications. Regarding durability, or plating typically lasts 6 months to 2 years under normal wear before fading, particularly on high-contact items like rings, requiring periodic re-plating to maintain the color. Enameling provides a more long-lasting finish due to its fused nature, though it may be susceptible to chipping. In contrast, controlled oxidation or patination can weaken the surface and fade more readily, while plasma oxidation, chemical oxidation, femtosecond treatments are more permanent, as they integrate into the surface without a separate layer that can wear away, though the resulting finish may be more brittle and prone to cracking under impact. Despite these limitations, black gold's surface modifications enhance its aesthetic appeal for modern designs. Black gold gained popularity as a trend in the , particularly for bands and men's jewelry, offering a contemporary alternative to traditional yellow or white gold. By 2025, it represents a niche segment in the black jewelry market, appealing to those seeking bold, edgy styles, with black bands noted as a rising choice among modern couples. The use of rare metals like and contributes to higher costs over equivalent yellow gold pieces, driven by material costs and specialized processing.

Blue Gold

Surface-treated blue gold is produced by electroplating a thin layer of onto a base of 14-18 karat , followed by to diffuse the indium and form the AuIn₂ compound near the surface, typically resulting in layer thicknesses of 1 to 5 μm. This method creates a bluish hue distinct from bulk blue . Controlled oxidation techniques can also produce blue tones on certain alloys, leveraging surface layers for color effects. Modern developments by jewelers in the late have focused on wear-resistant surface coloring. The resulting blue coloration in both techniques is superficial and prone to with everyday , exposure to chemicals, or abrasion, as the thin layer can over time. To enhance stability, a protective sealing layer is applied post-treatment, though reapplication may be necessary for prolonged use. Unlike blue gold, where contributes to bulk hues via the AuIn₂ compound, surface treatments provide optical effects without compromising the gold's . Primarily used for decorative inlays and accents in jewelry, surface-treated blue gold adds striking contrast to traditional yellow or white gold pieces without serving structural roles, as the color does not penetrate the base material. As of 2025, innovations in nano-coatings applied over treated surfaces have improved longevity by providing a barrier against environmental factors.

Applications and Uses

Jewelry and Ornamentation

Colored golds, particularly white and rose variants, hold a significant share in the U.S. gold jewelry market as of 2025, with white gold at 26% and rose gold at 31% based on combined preferences for their versatile aesthetics and durability. White gold, prized for its bright, platinum-like sheen, holds a 26% share in overall jewelry trends, while rose gold commands 31%, reflecting a shift toward warmer tones in bridal designs. In contrast, rarer intermetallic colored golds like purple and blue are reserved for bespoke jewelry pieces, where their unique hues add exclusivity to custom commissions, often limited to small accents due to production constraints. Cultural preferences shape the adoption of colored golds in ornamentation worldwide. In the , rose gold enjoys strong favor for its romantic blush, frequently combined with yellow and white in elaborate designs that symbolize prosperity and elegance. Western markets, particularly in the and , favor white gold for bridal jewelry, aligning with modern minimalist styles that emphasize clarity and sophistication. Green gold sees a resurgence in antique revivals, evoking Victorian-era opulence through pieces like ornate rings and pendants that blend historical motifs with contemporary wearability. Manufacturing colored golds presents notable challenges for jewelry applications, as their brittle nature restricts fabrication. For instance, gold's hardness and tendency to fracture limit its use in larger cast components, necessitating techniques like inlaying or for viable ornamentation. Rose gold's warm, copper-infused hue offers a softer alternative, enhancing its appeal in larger, more flexible designs without such constraints. Market dynamics further elevate colored golds, while a push for sustainable sourcing—intensified since —emphasizes recycled metals to meet ethical demands. Contemporary design trends in the highlight mixed colored golds, such as white-rose bicolor combinations, which create dynamic, personalized statements in rings, necklaces, and bracelets. These hybrids blend the cool elegance of white gold with rose gold's subtle warmth, aligning with 's embrace of layered, versatile ornamentation.

Industrial and Scientific Uses

White gold alloys, particularly nickel-free variants, are widely used in for fabricating biocompatible crowns and restorations due to their corrosion resistance and aesthetic similarity to natural teeth. These alloys, typically comprising with or silver, replaced nickel-containing formulations in the early 2000s to mitigate risks of allergic reactions, as was identified as a common in dental materials. Standards such as ISO 22674 ensure their , allowing safe intraoral use without eliciting in most patients. Intermetallic colored golds, such as purple gold (AuAl2), find applications in for plasmonic sensors owing to their unique electronic structure that supports . The vivid hue arises from selective reflection in the , with a minimum around 550 nm in the green region, enabling enhanced light-matter interactions for sensing biomolecules or environmental changes. colored golds exhibit plasmonic properties that have been explored for advanced optical devices and high-sensitivity detection. Black gold coatings, achieved through surface treatments like electrodeposition or nanostructuring, serve as efficient absorbers in systems, capturing a broader range of compared to untreated yellow . These coatings exhibit over 92% absorption across the , improving photochemical efficiency in solar cells by reducing reflection losses; recent studies indicate potential efficiency gains of up to 7% relative to standard interfaces in hybrid photovoltaic designs. Green and gray gold alloys, often incorporating silver and , are employed in for corrosion-resistant electrical contacts, providing reliable performance in harsh environments like connectors and switches. Their enhanced resistance to and oxidation, demonstrated in salt-spray tests outperforming traditional white golds, ensures stable conductivity in low-power applications such as semiconductors and circuit boards. These alloys maintain high electrical reliability without compromising the needed for processes. Ongoing research as of 2025 highlights advancements in nano-engineered for biomedical applications, particularly systems. Size-tunable nanoparticles, exhibiting colors from to based on plasmonic , enable precise conjugation with therapeutic agents for site-specific release in cancer therapy, improving and reducing off-target effects. These innovations leverage the and optical tunability of colored nanostructures to enhance imaging-guided treatments.

History and Cultural Significance

Early Developments

The use of colored gold alloys dates back to ancient civilizations, where natural and deliberate mixing with other metals produced variations in hue for aesthetic and practical purposes. In during (circa 2686–2181 BCE), —a naturally occurring of approximately 80% gold and 20% silver—was widely employed for its pale, white-like appearance in jewelry, amulets, and temple decorations, symbolizing divinity and eternity. also gold with to create redder tones, enhancing the metal's durability and visual appeal in artifacts such as beads and vessels from around 2000 BCE onward; this basic alloying technique allowed for controlled color shifts by adjusting proportions, with higher copper content yielding warmer reds. During the in the (circa 3000–1200 BCE), similar gold-copper alloys produced red golds for status symbols and trade items, marking early innovations in intentional color manipulation beyond natural deposits. Medieval saw further refinement of colored golds, particularly in the from 800 to 1400 CE, where gold alloys were crafted using techniques like and for jewelry such as necklaces, rings, and religious icons, blending functionality with artistic expression in a period of heightened goldsmithing expertise and cultural symbolism of imperial luxury and . By the , experiments in led to early forms of white gold alloys, including (a gold-zinc composition that whitens upon heating), developed around the for durable watch components and ornamental items, representing a shift toward engineered colors for mechanical applications. In the , roots of modern white gold trace to the 1880s, when the Belais brothers in New York began experimenting with nickel-gold alloys to mimic platinum's whiteness, culminating in patents in the that enabled broader use in jewelry despite initial brittleness issues.

Modern Innovations

The commercialization of white gold accelerated in the early , with the first German for a -- granted in 1912, enabling its introduction as a alternative in jewelry. In the United States, the Belais brothers received a key in 1920 for an 18-karat white gold formulation using , , , and , which became a standard for durable, pale-hued alloys. Following , manufacturers shifted from nickel-based white gold—due to rising concerns—to alloys, which offered better whiteness and without the health risks, a change solidified by the late as restrictions lifted. Advancements in intermetallic compounds expanded colored gold variants beyond traditional alloys. Purple gold, an intermetallic phase known for its brittle, violet hue, was first systematically synthesized and described in 1925 by chemist Edgar Wedekind through high-temperature reactions of and aluminum, though its jewelry use remained limited due to fragility. In the , blue gold based on the AuIn₂ compound emerged as a viable option, with VA Blue Gold SA commercializing a heat-treatable 46% -indium alloy in 1988 that develops a sapphire-blue at 1800°C, enabling applications in high-end pieces despite its hardness. Surface treatments revolutionized colored gold production by allowing color modifications without bulk alloying. Black gold plating surged in popularity during the 2000s, driven by techniques using or over yellow or white gold bases, creating matte, edgy finishes for contemporary jewelry that contrasted traditional shines. In the , electrochemical methods refined surface colors on gold, such as electrodeposition of thin oxide layers or analogs on gold substrates, improving durability and uniformity for decorative applications while minimizing material use. Sustainability efforts in production intensified in the , with increased of scraps from jewelry manufacturing to reduce demands and environmental impacts. Global recycled supply rose 12.5% year-over-year by mid-2025, the highest since 2020, incorporating colored remnants through advanced refining to maintain purity and color integrity. standards advanced via the EU REACH regulation's 2015 amendment to EN 1811:2011+A1, which updated the test method for the existing release limit of 0.5 μg/cm²/week in jewelry, prompting reformulations with or for safer, skin-friendly colored golds. Recent innovations include 2024 developments in processing for structural colors on surfaces, enabling customizable hues like iridescent blues and purples through nanoscale surface texturing without alloying or . This high-speed, one-step method, demonstrated on gold-graphene hybrids, achieves resolution below 1 μm and chromotropic effects, offering eco-friendly alternatives for precision jewelry and anti-counterfeiting. In cultural contexts, colored golds have symbolized status and divinity across eras; for instance, ancient Egyptian represented eternal life, while modern gold's resurgence in the reflects trends in and in global jewelry markets.

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