Black gold
For the colloquial term black gold, see crude oil.
Black gold is a type of gold used in jewelry.[12][13] Black-colored gold can be produced by various methods:
Electroplating, using black rhodium or ruthenium. Solutions that contain ruthenium give a slightly harder black coating than those that contain rhodium.[11]Patination by applying sulfur- and oxygen-containing compounds.Plasma-assisted chemical vapor deposition process involving amorphous carbonControlled oxidation of gold containing chromium or cobalt (e.g. 75% gold, 25% cobalt[3]).
A range of colors from brown to black can be achieved on copper-rich alloys by treatment withpotassium 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's 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. Afemtosecond 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,[14] but this method is used in high technology applications rather than for appearance in jewelry.
Example.
Here’s an amazing & heavily studded 1.40 carat Diamond Engagement Ring Bridal & Matching Band Set stamped in 14k Black Gold. It features a Brilliant solitaire .45 carat round diamond set atop of the ring. It also comes with .95 carats of white round diamonds that surround the lovely center stone Halo style. The accent side stones are prong set circling the solitaire & down each side of the main ring. The stones are also prong set in one row on the top & the sides of the matching band. The sets top measures 10.8mm wide along the finger at its largest point. All of the diamonds are 100% natural, not enhanced or heat-treated. Unusual Engagement Rings Review
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