Black gold is a more recent trend in the jewelry business. We are not talking about oil — also known as Texas Tea to vintage television fans – but that shiny valuable precious metal. If someone comes into your cash-for-gold shop looking to sell black gold, be aware. There’s no such thing. There is plenty of jewelry on the market that looks like it is made from black gold, and plenty of sellers on the internet advertising their black gold pieces, but black gold is not a natural metal.
There is gold that has been blackened, however.
According to Calla Gold, a jeweler located in Santa Barbara, there are four ways gold can appear black:
- Oxidation. Special acids when applied to the surface of gold cause it to darken or “oxidize.”
- Blackening. In blackening, a paint-like liquid is brushed onto the surface and worked down into the nooks and crannies. It’s polished on top to leave the recesses dark.
- Black enamel. Enamel is baked onto the surface of jewelry, much like similar liquids are applied to ceramic pieces. The result is a hard, smooth and shiny covering.
- Black Rhodium Plating. First let’s talk about Black Rhodium. Rhodium (Rh), number 45 on the Periodic Table, is a member of the platinum group metals (PGM). WebElements notes that Rhodium itself is a silvery white metal that was discovered by William Hyde Wollaston in 1803 in England. The origin of name is from the Greek word “rhodon” meaning “rose”. So if Rhodium is a silvery white metal, and is named after a rose, how can it blacken gold?
If you are searching the internet for how black rhodium is made, Calla advises to be aware that there are incorrect answers floating around, even on well-known authoritative websites. It was claimed by an online news article that black rhodium gets its color by adding ink to white rhodium. This is false.
Black rhodium does not appear in nature, but was discovered in a laboratory. Since it is a relatively new choice for jewelers, suppliers creating black rhodium use various different additives. Also note that it is not always black. Most of the time, it is a medium to dark grey and can darken towards black. It depends on what additives the supplier uses in their formula for black rhodium.
The recipes for black rhodium are proprietary and therefore are rarely talked about. Some of the possible additives for creating black rhodium can include tin sulfate, tellurium oxide and arsenic trioxide at very low percentages. Other possibilities include the use of ruthenium, also in the platinum metals group, as one of the additives and others use various chemical salts to create the grey to black color of black rhodium.
Now to talk about plating. In a normal plating process, jewelry is dipped in an electrolysis solution and the rhodium molecules adhere to the gold. (Calla Gold explained how to plate jewelry in this previous article How Gold Plating is Done, Step by Step.) The same online news article description of the ‘ink’ causing black rhodium to ‘bind’ to the metal is also false. Binding suggests a molecular bond which can be achieved in Physical Vapor Deposition, also known as PVD coating. In electroplating the surface covering of one metal on top of another is done and is topical, not molecular. This is why the PVD coating of watch bands lasts longer than the gold or rhodium or black rhodium electro-plating of a ring or chain.
Gold explains that Rhodium plating is similar to coloring your hair. The original hair color is not changed; the hair is simply covered with a fine layer of a different color material. In the same way, rhodium plating does not change the color of the base metal; it simply covers it with a different colored metal.
Gold goes on to say that “While a good hair dye and a good rhodium plating alike are meant to be long-lasting, neither is permanent. Both will fade and will need to be recolored in order to maintain the desired look. In the case of rhodium plating, you also have scratches and scuffs to worry about, which will expose the gold underneath.”
No matter if the scratch is there or not, the best way pawn shops, jewelers, and cash-for-gold operations can accurately assess if a piece of jewelry is made of real gold is to use an XRF precious metals analyzer. To be absolutely sure of the value of the precious metals you buy, use, and sell, x-ray fluorescence technology can be utilized as a fast, simple, nondestructive solution for gold analysis. You can measure the content of all gold and precious metals, as well as determine the presence and concentration of other trace, alloying elements, and dangerous heavy elements, which could impact health and the valuation of your pieces.
According to Gold, scientists have recently discovered a method for turning nearly any metal black, making black gold a reality. By using a high-power laser to focus huge amounts of energy on a tiny spot of metal, researchers are able to create microstructures that capture nearly all light that falls on the metal, turning it pitch black. Unfortunately, the process requires a very expensive femtosecond laser and access to huge amounts of electricity, so we don’t see that as a feasible solution anytime soon.
Editor’s Note: Calla Gold, owner of Calla Gold Jewelry, has been a Santa Barbara personal jeweler since 1983, specializing in custom wedding ring design, jewelry repair, ring resizing and antique jewelry restoration. Calla shares her tips and advice on the topic of jewelry regularly on her blog and social media. She is a contributor to MJSA (a leading resource in jewelry making and design). For more information on Calla Gold Jewelry, visit www.callagold.com