The Noble Rhodium
The precious element, Rhodium, belong to the noble metals of the periodic table. Noble metals like platinum, palladium, gold, and rhodium are durable, corrosion and oxidation resistant. It was discovered in 1803 in trace amount in platinum ore by William Wollaston. The ultra-rare silvery-white metal is most expensive metal in the world. It is extracted from platinum or nickel ores in conjunction with other members of platinum-family, alternatively Platinoids or Platinides. The tarnish-resistance of this group is what makes it suitable for jewelry.
Rhodium plating is feasible compared to solid rhodium jewelry as the metal has very high melting and boiling points. This makes it difficult to mold it into jewels. Also the metal is rare in nature. It is refined from the ores of other metals i.e. nickel, platinum. This induces an uncertainty in its prices, making it an expensive metal than gold and platinum. Hence, doesn’t make for a desirable investment choice. The shiny metal, however, is highly reflective and gives jewelry a luxuriant white finish when plated with Rhodium.
The process of coating the jewels or precious metals with Rhodium is called rhodium plating or rhodium dipping. An extremely thin layer of rhodium is applied on the jewelry. Silver metals as silver sterling, palladium, and white gold, are preferred for rhodium plating. Rose gold is not plated with rhodium unless a change of color is desired.
Electroplating method is used for rhodium plating. It is a process in which one metal is coated on another through electro-deposition process. The jewelry to be plated is “Electro-cleaned” thoroughly especially crown settings. This is important as dirt particles interfere with the process of electroplating. Cleaning with steam and distilled water is also practiced.
After this, the jewelry is dipped in rhodium solution (rhodium concentrate and water). The concentrate is adsorbed or fused onto metal via electric charge. A very thin layer, ideally 0.75 to 1.5 microns (thinner than the human hair i.e. 100 microns) is plated on a ring. Plating beyond these limits would either cause discoloration (thin layer) or brittleness (thick layer).
The detailed process for rhodium electroplating is as follows;
- Put the magnetic stirrer in a glass beaker and Pour 1litre of rhodium concentrate.
- Place it on magnetic stirrer hotplate for heating at 100 degrees Fahrenheit for 15 minutes.
- Connect the anode (positive electrode) with rectifier set at 4 to 6 Volts and plating time of about 45 seconds. Dip the anode in the beaker. You’re all set for rhodium electroplating.
- Use a 4″ piece of copper wire (acts as cathode or negative electrode) to hold the item. Connect it to the negative end of the rectifier.
- Rinse the jewelry with distilled water or electro-clean.
- Place in acid activation beaker for 10 seconds.
- Rinse again with distilled water.
- Electroplate in rhodium concentrate for 40 seconds at preset conditions.
- Rinse again with distilled water.
- Electro-clean for 10 second to stabilize the plated layer.
- Rinse again with distilled water and dry using a hair dryer.
- Acid activation and Electroplating solutions can be reused for a week.
In case of re-plating, polish the jewelry first. Make sure to remove the polish so it does not contaminate the electroplating. As the plating solution involves toxic sulfuric acid in it. Acidic fumes are produced during the plating process. These fumes are harmful for human health. Therefore, the process must be performed with PPEs and properly ventilated room.
Rhodium Plating in Jewelry
The rhodium plating of the jewelry is quite common these days. The process usually cost between $50 and $150, as the raw material (rhodium concentrate) is quite expensive. This is done so;
- To change the color of gold jewelry
- To improve the reflectivity and shine of the jewelry
- To prevent the blackening of the skin from the gold jewels
- Enhance strain-resistance of the metal
- Best silver-white alternative for those allergic to silver
Rhodium Plating changes the Color of Gold
Rhodium plating is a common practice with gold jewelry. The mined gold is yellow-orange in color. To enhance the durability of the pure and soft-gold, it is alloyed with other metals. Most commonly it is alloyed with copper, nickel, or platinum. These alloys not only increase the durability of the metal to make jewelry, but also change its color.
So if you are thinking you can mine the rose gold or white gold out of the ground, you are wrong. Pure gold is alloyed with copper and silver to give a rosy pink color. For the white gold, it is alloyed with silver-metals. Alloying with white metals change its color, but it is impossible to lessen the yellowish hue without decreasing the gold content of the jewelry.
To convert it into “White” gold, it is bleached and then alloyed with white metals i.e. nickel. But the pairing outcome isn’t perfect white. Rhodium plating the jewelry gives it the platinum-white color. It also increases durability and gives it a lustrous white sheen. The process can be reversed by mechanically polishing it off original yellow shade.
Rhodium Plating prevents the Blackening of Skin
Gold is a relatively soft metal compared to silver or platinum. It is alloyed with different metals to enhance its durability. Alloying with metals affects the quality or purity of the jewelry. 14karat gold is only about 58% pure. Remaining sum can be attributed to the alloys. These alloys are reactive and leave a black smudge on your skin.
The reaction can be due to many reasons or factors i.e. moisture, pH, chlorides etc. (link to why does my gold ring turns my finger black?)That’s where rhodium plating comes into play. Plating the jewelry, particularly rings create a protecting barrier between ring and the skin. Also, prevents the corrosive reactive of the metal alloys. Hence, instead of compromising on the quality of the jewelry with gold content, you can always plate the jewels with rhodium. It gives them a reflective luster, masking the yellow hues completely as well as enhanced scratch-resistance.
Rien n’est Eternel
Thinking about how long would it last? There’s a French phrase; “Rien n’est éternel”. This means “Nothing Last Forever” Same is the case with Rhodium plating. It is the infusion of one metal over another. Hence it is bound to wear off. And that depends on how often you wear it or how much you shield your jewelry, particularly rings from wear and tear? Also depends on the thickness of the plated layer.
For other jewelry accessories, like earrings or necklace that are worn occasionally, it may last for years as they don’t get rubbed off against abrasive surfaces. The rhodium plating of the wedding bands or broaches, on the contrary, might wear off within a year. When the metal starts transitioning to its original yellow hue in patches or loses its luster, it is high-time for re-plating the ring.
It is an established fact that jewelry needs rhodium replenishment after some time. Usually after 12 to 24 months depending on its usage. But if the rhodium goes away earlier than expected, you need to have it examined from an expert jeweler. There’s a chance that the rhodium plating layer of the ring is too thin to sustain the bright luster for longer.
Also, avoid rubbing the jewels against any surface or wash your hands wearing rings. Such activities increase the risk of wear and tear. It is better to use gloves or remove the jewels before work. Furthermore, keep the jewels clean and dust free. Even the fine dust particles or makeup products can cause abrasive damage to the jewels. Jewelry can be cleansed with a jewelry cleaning solution or soapy solution. Care must be taken while cleaning the rhodium plated jewels. To wrap it up, rhodium plating gives the jewelry a lasting (but not ever-lasting) bright sheen, prevents corrosion, and is nonreactive. It is definitely worth the investment.