Comparative Hardness of White Metal Wedding and Engagement Rings

Comparative Hardness of White Metal Wedding and Engagement Rings
Above: MOH Hardness Scale of Alloyed Metals Used in Jewelry Production. Though this chart illustrates the relative hardness of metal on the MOH scale, there is some variance due to alloying.
In the comparative hardness of white metal wedding and engagement rings stainless steel is the hardest, followed by palladium and platinum.

Pendants, earrings and bracelets will last well if they are well made, regardless of the white metal chosen in the fabrication. But if you are purchasing a white metal wedding or engagement ring, its hardness and durability can be important considerations. To know the exact hardness of a particular ring in a jewelry store is, unfortunately, very difficult. Variables, such as alloys, used in a particular metal and their manufacturing process are generally unknown. Plus, the thickness of a ring and design may or may not impact the hardness of the metal, but they are certainly factors in a ring's durability over time. Still, we can draw some general conclusions as to the comparative strength of platinum, palladium, silver and white gold.

Gold and silver in their pure state are so soft that they can be shaped by hand. Even platinum and palladium, which are much harder than gold and silver, have to be alloyed to make them suitable for jewelry fabrication and wear.

How a particular precious metal is alloyed can be highly technical and proprietary. Both platinum and palladium wedding rings generally have 5% alloy mixed in with the fine metal. An 18K white gold wedding ring is 25% alloy while a 14K white gold wedding ring is 41.5% alloy. Fine silver is alloyed into "sterling silver" which has 7.5% alloy.

Technically, metallurgists measure hardness of metal on the Vickers scale, which tests the plasticity of metal against an indenter with a pyramidal diamond point. For our purposes here, using this approach is a tad too technically difficult. Instead, we chart the absolute hardness of precious metal on a MOH scale. At the bottom of the scale rests talc and at the top, diamond. Metals fall in between. A fingernail rests at the 2.5 hardness range, approximately the same hardness as gold and silver. A diamond rests at 10 on the scale.

Without alloy on the MOH scale, gold, silver and zinc are at 2.5; copper is 3; nickel 4; platinum 4; steel 4.5; palladium 5, rhodium is 6, and iridium and ruthenium are 6.5.


Those who are hard on their wedding rings would benefit from choosing from the toughest metals: stainless steel, palladium, platinum and 14K white gold. Eighteen karat gold and sterling silver can make fine wedding rings too, but they are more susceptible to dings and scratching. For other jewelry, any of the metals will generally hold up just fine.

The Impact of Alloy
As shown in the chart above, even small amounts of alloy can drastically change the nature of a particular metal. 14K or 18K white gold engagement rings are most commonly alloyed with palladium, nickel and silver and sometimes a small percentage of zinc. In the case of palladium engagement rings ruthenium is often used for 4.8% of the alloy, with trace amounts of copper or other components added to ease casting and fabrication. Platinum engagement rings are alloyed with iridium, rhodium and ruthenium.

Sterling silver is .925% fine silver. More often than not copper makes up the balance, which makes the silver harder, bringing it up to a 3 on the MOH scale. To resist corrosion, our stainless steel rings are made up of a mix of alloys, including chromium, molybdenum and nickel.

Once the alloys are added, the approximate MOH scale will be as follows. These should not be taken as exact numbers due to the variables mentioned above.

Sheer hardness is not the only thing to consideration in the purchase of a white metal wedding or engagement ring. Another factor is the ability for a metal to be stretched without snapping: tensile strength. Tensile strength is not necessarily proportional to how hard a metal is. Silver and gold are more plastic than platinum, palladium and stainless steel.

Yet, plasticity and brittleness are not necessarily correlated. If gold is banged against an unyielding surface it is more likely to crack while palladium and platinum may well only end up deformed. In addition, how the ring is made can certainly impact its hardness and brittleness. Casting a design is fairly straight forward, but in our studio we bang on the metals with a hammer, which hardens the metal considerably.
Repairs
Gold scratches and chips are relatively easy to repair, melting at a relatively low temperature, about half of that of palladium and platinum. Though gold can chip when scratched, it is a relatively forgiving metal and repairs easier than with platinum and palladium. However, when scratched, palladium and platinum tend to "furrow" rather than chip. The metal can simply be put back in place on a nonabrasive polishing wheel.

To conclude, the exact hardness of any precious metal used in jewelry can vary depending upon both its manufacturing and its alloy composition. The thickness of the ring and design can influence its durability. Also, sometimes metals are mixed on a single ring. In the case of our mixed metal, gold over silver, engagement rings are made with a sterling silver base and we generally use 14K gold for the mount because it is a stronger material than silver. Those who are hard on their wedding rings would benefit from choosing the toughest metals: stainless steel, palladium, platinum or 14K white gold. Eighteen karat gold and sterling silver can make fine wedding rings too, but they are more susceptible to dings and scratching. For other jewelry, any of the metals will generally hold up just fine.

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