People often hear about the Mohs scale of hardness when it is used to compare gemstones, but this system is also used to rank metals. Let’s see how the scale of metal hardness can be useful to you and how the metals used in jewelry compare on it.
What Is the Mohs Scale?
The Mohs scale is a system used to rank materials on their hardness, which is graded using numbers from 1 to 10. It can be used to compare gemstones, metals and other materials, and evaluate their relative durability.
To use an example, one of the hardest substances on earth, diamond, is rated 10 on the Mohs scale, while plastic and pencil lead, for instance, are on the other end of the scale, with a hardness grade of 1.
The Mohs Scale of Hardness for Metals
Here is a list of the hardness grades for some of the metals that you are most likely to come across in your everyday life, especially when dealing with jewelry:
- Lead: 1.5
- Tin: 1.5
- Zinc: 2.5
- Gold: 2.5-3
- Silver: 2.5-3
- Aluminum: 2.5-3
- Copper: 3
- Brass: 3
- Bronze: 3
- Nickel: 4
- Platinum: 4-4.5
- Steel: 4-4.5
- Iron: 4.5
- Palladium: 4.75
- Rhodium: 6
- Titanium: 6
- Hardened steel: 7-8
- Tungsten: 7.5
- Tungsten carbide: 8.5-9
Why It Is Important to Know the Hardness of Metals
When the German geologist Friedrich Mohs devised the scale of hardness that we use today, he used a simple principle to determine the grade for each material: Which materials can scratch it, and which materials it can scratch.
For example, platinum, which has a hardness of 4-4.5, can be scratched by all materials that have a higher Mohs grade (such as topaz, which is graded 8), and it can in turn scratch any material that is graded lower (e.g., gold, which has a hardness of 2.5-3).
As you can see, where a metal stands on the Mohs scale can give you valuable information as to which other metals can scratch it. This is very useful to know when deciding which pieces of jewelry you shouldn’t store in the same box and which items you can wear together. It can also help you determine which jewelry will be more durable just by knowing the metal it is made of.
How to Use the Metals Hardness Scale
The Mohs scale of hardness can be useful when you are shopping and debating between pieces of jewelry made from different metals. By looking them up in the metals hardness table, you can see which option will give you better durability, and you can then decide if the price asked for it is worth it to you.
For example, platinum is much more durable than silver, and in general, harder metals last longer when worn. However, platinum is also much more expensive, so you should think whether you are willing to pay a premium for the additional durability.
Metal Hardness and Alloys
The Mohs grade for each metal denotes its hardness in its pure state, i.e. without any other materials mixed in. However, in reality, almost all metals used in jewelry are combined with other metals to make the resulting material more durable or cheaper.
For example, gold is often mixed with nickel, zinc, copper and other metals to make it harder. Similarly, tungsten has a hardness of 7.5 when pure, but when carbon is added, tungsten carbide is created, which has a hardness of 8.5-9 on the Mohs scale.