Is Platinum a Good Choice for Jewellery?

Editor’s Note:  We have written about the Platinum Group Metals (PGMs) before, and explained how they are a family of six structurally and chemically similar elements that are most valued for their wide range of industrial, medical, and electronic applications.

Today we will be discussing Platinum (Pt) itself, which has a high melting point and temperature stability, is highly corrosion oxidation resistant, and it is a good oxidation catalyst.  It is most recognised as a metal used in catalytic converters, electronics, and in jewellery.  Today, our guest writer, Calla Gold, writes about the use of platinum in jewellery.

Why Platinum Jewellery Turns Dull So Fast

By Calla Gold

Platinum is not a hard metal. It is 4 – 4.5 on the MOHs scale of hardness. This means it can be scratched by anything harder than it is. Diamond is ten on the MOHs scale and can easily scratch platinum. An amethyst is a seven on the MOHs scale and can scratch platinum.

For comparison, pure gold is 2.5, on the MOHs scale. That’s about the same hardness as your fingernail. That will not work for jewellery making. When white gold is prepared for jewellery making, by adding alloy metals, for example at 14kt or 58% pure gold, its hardness gets bumped up to 3.5 – 4.  That looks about the same as platinum. But it’s not just the hardness that determines how your metal will wear and look over time. What the MOHs scale doesn’t show you, is the way your chosen metal reacts to harder obstacles when they collide.

Platinum is more dense than gold. The same amount of platinum weighs 60% more than gold. This is because on a molecular level there are more and smaller molecules packed into that little bit of space in platinum. Platinum’s density allows it to be used in a purer form than gold. This density translates to strength. But, that does not make it a super hero.

Platinum is also a soft metal. When it gets a scratch or a micro-dent, it is actually moving out of the way of the harder item to which it is colliding. By softly yielding and getting micro-dents to a state where no part of the surface hasn’t moved, the platinum becomes dull.

To compare, 14kt White gold, which has been alloyed with stronger metals to make it into jewellery and make its normally yellow colour white, becomes a harder metal than platinum. If banged against a hard surface, the white gold can leave a tiny bit of itself behind on the harder surface and show a scratch on its surface. The scratch will be very thin as the hard metal resists the harder surface. The platinum band scraping against the same surface moves, and its scratch may look a bit deeper. This is because the metal is softer. Its response to the surface is to yield, to get out of the way. But because of its density, it does not leave a bit of itself behind.

The final effect is that white gold, though it may have many fine scratches, is still shiny – while platinum will become dull.

Some people have trouble telling the difference between white gold and platinum, but as you can see there is a big difference.

The best way to accurately assess if a piece of jewellery is made of gold or platinum (or some other material) is to use an XRF precious metals analyser. This X-ray Fluorescence technology can be utilised as a fast, simple, non-destructive solution for precious metal analysis. You can measure the content of all gold, platinum, and other 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 the pieces – not to mention how shiny or dull they may become.

Source: Thermo Fisher Scientific – Analyzing Metals

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