Density of platinum

The density of platinum is 21.45 grams per cubic centimetre. As a comparison, the density of gold is 19.3 grams per cubic centimetre. Platinum is therefore one of the densest precious metals, followed by gold, palladium, and silver.

Like gold then, the intrinsic density of platinum is part of what makes it so appealing. Holding even a small amount of platinum in the hand conveys the impressive weight that might not be expected at first glance.

Density can be defined as the ratio between an object’s mass and volume. Scientifically, this would be the 'unit mass per unit volume' and is usually quoted in grams per cubic centimetre – g/cm ³ .

To get technical, density is also sometimes known as ‘specific gravity’; which is a unified ratio of density within water. Platinum’s specific gravity is 21.4. Simply put, this means you would need more than 20 times the equivalent volume of water to have the same weight in platinum.

The density of platinum

Similar to gold, despite having a high density, fine or 99% platinum is soft and easily damaged. For practical use it is usually hardened by mixing with other metals. Iridium, rhodium, ruthenium and palladium are commonly used as alloys, and each can have their own effect on the density of platinum.

5% ruthenium is the preferred alloy of choice for many high-end manufacturers. The resulting hardened alloys still have a bright attractive lustre, and do not tarnish, but vary slightly in colour.

Platinum alloys are classified in terms of parts per 1,000. In this, millesimal, system pure platinum is 999. Depending on the metal used, platinum alloys will typically have slightly lower densities than fine or 999 platinum. This is due to most of the metals being used having a lower density than platinum.

In the UK, since January 1st, 1975, there has been a legal requirement to hallmark platinum. From 1975 until January 1st, 1999, the only officially recognised standard was 950 parts per thousand. Since then four more standards of 850, 900, 950, and 999 have also become recognised. Despite this, the majority of jewellery is still made in 950 fineness.