How can I test if a metal is platinum?

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Category: Metallurgy

Subject: How can I test if a metal is platinum?

Question

Are there simple tests to identify platinum?

Answer

The simplest tests are heating and discoloration.

If the item is heated, for example, in a Bunsen flame, platinum will be more difficult or impossible to melt and the platinum will not discolour.

The effect of acid is another basic test. None of the common acids will attack Pt. However, cold aqua regia (3 part HCl + 1 part HNO₃) will attack Pt, but only very slowly. Aqua regia will attack most other metals and alloys almost instantaneously. A reputable jeweller should be able to test for platinum using acid.

If these two tests are not feasible then find the density of the object. This will identify Pt from silver-coloured base metals.

To measure density:

Find the mass of the object (in grams) and find its volume by the volume of water it displaces (in cubic centimetres). Divide the mass by the volume to obtain the density (grams/cubic centimetre).

This value can then be compared with known densities of the platinum, generally accepted as 21.45 g cm^–3. Other physical and chemical properties can be found by searching one of the online databases.

Lastly, a piece of platinum jewellery will always bear a legal hallmark.

Answer posted November 2004

Submitted by: Ms Susa Ashton

Answered by: Robert McGrath

Affiliation: Johnson Matthey Noble Metals