Gold, Silver, Platinum and Palladium are rarely used in their pure state. They are usually alloyed with other metals to make them more workable and durable.
The four rings below are cast from the same mould but made from different metals, 925 (sterling) Silver, 750 (18ct) white gold, 950 Palladium and 950 Platinum.
Their weights vary from 3.9 grams to 8.0 grams and the current UK retail from £40 to £1200 at current prices.
Without a hallmark it is very difficult to tell which is which, offering a profitable opportunity to mis-sell them.