Art is not jewellery. Its value does not reside in the price of the materials from which it is made. After all, the cost of the pigment, oil and cloth that made up a Rembrandt was negligible. It’s what he did with them that counts. On the other hand, spectacular works of art can be made from gold and gems, as is clear from some — if not all — of the items displayed in the new installation of the Waddesdon Bequest at the British Museum.