In its strict sense, the word ‘miniature’ describes a technique of painting in watercolour rather than the size of a painting. Miniature painting developed as a separate art in the 16th century and in Britain it became predominantly a portrait art. In Continental Europe, however, the taste for portraits small enough to be carried on the person was often met by artists working within very different artistic traditions. One type of ‘miniature’ (as all such small works are now known), produced more on the Continent than in Britain, was the oil miniature, usually painted on metal. Most of these oil miniatures are anonymous, since the art of painting small portraits in oil on metal was not one in which leading artists specialised. More often it was part of a repertoire of portrait styles offered by less well-known oil painters.

This oil miniature is unusual in that it is by a named artist working in England. John Zachary Kneller was born in Lübeck on 6 October 1644 and was the brother of Sir Godfrey Kneller, with whom he came to England after travelling in Italy. John Zachary painted mostly architectural decoration and still lifes. The market for his miniature works in oil relied on his brother’s successful portrait business as they were mostly small, portable copies of Sir Godfrey’s portraits. He died at Covent Garden in 1702.

This is a portrait of King William III, who reigned from 1689 to 1702. He was born in the Hague in the Netherlands in 1650 and died in London in 1702. William, Prince of Orange, became stadholder (governor and commander in chief) of the United Provinces of the Netherlands in 1672 and married his cousin, Mary Stuart, in 1677. When his father-in-law, James II, was driven into exile in 1688, William became king of England, Scotland and Ireland. He ruled as joint monarch with his wife, Mary II.

One problem with oil miniatures, which probably became apparent quite quickly, is that the varnish often discolours, which results in a darkened effect, as seen in this oil miniature.