This portrait is painted in enamel on metal. The advantage of enamel over traditional miniature painting (watercolour painted on vellum or, from about 1700, on ivory) is that it does not fade when exposed to light. The process of painting with enamels is, however, less free than the miniature technique and is fraught with danger. The first colours to be laid on the metal support have to be those needing the highest temperature when firing. More colour is added and the enamel refired, the process ending with the colours needing the lowest temperature. Such labour meant that it was an expensive option.

Enamel was first practised in Britain in the 1630s by the Swiss goldsmith Jean Petitot at the court of Charles I. It was reintroduced around 1680 by a Swede, Charles Boit, although it had remained a hugely popular and fashionable medium in Continental Europe. This enamel of Charles I’s son, James II, was probably not by an English artist. James had become king of Great Britain and Ireland after the death of his brother, Charles II, in 1685, but was devoutly committed to reviving Catholicism in Britain. He was forced to abdicate in the Glorious Revolution of 1688, when the birth of his son, James Edward - later known as the Old Pretender - heightened fears of a Catholic succession to the throne. With the help of Louis XIV of France, James established a court in exile at St Germain near Paris, where he died in 1701. This enamel may have been painted abroad for the use of a loyal supporter in Britain.