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 England 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, and achieved wide popularity with the work of Christian Friedrich Zincke of Germany. Both Boit and Zincke were goldsmiths by training. In the early 18th century a number of miniaturists took up enamel in order to offer their clients a choice. But as the market for all portraiture grew and as miniature painters worked on ivory with increasing confidence and bravura, enamel painters decided to learn their rivals’ art. In the 19th century the rich colour of enamel made it popular as a copyist’s art. This is a typical example of the taste for enamel copies. Like his father, Henry Bone, William made a successful living providing the public with such works.