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 of whom were goldsmiths by training. In the early 18th century a number of miniaturists took up enamel in order to offer their clients a choice.

James (Giuseppe) Macpherson was the son of Donald Macpherson who had been a servant to Alexander, 2nd Duke of Gordon (1678?-1728). Accompanying the duke on a visit to his friend, Cosimo III, 6th Grand Duke of Tuscany, Donald Macpherson had settled in Florence. Giuseppe was born there on 19 March 1726 and became a pupil of Pompeo Batoni in Rome, but as well as painting in oil he made a name for himself in the early 1740s as a miniature painter. Enamel painting was an internationally popular and fashionable art and it was commercially astute to be able to offer this alongside his oil portraits. Macpherson worked in Milan and Paris, London and probably in Germany, painting miniature portraits of European rulers, princes, ladies and gentlemen, and making copies of celebrated pictures from famous galleries.