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.

This enamel is by Jean Petitot, a goldsmith and jeweller. Petitot and his friend, the enameller Jacques Bordier, together developed the art of painting portraits in enamel using a previously unexplored range of colours and subtlety of tone. Petitot introduced the court of Charles I in England to this novel art in the late 1630s. It is likely that he left England before the execution of his patron, Charles I, in 1649. Thereafter he practised in France, painting many portraits of Louis XIV, his children and those connected with his court.

This is probably a copy of a painting, possibly by Robert Nanteuil (1623-1678), of Cardinal Armand Jean Du Plessis, Duc de Richelieu. The cardinal died in 1642 when Petitot was working in England, but this was probably painted after Petitot returned to France.