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 was formerly attributed to 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.

Petitot was much imitated in his day, and has been even more frequently copied, especially in the 19th century. But this seems to be an authentic early 17th-century work which has simply been misattributed to Petitot in the past. It is possibly by a contemporary of Petitot and as such is an interesting if puzzling object.

Frederick V (1596-1632) was elector Palatine of the Rhine. He was also made king of Bohemia (1619-1620) and was head of the Protestant union against Catholic Austria in the Thirty Years' War (1618-1648).