Strictly speaking, this enamel is not a miniature. A ‘miniature’ in the 18th century was specifically a painting in watercolour on ivory. The techniques of enamel painting were first perfected in the early 17th century on the Continent by goldsmiths. Enamel is a type of glass coloured by metal oxides and fused to a metal base by firing in a kiln. Each colour has a different melting point, and so must be applied and fired individually. To achieve a work of sophistication, many applications and firings are required, and careful calculations are needed to avoid accidents in the firing process.

Like most early 18th-century English miniaturists, Spencer taught himself the art of painting in watercolour on ivory. As enamels were fashionable at this time, he also learned this complex art, apparently without any lessons. The memoirs of Spencer's fellow miniaturist Samuel Finney describe how clients often ordered a portrait both in miniature (watercolour on ivory) and in enamel. Unlike miniatures at this time, enamels were richly coloured, and they were additionally tough and durable and could be worn without the risk of fading or damage.

This enamel is no longer in its original frame. The costume and pose of this unknown woman are copied from a miniature by Jean Etienne Liotard, who worked in Turkey for many years. At this date in Britain, Turkish dress was popular as masquerade costume, and Liotard's costume can be seen in a number of portraits of different sitters.