Plique-à-jour meaning “letting in daylight” in French is a type of enamel that allows light to shine through. In traditional enamel technique, a vitreous (glass-like) coating is fused on to a metallic base; whilst in plique-à-jour piece, the metal backing is removed so as to achieve the shine through effect. The resulting pieces are very similar to stained glass only on a smaller scale.

This vitreous enamelling technique was developed in the 6th century AD in the Byzantine Empire and is known for its highly complex and time-consuming production; each piece can take up to four months to complete with a high failure rate. However, the fragile nature of plique-à-jour makes it very rare to find pieces from the period before the 19th century. The technique was developed and subsequently lost in both Eastern and Western Europe. It was not until the late 19th century that the technique returned to popularity.