Plique-à-jour (French for "letting in daylight"), is a technique where the enamel is applied in cells and the backing is removed in the final stage of work so that light can shine through the transparent or translucent enamel. In essence it is a miniature version of a stained glass window and is very difficult and extremely time consuming to execute. Which makes its beauty all the more desirable and special in a piece of jewelry.

The technique was developed in the Byzantine Empire in 6th century AD. Western Europe adopted the plique-à-jour technique during the Renaissance with famed sculptor and goldsmith Benvenuto Cellini (1500–1571) describing the process in his treatises on goldsmithing and sculpture in 1568 and then the technique was seemingly lost again.

It was re-discovered in the late 19th century movement of revivalist jewelry, and became especially popular in Russia and Scandinavia and in countries where the Art Nouveau movement emerged including France, Belgium and Germany. Artists like René Lalique and his contemporaries used plique-à-jour extensively in jewelry creating small masterpieces to wear.

To be found in the Lang Antiques Collection are many wonderful jewels with plique-a-jour enameling ranging from early twentieth century pendants accented with this enamel, to a butterfly brooch with transparent enamel wings. Several dramatic Egyptian revival brooches are available as are other beautiful examples of this intriguing technique.