Imagine a rosary-bead maker watching a fish being scaled in a basin of water. The water has colorful, pearly reflections which seem to form as the fish scales dissolve. The bead maker then gets the idea to filter the water, recover the pearly substance from it and mix it with a kind of varnish. Later he coats the inside surface
of a hollow glass bead with the pearly mixture, fills the bead with wax, and what's the result? The birth of the modern-day imitation pearl.

This occurred in France in the 17th century. Jacquin was the name of the rosary-bead maker. And essence of orient (or pearl essence) is the name of the pearly mixture he discovered. Today, the finest imitation pearls usually have several coats of essence of orient.