After further research, I don’t know if I entirely agree with this definition. The direct translation from French means “in slavery.”
The Antique Jewelry University website defines it as “Bracelets and necklaces in a style with plaques connected with multiple chains is called en esclavage.”
The website ADIN Fine Antique Jewelry gives this definition:
“Esclavage, French for slavery. A type of necklace composed of three chains or strings of beads or jewels in which the chains or strings hang approximately equidistant from each other. They were worn in Normandy as peasant jewelry in the mid-18th century.”
From the sold archives of One of a Kind Antiques .com was this piece:
The description also give a little history:
This definition is echoed on other sites such as the French blog, Jewelry and Precious Stones which posted several examples.
Roughly translated from the blog “The collar of slavery, in gold, was in the nineteenth century, the greatest gift a husband can give to his young wife, the Empire or the Restoration.
It usually consists of several chains in festoons, generally has three connected ovals, rectangular, glazed or not.”
This example is from BijouxAnciens:
Musées en Haute-Normandie has a nice piece in their collection.The term could certainly have been used for any manner of necklaces over the years evolving with fashion trends. In fact, contemporary examples tend to be of the fetish persuasion. Since words have different meanings depending on period and region, the example shown in class may very well be en eslavage but I believe the other examples above illustrate a more common usage of the term