A slide is a form of jewelry rarely seen today; it flourished in the 18th century but fell from favor with the vagaries of fashion.
Can't you just picture those majestic oil paintings of women in brocades and voluminous silks? The scooped and lace edged necklines called for all that lily white flesh of the neck to be adorned with a ribbon that often held an ornate jewel at the center.
Ribbons and bows were so popular, it is hard to find too many portraits of women from the period without at least one bow, in the hair, at the sleeves or neck, they were ubiquitous. When there wasn't a bow or ribbon, the jewelry often formed a styled bow as in this example.
Straight from that time period is this garnet and rock crystal silver slide. Threaded on a ribbon with a bow tied at the back of the neck, slide pendants such as this glittered in candlelight and most likely was worn in the evening.
Regal and radiant, almandine (purplish) garnets form flowers and foliate motifs. Rock crystal was faceted to resemble rose cut diamonds and set amid the bevy of color.
All are set closed backed in silver. Typical also of the period, the sculptural and rounded back is sensuous and tactile. All hand-made, the jewel possesses a dangle of more garnets and rock crystal.
This exact pendant is featured in the book, "Georgian Jewellery" by Olivia Howard Collins and Ginny Dawes on page 137. If you don't have it in your library, you should!