These large tiles are then set into a solid back ground such as sandstone or black marble for a pictoral effect. The surface of the design is flush with no protruding tiles or grooves between the tiles.
Floral scenes are the most common, but any design can be used, such as butterflies, human figures, birds and architectural buildings.
The settings are generally silver or genuine gold, but plated settings and brass are also used. Most settings are open backed to show the back of the background stone used.
The popularity of Pietra dura pieces dates from the early to mid 1800s. This type of souvenir jewelry is known as "Archeological Jewelry." Mosaic jewelry of all kind became fairly widely available after the excavations of Herculaneum and Pompeii.
Pietra Dura jewelry was found in Italy - especially Florence, but was also available around the same time in England and other European areas. I've also seen some examples of it in pieces from Taxco Mexico.
This type of mosaic jewelry is highly collectible and fuels much of the tourist trade today in Italy.
Photos are courtesy of ebay sellers anteaklovr, clelak and Adin Fine Antique Jewelry and vintagejewelrylane.com