The Button Collector’s Encyclopedia, page 145
PASTE – This hard bright glass, often called rhinestone, is cut similarly to the way diamonds are cut, and is used in the same manner. Paste does not have the power of reflecting from the interior as diamonds do, and therefore foil is placed on the back of each piece. The paste used in decorating 18th century buttons was put in sunken settings with cuplike indentations; later, prongs were used to hold the paste “stones” in place. Occasionally, button collectors refer to this material as “strass.”
The Big Book of Buttons, page 154
…although the vast majority of “jeweled” buttons are set with glass-paste or imitation gemstones, there are a very few which are set with genuine jewels.
Examples of jeweled buttons, real or imitation, from the 18th century are, predictably, very fine. Glass, or sometimes rock crystal was cut and facetted as carefully as real gemstones and mounted over foil in silver or silver plate cup settings. Sometimes the stones were held in depressions in the metal setting by tiny grains of silver. Claw settings are usually found on nineteenth and twentieth century buttons only, but finer examples of later jeweled buttons may have grain set stones.
The Complete Button Book, page 4
…. Many of the buttons produced during the pre-Revolutionary period in France were extremely valuable in terms of the gold, silver, gems, and other precious materials used in their construction. The ease with which the stones could be removed, the metal melted, and a handsome sum received for both, has probably caused the destruction of many of these luxurious buttons.
The imitation gem buttons of the period have survived in far greater quantities. For centuries man had used colored glass or enamel to imitate precious stones, but he did not succeed in making a reasonable facsimile of a diamond until the eighteenth century. Strass, or paste, has been used in the manufacture of buttons since its discovery. A good rule to remember in attempting to date strass is the fact that in eighteenth century buttons the stones are usually sunken in lower mountings with small grains of metal used to hold them in place.
From Diana Epstein'sThe Button Book, page 118
The glamorization of the Duchess of Windsor’s jewels along with fashion designer Coco Chanel’s embrace of costume jewelry led to widespread use of rhinestones in designs of the 1930s and 1940s.