Salesman's cards would often have variations of the same button for buyers to choose from. These black glass buttons have differing tints.
Teeny tiny Czech glass buttons on original cards, c1920s. Buttons measure about 1/4". I imagine these trimming some gorgeous creation that flappers like Louise Brooks wore.
These were probably used in the very early 1800's, since the little card that these were attached to is over 50 years old.
Paperweight buttons refer to glass buttons that resemble glass desk paperweights, only smaller. These were first made in Europe in the mid 1800's. Most have a base with a preformed design & a cap of clear glass that covers from the top to the base. Some glass blowers would make these by building on the wire shank, adding the design & then the clear glass all while working over a flame to fuse them into a single piece of glass. Other glass blowers would insert the shank at the end of the process while the glass was still malleable & hot.