Originally made up of little glass bricks called "tesserae", Roman mosaics were packed with as many as 1,500 to 5,000 pieces per square inch. Buttons of this style were very popular with Victorian purchasers in the mid-19th century.
Later, two other types of Italian micro mosaics were developed. Florentine "pietra dura" (hard stone) and Venetian mosaics used thin bits of stone carved into specific shapes fitted together inside of square or rectilinear tesserae.
The resultant buttons, made of bits of malachite, carnelian and quartz, depicted flowers, birds, butterflies and the like in beautiful color gradations.