Background
The first glass marbles, according to a vintage edition of "Boys' Life" magazine, may have been made by the famous glass blowers in Venice. Even before glass marbles, though, marbles were made out of clay or stone during times reaching back thousands of years. The reason? To play. These handcrafted marbles served as toys that entertained as much as they pleased the eye. The mid- to late 1800s brought machine-made marbles onto the scene, and by the 1950s, marble-playing became a widespread pastime in places such as the U.S. and Germany.
Materials
Some other materials besides glass, clay or stone that have been used to make marbles include agate, limestone, wood, porcelain and, yes, marble. In the 1950s the "cat's eye" marble was first created in the U.S. by injecting colored glass into a plain-looking marble. For making glass marbles, the glass is melted and then pressed between two metal mold halves that form the marble's customary sphere shape.
Uses
While the marble is traditionally a child's toy, it's by no means limited to child's play. Marbles were created during World War II to serve as substitutes for certain steel bearings, which were hard to find at the time. These were, of course, hardened to withstand forces greater than what's typical during a game of marbles. Some fish hatcheries have even claimed that scattering marbles at the bottom of fish pools has produced better spawning results.
Looks
Beyond uses for function and fun, marbles also may be miniature works of art that draw gazes and dollars from collectors. Various factors influence which marbles are considered valuable and which are not. For example, marbles created by hand are more valuable, given that these are harder to make and usually are rarer. If the marble is bigger that 1-1/2 inches, then it's probably not handmade because of the difficulty of handcrafting a marble that size. Further, a marble created with brighter colors in a balanced, symmetrical pattern generally has more value.