The game of marbles goes back to ancient Egypt. Then, and for many centuries afterward, the “marbles” were made of stone or were simply pebbles or nuts. Clay marbles were introduced in the Middle Ages, then crockery marbles in the 18th century. Because of their rather dull appearance, these aren't of great interest to collectors. It wasn't until the middle of the 19th century that glass marbles began to appear in any numbers. Originally, these were handmade by European glassblowers. Then, when World War I disrupted production, the United States transformed the market with machine-made marbles.
Look first at the condition of the marble. If it has lost more than a third of its surface area to chips and knocks, then it will be more or less worthless and attempting to price it will be a pointless exercise.
Check to see whether it is a handmade or machine-made marble. Machine-made marbles are totally smooth all over. Handmade marbles were originally snipped with shears from glass canes, and as a result they usually have two slight, swirl-like blemishes on either side, known as pontil marks. A marble with only one pontil mark is a so-called “end of day” marble, a one-off that a glassblower might have made as a gift for a child. Handmade and end-of-day marbles are older, less common and therefore more collectible than machine-made marbles.
Inspect the design of the marble. Marbles come in all sorts of patterns from the rudimentary to the elaborately worked. As a general tip, if the pattern looks as if it was the result of time and skill, then the marble is probably collectible. If it looks random, then it probably won't be of as much interest. One pattern in particular to watch out for is the “sulphide.” This is a clear marble with, sunk into its center, a small representation in white clay of an animal, person or building. Sulphides are by far the most rare and collectible of marbles. In design, marbles fall into into two categories -- opaques with the pattern on the outside, and clear ones with some form of embedded design within. However, there are many variations on this, and these variations have been given suitably colorful names such as the Cambroth, the Onionskin and the Peppermint Swirl. Definitions and pictures in the Resources may help you decide exactly what kind of marble you own.
Type an appropriate search term, such as “antique handmade Lutz marble,” into the search engine of an online auction sites. Skim through the results until you find a marble that closely resemble yours, then track it to its final hammer price. This will give you a realistic and up-to-date sense of what your marble is worth.