Clay marbles were produced extensively in the 1800s and 1900s. They were popular because they were inexpensive to produce, requiring none of the special equipment or knowledge necessary for the production of glass marbles, which made them inexpensive to purchase.
Material
Clay marbles were made of several different types of clay, with different densities and glazes. Because they were often made of local clay and imperfectly made, they were not highly valued when they were being produced.
Eye Appeal
Eye appeal is one of the factors that determines the value of marbles. Clay marbles do not usually have the eye appeal of glass, agate or porcelain marbles, so are valued less.
Rarity
Marbles that are more rare and difficult to find are valued higher than more common marbles. Because clay marbles were produced so prolifically they were referred to as "commons" or "commies." These clay marbles are still relatively common, which reduces their value.
Condition
Marble condition, the number of chips or cracks in it, affects the value of it. Clay marbles were often glazed or painted, which makes the clay marbles more susceptible to damage than other marbles.
Size
The larger a marble is, the more it is worth, no matter what material it is made of.