The easiest way to identify an antique stoneware crock is through its salt-glazed finish, which is light colored with a grey tinge, rough and pebbled. Crocks that have the same salt glazing on the inside predate 1800, according to information from the Museums of West Virginia. Newer vessels are likely to be coated inside with a brown finish known as Albany slip.
Prior to the Revolutionary War, the U.S. Colonies imported all their stoneware from Europe. In the decades following the war, Americans established stoneware factories in New York, Pennsylvania and New Jersey. The designs on each piece of stoneware provide clues to its origin and age, according to antiques appraiser Dr. Lori. These can be decorative symbols or figures, often rendered with cobalt blue glaze.
Makers also stamped their crocks with their names or locations. For example, a crock bearing the stamp "Manhattan Wells" identifies its origins as Clarkson Crolius factory in New York, explains a Collector's Weekly article. A less common but just as collectible stoneware crock bearing a cobalt blue, hand-painted design might bear the mark "Adam Claire, Po'keepsie," which indicates the piece dates to the late19th century.
Dr. Lori points out that a more artistically rendered design on a stoneware crock is likely to raise the value of the vessel. Value also depends on age, condition and rarity of a piece of stoneware, so learning to identify such factors is essential to becoming a successful collector.