To identify antique stoneware markings, people should first determine what letters or numbers the mark consists of and then look the mark up on the website of an auction house, such as Crocker Farm, Inc. It may also help to contact the auction house and ask for a free cursory evaluation of the stoneware. Another way is to search the mark in a book on antique stoneware, such as "Decorated Stoneware Pottery of North America" by Donald Blake Webster.
Determining the mark on the stoneware correctly is crucial for a successful search. If some parts of the mark are difficult to identify, it may help to examine the piece of stoneware in a different light. A mark may look much more clear in the sunlight than indoors. In addition, it may help to use a bright light angled parallel to the surface of the stoneware piece.
Another way to determine what the mark says more accurately is to place a piece of paper on top of the mark and trace it using a pencil. The result on the paper might be more readable than the mark in the clay. If only a part of the mark is visible after tracing, try performing a search using that information.
There are many books that help to identify antique stoneware marks. It is helpful to look in books specific to the region where the piece comes from.