Identifying antique plates is like detective work: You sift through the clues to solve the case. After you do a little homework, you'll find many clues on plates easy to interpret. For example, if you see the word "royal" attached to a company's name, the plate was probably made after the mid-19th century. If the country of origin is stamped on, the plate most likely dates from the 1890s or later.
Read to familiarize yourself with the field. Pick up a book such as "Kovels' New Dictionary of Marks: Pottery and Porcelain, 1850 to the Present." This is the best way to start interpreting the clues you find on plates.
Look at the back of the plate for the maker's mark. The mark may be anything from a small, hand-written symbol, to a kite shape, to an image of royal arms. It may also contain numbers or codes, which were used by companies such as Wedgwood. Your reference materials will help you find the date of production and identify the manufacturer.
On the back of the plate, also look for the name or number of the pattern. If you only find a number, resource books can lead you to the pattern name.
Compare your plate to illustrations in books and on Web sites, if there's not a pattern clue. You also can get help from an expert. Many appraisers have in-depth knowledge of antiques and their manufacturers, as do owners of antique stores.
Send a photo of your plate to a company that replaces discontinued china. The staff will help you track down the manufacturer and the pattern.