The name Crown Ducal originated in 1916. It was used by A.G. Richardson and Co., Ltd., of Tunstall and Cobridge, England, on some pieces of their porcelain. While collectors are drawn to many of the Crown Ducal patterns, some of the label's most famous and valuable motifs are the 1930s, Art Deco-inspired designs of Charlotte Rhead. Knowing which Crown Ducal pattern you own is a matter of doing some research into the maker's extensive design catalogue.
Check your piece for a pattern number. Look at the underside of your china and see if a pattern identification number is stamped there. Use that number to find the pattern name with which it corresponds. The website "Crown Ducal by Charlotte Rhead" shows the numbers and pattern names associated with Crown Ducal's most famous designer.
Look through china collectors' guidebooks. Take a trip to your library or book store and look at the illustrations in books about collectible china. See if your pattern matches any of those shown. There are books devoted solely to the work of Rhead, including "Collecting Rhead Pottery" by Bernard Bumpus and "Clarice Cliff and Her Contemporaries: Susie Cooper, Keith Murphy, Charlotte Rhead and the Carlton Ware Designers" by Helen Cunningham. You can also find general china guides that include sections on Crown Ducal. You may have to go through several books to see multiple examples of Crown Ducal patterns. Examples of books that mention the manufacturer are "English Transferware: Popular 20th Century Patterns" by Joe Keller and Mark Gibbs and "Collectible Cups & Saucers" by Jim Harran and Susan Harran.
Use the service of a china and glass replacement company. China and glass replacement services deal with and have knowledge of many makers and patterns. The company Replacements Ltd. offers a free pattern identification service. Send them pictures of the front and back of your china via email, fax or regular mail, and they will research the pattern. Also, the company's website features many pictures of china patterns. Do a search for Crown Ducal and compare your piece to what you find online.
Compare your piece to others in the marketplace. An effective method for finding the name of your pattern is by comparing it to others that are for sale and have been identified. Because of its large and ever-changing inventory, the auction site eBay is a good resource for this identification method. Hunt for the key words "Crown Ducal" and look at the pictures. Often, you will find an exact match for your dish. Look in both the ongoing and completed auctions. Besides giving a name to your pattern, this research method lets you know what people are willing to pay for pieces comparable to those you own.