Hi again Patty. Several books tell how to "decode" the registry diamonds; the letters and numbers in the corners of the diamond give the day, month and year the design was registered. One of Geoffrey Godden's handbooks of marks also has a table in the back with all the ceramics registrations from 1842 till 1883, when the diamond was discontinued. Just a matter of figuring out the date and then looking it up to see who registered the design. You can do a lot with the right books!