Service plates were first made in the 1930s in different sizes. They were made with wide rims and didn't belong to any particluar line of dinnerware.
A special 10" service plate was created in October of 1938 for the Golden Gate International Exposition. It was listed in the modeling log as a plain Georgian 8" plate (in trade size) and was modeled by Al Kraft. The 10" service plate was put into production On November 12, 1938. A plain ashtray was also created for the Expo in November of 1938. The colorfully decorated Exposition plates can be found with 1939 and 1940 dates. A special circular backstamp was also made for the plate which can be found either with or without the standard HLC marking.
The 10" plate was also used for the New York World's Fair. Like the Golden Gate plates, the Fair plates come decorated with 1939 and 1940 dates. Many of the New York World's Fair plates used blanks already marked with the Exposition backstamp. The Expo marks had to be blotted out in gold.
There was also an 11" service plate. Both the 10" and the 11" sizes were decorated with colored rims, center floral decals, and elaborate gold stampings. These are almost always marked with a 22 Carat Gold stamp in addition to the regular HLC mark. Like the NYWF plates, floral service plates can be found with blotted out Expo markings.
A collector may want to find more pieces to go with service plates to build a set. Unfortunately, most the service plate treatments were not used on other shapes. There are a few exceptions, namely the two treatments used on the Brittany cups and saucers which can be seen at the bottom of this page.