You can determine the value of old dishes whether you are having a garage sale and wondering what you should keep or whether you are contemplating buying an old dish at a flea market. Sometimes it's as simple as examining the back of a plate for a manufacturer's mark, and other times you might have to do a little digging, but you should be able to find an approximate value of your plate or dish.
Examine the back of the plate in question carefully, using a magnifying tool if necessary. Dishes usually have a "back stamp" on the back which identifies the name of the manufacturer. This same marking may reveal the name of the city or the country where the plate was made, and some even reveal a pattern name or the date when it was produced.
Do an Internet search to determine an appoximate value. Dishes often sell online for 50 percent of the china replacement list price. Many of the china replacement websites show photos of items to help you correctly identify the pattern and year of the dish.
Do a Google or Yahoo search entering whatever information you have about the dish, according to the markings on the back of it--if you are unable to find your pattern with a china replacement company. Review all the websites of online antique dealers and other plates by the same manufacturer. You can also get an appraisal online.
Make a trip to your local bookstore, library, or browse online collectible encyclopedias such as "Art & Collectibiles" to try and locate patterns that are difficult to find otherwise. Libraries usually have reference books which may help you identify your pattern.
Take a photo of both the front and back of your plate and email it to some collectible plate websites or antique dishes websites to inquire whether they might be able to identify your plate.