According to LoveToKnow, finding the value of old dishes involves knowing some information about the dishes including the manufacturer, rarity, provenance, condition, age, supply and demand, type of dish and pattern. Sometimes knowing only a few of these details is enough to determine the value of the dish.
LoveToKnow says that some old dishes have identification markings on the reverse side. This gives owners a head start in determining the value of the dish. Often times, the reverse side of the dish clearly marks the manufacturer's name. Others might have identifying marks that older manufacturers previously used when marking dishes. Sometimes the name of the pattern used on the dish is also on the reverse side. If the pattern name is not on the back, companies such as Replacements Ltd. offer a completely free database of images to help determine the style of the pattern.
For unmarked dishes, the owner has to determine if the dish is earthenware or porcelain, according to LoveToKnow. Holding the dish up to a 100-watt light bulb helps people determine the type of dish. If the light shines through, it is porcelain. If no light shines through, the dish is most likely earthenware.