Types
Look underneath pottery and porcelain for an identification mark. Anything that is marked "England" or "English Bone China" is not antique, but manufactured in modern times, after the 1900s. Porcelain marked with the word "Royal" was made after 1850.
Significance
Research marks found on pottery and porcelain in appropriate guidebooks. Certain symbols used on porcelain and pottery can be found listed next to company names within guidebooks. These tell the history of the company and may also date the piece of piece in question.
Identification
Examine the coloring of the mark. Anything other than blue would be a piece made after 1850. Look for design abbreviations, such as "RD" or "Ltd" (or the whole word "Limited"). These markings were used on pottery and porcelain after 1885. Pieces that are marked "Trademark" were manufactured after 1862.
Considerations
Obtain an appraisal from a professional antique dealer familiar with antique porcelain and pottery. Get a written estimate if possible.