Antique porcelain was made up until 1910. Antique porcelain can be anything from cups, saucers, plates and decorative items (both plain and hand-painted) to decorative wares. Many collectors and antique dealers identify antique porcelain by looking at various types of markings underneath the porcelain itself. Some pieces are marked with a company name. Others are left unmarked and may be identifiable by pattern only, or by numerical symbols or other codes.
Turn your piece of porcelain carefully to the underside, and look for a marking. Porcelain pieces that say "English Bone China" or "Bone China" are not considered antique, but were made after 1891, with the majority of modern pieces manufactured in the 20th century.
Write down any marks to research in guidebooks about antique porcelain. Well-known porcelain companies such as Wedgwood, Meissen, Doulton, and others used symbols. Look up markings in a current price guide-book, to get an exact date of production, and value.
Learn about the various antique porcelain manufacturers, and study about the kind of antique porcelain that interests you. The more you know about a specific company and its history, the easier it is to identify marks and characteristics of the porcelain in your collection.
Look at the coloring of the mark. A printed or stamped-on mark in colors other than blue indicates pieces that were made after 1850. See if the word "Royal" is stamped before the company name. Pieces with the word royal were also made after 1850.
Check registration marks. Design registration marks are abbreviated as "Rd," with numerals following, and were used on porcelain between 1842 and 1884. Find the markings that have the word "Limited," or "Ltd." These markings stand for limited liability companies, and were generally used on pieces dating from 1885 on. Look for the words "Trade Mark." This usually dates porcelain from 1862 on, for that is when the Trade Mark Act became law.
Look for month codes on antique porcelain. These were capitalized letters that stood for various months within a year when the factory produced the porcelain. Check near the name of the company on porcelain for any capital letters that might indicate the month or year when the piece was made.
Bring your porcelain to a professional antique dealer. They are more familiar with antique markings on old porcelain, and sometimes will give an estimate of date and value, or may offer professional appraisal services. Search online auction sites, and websites with pictures of porcelain marks. Sometimes websites will have detailed information, including history and dates next to the mark.