There are many ways to identify the period of manufacture of Wedgwood china. For the casual collector or enthusiast, the simplest means of telling when a particular piece of Wedgwood china was produced is by the configuration of the stamp, or maker's mark, located on the bottom of the piece.
Since the company's founding by Josiah Wedgwood in 1756, the stamp, or maker's mark, found on the underside of nearly every piece of Wedgwood china ever produced, has changed many times. In most cases, certain marks were used for a limited time, making age identification fairly simple.
The earliest known mark, possibly used by Mr Wedgwood himself, appears to have been engraved by hand, or embossed in the unfired clay with a hand-made stamp. The website collectingwedgwood.com, while a hobby site, is thoroughly researched and offers images and dates of use of the different stamps and marks used over the years.
One mark, however, consisting of the word WEDGWOOD in all capital letters, either impressed in the raw clay or printed on a fired but unglazed piece, has been in use on the Queen's Ware line since 1769. As a result, the only way to attempt to identify the age of Queen's Ware is to research the various painted decoration patterns, which have been added to and discontinued from the line over the years. A good place to start would be the Archives of the Wedgwood Museum at www.wedgwoodmuseum.org.uk/archives.