Rookwood Pottery Co. is known for the artistry, style and high standards with which its products were made. It was founded in 1880 by Marie Longworth Nichols and finally closed down production in 1967. The pottery produced has been highly desired by private collectors and museums and--depending on the artist--can be fairly expensive. Learning how to date this pottery is a fairly simple process as long as you can read the potter's mark stamped on the bottom.
Find the potter's mark on the bottom of the object. It is a backwards R with a P.
Count the number of flames crowning the RP logo. From 1886 to 1900, a new flame was added until there were a total of 14 flames over the RP in 1900. For instance, a vase made in 1890 would have four flames.
See if there are Roman numerals under the Rookwood logo that is crowned by 14 flames. These Roman numerals were used to date the pottery from 1901 until 1967. For example a VI under the RP logo indicates the piece was made in 1906.