Wedgwood color dating
Certain dates can be commented on with some degree of authority, however if a certain color is requested, that color can be "resurrected" for production use.
There are always exceptions in regard to colour and date concerning Wedgwood Jasper.
From 1886 to 1897 the first 12 characters were re-used. Again from 1898 the letters A to I are re-used but are easy to differentiate as they also have ENGLAND within the Wedgwood marks.
By becoming familiar with the dozen or so main variations of the Wedgwood mark and by knowing when each was in use, a collector can determine an approximate period of production of an object.
A guide to trademarks is listed here and by careful study most collectors can acquire a reasonably sound knowledge.
Unlike the easily copied potters marks used by other manufacturers, for example the crossed swords mark used by Meissen; the Sevres double L mark, or the Chelsea anchor mark.
Early Wedgwood works may be unmarked, but the presence of the correct mark is an indication that the piece is genuine and should allow you to determine its true age.