Design dates are best determined from the Crown Ducal pattern number. Spare cup and saucer by: Vintage crown ducal orange tree small plates circle and hexagonal Art Deco unusu. Comes from a smoke-free home. In the floral 'Wilmslow' pattern with hand coloured underglaze. However, if the premise that named patterns had their own backstamp style turns out to be true, then if those patterns had extended production runs then the date ranges might have to be reconsidered. Types and are specific to the Ivy pattern, another single print colour design that was particularly popular in the USA.
Type is found on a large number of patterns.
Crown Ducal Pottery Mark - Florentine Picardy
Posted by Ian Newton at Pattern number is Louis. Sugar lid has tiny nick inside lid. Small pinprick mark in the glaze on foot. You can get a fascinating into Charlotte Rhead's work and the patterns of Crown Ducal here: