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Ricardia Ware produced by Richards Tiles in Stoke-on-Trent The glaze is, or is very like, one of the Richards Tiles' pre-war WM (wall mottle) glaze series. Those glazes contained oxides of lead which gave them certain flow and appearance characteristics. The use of lead oxides in glazes was banned after1947 because of their causation of lead poisoning of operatives. Lead bisilicate was substituted but it was not possible to get the same results.