Often a clear or light greenish glaze used on redware or pearlware vessels; sometimes speckled with dark unmelted lead crystals.
A clear glaze with lead as one of the components. Lead easily leaches [ moves] from the glaze into liquids, especially hot liquids. Lead glaze is poisonous, therefore, not a good choise for cups or anything that is intended to contain food. During the middle ages and before, lead was used to join ceramic pipes for fresh water supplies to villages. History of the middle ages reports crossroad signs warning travelers that residents of the next city were all crazy with lead poisoning and to enter at their own risk. WOW
The most commonly encountered English glaze from the 18th and 19th centuries. Pots were dipped into the clear liquid containing silica and lead oxides before firing. The firing process was such that leaching of the lead when in use, even with acidic foods, was not a problem. The potters working with this mixture, however, were in grave danger.