In Holland, the manufacture of tin glazed ware became so closely associated with the town of Delft that the ware became known in England as Delftware though the process was firmly established in England before it was in Delft. In its making, a body of porous, buff-colored clay, was fired before it received its glaze of powdered sand (silicate of potash) and oxides of lead and tin in an aqueous suspension. When the glaze was dry, the surface could be painted with various metal oxides, which when fired produced the color—cobalt for blue; manganese for purple or black; copper for green; iron for brick-red and so-on.
Once the design was completed the piece was given a second firing at a higher temperature to finish the job. c1628-1770