Figure 12 Mug, Staffordshire or Yorkshire, ca. 1790–1810. China glaze. H. 6ž¿¢". Polychrome-painted China glaze mugs are much less common than blue-painted ones. The introduction date for underglaze-painted colors has not been documented. One reason that polychrome pieces may be less common is that blue-painted patterns began twenty years before the polychrome-painted patterns were introduced.