The fifteenth-century wares that initiated maiolica as an art form were the product of an evolution in which medieval lead-glazed earthenwares were improved by the addition of tin oxides under the influence of Islamic wares imported through Sicily. Such archaic wares are sometimes called "proto-maiolica". During the later fourteenth century, the limited palette of colours for earthenware decorated with coloured lead glazes (no added tin oxide) was expanded from the traditional manganese purple and copper green to include cobalt blue, antimony yellow and iron-oxide orange. "Sgraffito" wares were also produced, in which the white tin-oxide glaze was scratched through to produce a design from the revealed body of the ware. Scrap sgraffito ware excavated from kilns in Bacchereto, Montelupo and Florence show that such wares were produced more widely than at Perugia and Città di Castello, the places to which they have been traditionally attributed.