Though they have been used since the 12th century, glazed flat tiles really spread in the 14th century. They colonized the bell towers and roofs of many palaces and places of worship throughout France. Glazed tiles are glazed with a layer of glass entirely made of sand and lead, while enameled glazed tiles consist of a layer of glass enriched with tin. The addition of mineral salts to these mixtures of sand, lead, and tin allows obtaining different shades (yellow, orange, green, red, brown) that, depending on the arrangement of the tiles, result in the creation of patterns.