It would not be possible to say anything about or do anything to it which would not make it more so."[11] Natural ultramarine is the most difficult pigment to grind by hand, and for all except the highest quality of mineral, sheer grinding and washing produces only a pale grayish blue powder.[12][13] At the beginning of the 13th century, an improved method came into use, described by Cennino Cennini in the 15th century. This process consisted of mixing the ground material with melted wax, resins, and oils, wrapping the resulting mass in a cloth, and then kneading it in a dilute lye solution.