from the cliffs of Afghanistan's Bamiyan Valley, "using walnut and poppy seed oils." Pliny mentions some painted ceilings in his day in the town of Ardea, which had been made prior to the foundation of Rome. He expressed great surprise and admiration at their freshness, after the lapse of so many centuries. In the 13th century, oil was used to detail tempera paintings. In the 14th century, Cennino Cennini described a painting technique utilizing tempera painting covered by light layers of oil. The slow-drying properties of organic oils were commonly known to early European painters. However, the difficulty in acquiring and working the materials meant that they were rarely used (and indeed the slow drying was seen as a disadvantage). Paint was made with the yolk of eggs and therefore, the substance would harden and adhere to the surface it was applied to. Pigment was made from plants, sand, and different soils. Most paints used either oil or water as a base (the diluent, solvent or vehicle for the pigment). The Flemish-trained or influenced Antonello da Messina, who Vasari wrongly credited with the introduction of oil paint to Italy, does seem to have improved the formula by adding litharge, or lead (II) oxide. A still extant example of 17th-century house oil painting is Ham House in Surrey, England, where a primer was used along with several undercoats and an elaborate decorative overcoat; the pigment and oil mixture would have been ground into a paste with a mortar and pestle. The process was done by hand by the painters, which exposed them to lead poisoning, due to the white-lead powder. In 1718, Marshall Smith invented a "Machine or Engine for the Grinding of Colours" in England. It is not known precisely how it operated, but it was a device that increased the efficiency of pigment grinding dramatically. Soon, a company called Emerton and Manby was advertising exceptionally low-priced paints that had been ground with labor-saving technology: By the proper onset of the Industrial Revolution, in the mid-18th century, paint was being ground in steam-powered mills, and an alternative to lead-based pigments had been found in a white derivative of zinc oxide. Interior house painting increasingly became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was also increasingly used as an inexpensive binder. In