From around 70 AD colourless glass becomes the predominant material for fine wares, and the cheaper glasses move towards pale shades of blue, green, and yellow.[1] Debate continues whether this change in fashion indicates a change in attitude that placed glass as individual material of merit no longer required to imitate precious stones, ceramics, or metal,[2] or whether the shift to colourless glass indicated an attempt to mimic highly prized rock crystal.[3] Pliny's Natural History states that "the most highly valued glass is colourless and transparent, as closely as possible resembling rock crystal" (36, 192), which is thought to support this last position, as is evidence for the persistence of casting as a production technique, which produced the thickly walled vessels necessary to take the pressure of extensive cutting and polishing associated with crystal working.[1]