Most churches have been rebuilt, often several times, but medieval palaces and large houses have been lost at a far greater rate, which is also true of their fittings and decoration. In England, churches survive largely intact from every century since the 7th, and in considerable numbers for the later ones—the city of Norwich alone has 40 medieval churches—but of the dozens of royal palaces none survive from earlier than the 11th century, and only a handful of remnants from the rest of the period. The situation is similar in most of Europe, though the 14th century Palais des Papes in Avignon survives largely intact. Many of the longest running scholarly disputes over the date and origin of individual works relate to secular pieces, because they are so much rarer - the Anglo-Saxon Fuller Brooch was refused by the British Museum as an implausible fake, and small free-standing secular bronze sculptures are so rare that the date, origin and even authenticity of both of the two best examples has been argued over for decades. The use of valuable materials is a constant in medieval art; until the end of the period, far more was typically spent on buying them than on paying the artists, even if these were not monks performing their duties. Gold was used for objects for churches and palaces, personal jewellery and the fittings of clothes, and—fixed to the back of glass tesserae—as a solid background for mosaics, or applied as gold leaf to miniatures in manuscripts and panel paintings. Many objects using precious metals were made in the knowledge that their bullion value might be realized at a future point—only near the end of the period could money be invested other than in real estate, except at great risk or by committing usury. The even more expensive pigment ultramarine, made from ground lapis lazuli obtainable only from Afghanistan, was used lavishly in the Gothic period, more often for the traditional blue outer mantle of the Virgin Mary than for skies. Ivory, often painted, was an important material until the very end of the period, well illustrating the shift in luxury art to secular works; at the beginning of the period most uses were shifting from consular diptychs to religious objects such as book-covers, reliquaries and croziers, but in the Gothic period secular mirror-cases, caskets and decorated combs become common among the well-off. As thin ivory panels carved in relief could rarely be recycled for another work, the number of survivals is relatively high—the same is true of manuscript pages, although these were often re-cycled by scraping, whereupon they become palimpsests.