Another result of the expensiveness of writing material was the practice of erasing whole works in order that the vellum might be used over again. This erasing was done with a knife or pumice stone and when resurfaced by rubbing the vellum could be readily used a second time. A manuscript thus treated is called a palimpsest. The pious monks of the middle ages, naturally believing that the lives of the saints and other religious works were of more importance than the works of Pagan orators, philosophers, and historians, or even than old copies of the Bible which had been superseded by newer and better decorated ones, made extensive use of old manuscripts in this way. Fortunately, however, it is possible by careful treatment to restore the original writing at least sufficiently to make it possible to decipher it. In this way a considerable number of extremely valuable texts which would otherwise have been entirely lost have been recovered from palimpsests. The reference just made to decoration reminds us that the makers of manuscripts, particularly during the middle ages, took enormous pride in their work and were as anxious to produce sumptuous books as the most ambitious publisher of to-day and were often far more successful. The scribe who was to make a fine manuscript chose his vellum with great care. He laid out his work with compass and ruler with the utmost precision. He was careful that his ink and his pigments should be of the most brilliant color and the finest quality. He looked well to the care of his pen and inscribed each letter with the patient care of the most skillful engrosser of to-day. The development of the sentence and paragraph had brought the use of letters of larger sizes to mark these divisions. These, especially the paragraph initials, afforded an endless field for his ingenuity and the exercise of his artistic ability. A great initial letter might be made in any fanciful shape of which he could think. It might become a part of a beautifully executed miniature. It might be surrounded by a mass of gorgeous ornamentation extending to the bottom or the other margin of the page and enriched by everything beautiful or grotesque of which the writer could think. All this ornamentation was often executed in gold and colors and was one of the chief methods of artistic expression of the middle ages.