degenerated over time to a single fringed line. Human record-keeping arguably dates back to the cave painting boom of the upper paleolithic, some 32,000–40,000 years ago. More direct antecedents are the writing systems that developed in the 4th millennium BC. Written record keeping and information sharing practices, along with oral tradition, sustain and transmit information from one group to another. This level of preservation has been supplemented over the last century with the professional practice of preservation and conservation in the cultural heritage community. Oral tradition or oral culture, the transmission of information from one generation to the next without a writing system. Antiquarian practices, including scribal practice, burial practice, the libraries at Pergamum, Alexandria and other ancient archives. Medieval practices, including the scriptorium and relic collection Renaissance and the changing conception of artists and works of art Enlightenment and the Encyclopedists Romantic movement's imperative to preserve Significant events 1933: William Barrow introduces the field of conservation to paper deacidification when he publishes a paper on the acid paper problem. In later studies, Barrow tested paper from American books made between 1900 and 1949, and learned that after forty years the books had lost on average 96 percent of their original strength; after less than ten years, they had already lost 64 percent. Barrow determined that this rapid deterioration was not the direct result of using wood-pulp fibers, since rag papers of this period were also aging rapidly, but rather due to the residual sulfuric acid produced in both rag and wood pulp papers. Earlier papermaking methods left the final product only mildly alkaline or even neutral and such paper has maintained its strength for 300 to 800 years, despite sulfur dioxide and other air pollutants. The manufacturing methods used after 1870, however, employed sulfuric acid for sizing and bleaching the paper, which would eventually lead to yellowing, brittle paper. Barrow's 1933 article on the fragile state of wood pulp paper predicted the life expectancy, or "LE", of this paper was approximately 40–50 years. At that point the paper would begin to show signs of natural decay, and he concluded that research for a new media on which to write and print was needed. 1966: The Flood of the River Arno in Florence, Italy, damaged or destroyed millions of rare books and led to the development of restoration laboratories and new methods in conservation. Instrumental in this process was conservationist