From the time of invention of paper, it has been thought that paper would last very long if the condition of its preservation was kept good. Many pieces of archives of the registry of Japanese provinces are preserved in the Treasure House of Royal Domestic Ministry of Japan, Shoso-in, from 8th century. Paper has been proved to be an excellent recording medium and be durable for many hundred years. However, William James Barrow pointed out about 30 years ago that paper, especially modern machine-made paper produced only 50 years ago caused deterioration. On the basis of his suggestion, studies on the deterioration of paper started in the United States 30 years ago. It was concluded that the principal cause of deterioration of paper is the acid hydrolysis of carbohydrates that is induced by the hydrolysis of alum indispensable to modern paper making.
For longevity of book, many deacidification proceses were tried. Two of them are in practice, the one is diethyl zinc method that is used in the United States Congress Library and the other is methyl magnesium carbonate method in Canadian National Library. The latter is commercially available as Wei T'o method. Superiority of the method is now under discussion.
In Japan, committee of protection of book against acid deterioration was organized in National Diet Library in 1982 and quality of book in the Library was surveyed at first. The degree of deterioration of books and journals increased with the age except the era of appearance of wood fiber-based paper, 1850-1880. This tendency was the same as that of California State University Library. The effect of deacidification treatment was tested using Wei T'o method. After 4 weeks ageing, methyl magnesium carbonate was sprayed on the aged samples. Spraying decreased markedly the rate of ageing of paper.
