The permanency and durability of books is largely a matter of relativity and fortuity. We quote from Mr. E. C. Richardson concerning the factors affecting the survival of books: "The average chance of an individual book for long life depends (1) on the intrinsic durability of its material, or its ability to resist hostile environment, (2) on isolation." He says, further: "The enemies to which books are exposed are various: wind, fire, moisture, mold, human negligence, vandalism, and human use. Some materials are naturally more durable than others. Stone and metal inscriptions survive better than wood or clay, vellum than papyrus or paper. On the other hand, however, if isolated or protected from hostile environment, very fragile material may outlast more substantial. Papyrus has survived in the mounds of Egypt, and unbaked clay tablets in the mounds of Babylonia, while millions of stone and metal inscriptions written thousands of years later have already perished. Here the factor of isolation comes in. Fire and pillage, moth and rust, and the bookworm destroy for the most part without respect of persons.... An unbaked tablet which has survived 5,000 years under rubbish may crumble to dust in five years after it has been dug up and exposed to air. The general law is that value tends to preserve, and it has been remarked that all the oldest codices which have survived in free environment are sumptuous copies. Literary value on the other hand is, on the whole, a factor of destruction for the individual rather than for survival. The better a book is the more it is read, and the more it is read, the faster it wears out. The worthless book on the top shelf outlasts all the rest."[18]
There is a department connected with some of the libraries of this or other countries devoted to the specific mission of repairing dilapidated or time-worn manuscripts or documents which, for one reason or another, it is desirable to preserve. The following is reported to be the method followed at the Wisconsin Historical Library: The first thing done is to place the document between wet newspapers under weight and leave them for several hours. This removes the creases and the dirt. They are then put between wood pulp boards and left for a day and then between blotters to complete the drying process. The next step is to repair the paper. The paper in some of these documents is so old and fragile that rough handling will destroy. Therefore it is strengthened by a sort of transparent cloth on both sides of the paper. With some, letters need to be mended along the edges with parchment paper. To cover holes a piece of paper is glued over the edges and is left larger than the holes until dry. It is then cut down to the proper size, and the edges sandpapered until it is smooth. It is then ready for mounting or filing for a continued lease of existence.