Taking care of book collections. As far as protecting the pages of books, the most important thing libraries do is provide humidity-controlled environments. Books have lots of enemies and one of the best...
Books have lots of enemies and one of the best things you can do is keep them in their dust jackets and keep the dust jackets in good condition. Most books printed in the last 100 years come with dust jackets. In addition, having the original dust jacket can also make a big difference in the resell value of a book. What I like to do is buy the plastic covers libraries use and put those over the dust jackets. You buy the plastic covers at library supply stores.
As far as protecting the pages of books, the most important thing libraries do is provide humidity-controlled environments. Air conditioning also works to control humidity. Unfortunately, the newer paper is pretty acid-filled and isn't going to last very long anyway. Some of the cheaper paperbacks will start falling apart in a couple of years.
Books also respond poorly to insects and need to be protected. Some types of insects will eat the glue from the bindings, while others will eat the actual paper of the pages. Pets and children are other things that books need protecting from.
As far as writing in books and inscriptions, when I was a kid in school the teacher said, "Never write in the book and never pull down the corners of the pages." Pretty much I've lived that way for my whole life and yet I love to collect books that have inscriptions in the front.
I have a great story about inscriptions. I have a collection of books by a guy from the 1930s. He was editor of Sport Life Magazine and he wrote about prehistoric war ... I call it prehistoric fictions. This guy wrote a book and I bought a copy of the book and it was inscribed by the author and the name was somewhat uncommon, so I was able to look it up on the internet. I found his name and an e-mail address and I wrote to him and asked if this was the guy who owned this book. He said, "Yes I was a little boy and my father was a friend of the author and the author gave me that book." So I made a whole web page about that guy and his book and soon after he dies because he was almost 90 at that time. When he died his son wrote to me and said that his father had been so thrilled to see his book and his story up on the Internet and it never would have happened if somebody hadn't inscribed the book.
