Painted Hide Cave Paintings and any other method of putting symbolic ideas onto a flat surface. A little research goes a long way. Also important is the 'version' of the language, like old english or modern english, if anything else it adds flavor to the tome. This will have to be deciphered to even begin to read the tome. A page missing here, a blood stain there could all lead to the misunderstanding of the work.
Condition ranges from immaculant to abysmal.
An abysmal tome could be more than half-burned, worm eaten, acid burned, or what ever. Also common to these types of books are marginal notes, extra pages of notes and such stuffed in the books, these can either raise or lower the diff of a tome, depending on wether they help or mislead the reader. Gilt, stones, leathers, and other precious substances went into decorating these tomes. On the inside, hand illuminated script, color plates, and marginal notes all add to the flavor of the book. Now, the system itself.