What is stated in the autograph by whom, when, where, why and how this could all come under the general heading of content. A President's letters will usually be more valuable if dated while in office, other factors being equal. A President's political letter will be worth more than a social one. A general's war dated letter will fetch more than one written in peacetime, other factors again being equal. This bears repeating because the general's lengthy critique of strategy employed in a battle twenty years earlier will be higher in price than the same general's letter to his wife of war date merely asking how things are at home.
Many people are under the false impression that old paper is ready to disintegrate at any moment.
Actually, pristine American papers of the 18th and even 17th centuries are normal. Old paper was of excellent quality, much better, in fact, than that used today. Soon the beginning collector will be able to put these terms into perspective as they relate to value. An Autograph Letter Signed by any particular person is the most valuable form of his autograph but again we must add other factors being equal. A routine ALS will be surpassed by an LS with good content, or even a DS if it were, say, an order written on a battlefield or a significant appointment.