The Anatomy of  Photograph 

Card Stock - The photographic paper of the 19th century was so thin and fragile, it required mounting on a more sturdy card stock.  Early stock (1860s) was frequently cut from general purpose press paper board.  (This is the main reason most early cards are square corners).  However, much of this card stock contributed to the deteriorateion of many pictures.  Impurities in the stock would leech through the photograph and stain the picture  

Much of the materials used in the 19th century were highly organic.  Not only did the paper come from wood pulp, but the dominate picture binding was developed from egg whites (albumen).  The binding was the material that coated the paper and held the silver nitrite solution