When brown color changes and dark spots appear on old documents and the pages of old books, these blemishes are referred to as “foxing”. The term “foxing” is based upon the term “ferrous oxide” borrowing the letter “f” in “ferrous” and the letters “ox” in “oxide”. Foxing occurs when paper becomes exposed to humidity and as part of the oxidation process when iron, copper, or other metallic substances within the pulp from which the paper was made are exposed to oxygen to form iron oxide which is rust