Another problem with paper made from wood pulp is that it is porous. Tiny holes in the surface of the paper soak up ink from a printing press, spreading it over a larger area then is intended. To prevent ink creep, a coating of aluminum sulfate and rosin is applied to some paper to seal the holes. This process, called sizing by feeling the surface of a newspaper and this page. Aluminum sulfate was chosen for the treatment because it is color and cheap. Because paper without sizing does not crumble, aluminum sulfate must be responsible for the slow decay. but how?