You can weaken or strengthen the substance of an object or structure. You can affect both mundane and magical inanimate material. Weakening an object's substance decreases its hardness and hit points, and strengthening it increases its hardness and hit points. You can increase or decrease an object's hardness by up to 5 from its original hardness. When hardness increases, the object (or portion of an object) gains 3 hit points per inch of thickness for every point of increased hardness. When hardness decreases, the object (or portion of an object) loses 2 hit points per inch of thickness for every point of decreased hardness (to a minimum of 1 hit point per inch of thickness).
You can't decrease the hardness of an object that already has hardness 0.
Working Manipulated Metals
An object or portion thereof whose hardness is decreased or increased is permanently changed. Even hardening adamantine to 25 is possible. You can also harden or weaken a preforged weapon, a suit of armor, or some other finished item.
250 XP for each point by which the object’s hardness is altered.