Hardening

You rub your hands along the length of the object, intoning the spell. A warm red glow emits from your hands, strengthening the object.

(Spell Compendium, p. 109)
Originally posted on D&D tools

Transmutation

Level: Sorcerer/Wizard 6, Artifice 7
Components: V, S
Casting time: 1 action
Range: Touch
Target: One item of a volume no greater than 10 cu. ft./level (see text)
Duration: Permanent
Saving Throw: None
Spell Resistance: Yes (object)

This spell increases the hardness of materials. Paper becomes harder to tear, glass becomes harder to break, wood becomes more resilient, and so on. For every two caster levels, add 1 point of hardness to the material targeted by the spell. This hardness increase improves only the material’s resistance to damage. Nothing else is modified by the improvement. For example, a longsword (treat steel as iron, base hardness 10) affected by a hardening spell cast by a 12th-level caster would have hardness 16 for the purpose of ignoring damage caused by someone making a sunder attack. The sword’s hit points, attack and damage modifiers, and other factors are not affected. A hardening spell does not in any way affect a substance’s resistance to other forms of transformation. Ice still melts, paper and wood still burn, rock still becomes transmutable to mud with the proper spell, and so on.

This spell affects up to 10 cubic feet of material per level of the caster. If cast upon a metal or mineral, the spell affects only 1 cubic foot per level.

Material Component: An ointment made with 50 gp of diamond dust per 10 cubic feet of material.