1: If you roll a natural 1 it is a critical fail. On a critical fail, roll a 1d20 to see what happens.
1-5 Weapon shatters. 6-10 a large chip flys off the weapon, making it less balanced -1 to attack.
10-15 The weapon cracks, making it much easier to break. The next time you roll a conformation for a critical fail a 1-10 shatters the weapon.
16-18 A small chip flys off the weapon, making it easier to break. A 1 or a 2 using this weapon is a critical fail.