Unbreakable (Ex)
Source: Ultimate Magic, p. 48
As long as it has at least 1 point in its arcane pool, a black blade is immune to the broken condition. If broken, the black blade is unconscious and powerless until repaired. If destroyed, the black blade can be reforged 1 week later through a special ritual that costs 200 gp per magus level. The ritual takes 24 hours to complete.