Sith crystal

Though red crystals were ordinarily unsuitable for use in lightsabers, the Sith discovered that by energizing red crystals with the dark side of the Force the crystal would glow in harmonic vibration. These "Sith" crystals could in fact produce a stronger lightsaber blade than regular crystals which had the rare potential to "break the blade" of standard lightsabers by overloading the energy matrix and instantly burning out the other 'saber. Though this happened extremely rarely, it was a known and frightening possibility in combat.