There is also an ancient Crystal of Light that Matoya owns from a past Umbral Era (the one Krile used to track down Y'shtola in the Lifestream), which is particularly potent (due to apparently being more 'pure') - unlike our own Crystals, this one seems to be completely physical rather than more aetheric like the ones possessed by the Warrior of Light, which probably explains it's purity.

Also, whatever became of that synthetic Crystal of Darkness manufactured by the Students of Baldesion that Minfilia made such a big deal about explaining just prior to Operation Archon? (the one she planned to use to free Thancred from Lahabrea's thralldom? - Lahabrea was directly driven out of Thancred's body in the Lifestream by Hydaelyn Herself so it made that whole thing nothing more than a red herring at best). I presume given what it was planned to be used for it probably is quite potent aether wise.