In the "Waves of Madness" world event you can get a "Vial of abyssal water" that adds a glow effect to your weapon. Like most special items in Rift the item description is less than helpfull and they forgot to mention that it's limited to 24 hours.
Are there any way of obtaining a permanent weapon glow effect in Rift?
Update: In later world events, at the moment "Planar Menace", it is possible to buy epic quality item Endless Overgrowth Oil that is bound to account and have infinite charges, that give a 24 hour weapon glow effect. That is 24 hours game time, so in practice it will last for several days or weeks. And when it runs out it can be renewed infinitely for all your alts on that account. That is good enough for me ^^