But since the crystals dont break anymore, its easy to lvl one up to 5. Just ask a friend that is about 60 or higher to kill 1 buffround of Doom Knights at dev.castle.
Just so you know, a cheap way to get them, if you wish, is to go to the DE Guild in Oren and start the Enhance Your Weapon" quest. The NPC will give you the color crystal of your choice. You take it to the stage you want by kill monsters that are identified in the quest. This will work for up to, I think, stage 10. Higher levels have to be done through special raid bosses, or else bought from somebody else who has done this. But, I think you don't have to worry about the higher stages until you get to A grade weapons.
One thing I don't know myself, is can the crystals be leveled by a nuker or archer, or is it only practical to try leveling them with a melee toon. Since my "main" mains are Orcs, I've never had to find out if ranged classes can effectively level the crystals.
Nukers can indeed level them but you have to run into range to use the crystal, and this means you are going to get hit before the crystal does it thing and the second nuke lands...
Getting swatted by one mob is not really a big deal, but if you get two or more adds, you are not going to get to use the crystal on at least one and indeed you are in a potentially bad situation as a mage.
A melee is a lot better off (especially a paladin) where if I get two or three things beating on me I can completely ignore them and just finish the job or using the crystal then pick the next one and do the same...
Archers do fine as their defenses are higher than the mage and their archery cannot be interrupted with normal hits.
seal of shillied is the only place to lvl to 10 I think, and mages cant realy level them there... the knights stuns and if stun lands (pretty common) a mage will die.