You can in any classes planar armour from fear / hate (armour only, NOT shields or weapons), to the classes Guild Master in the area's around the library in Knowledge. You get some xp (majorly nerfed from when it was opened) and radon gems, peridots, raw diamonds, diamonds or blue diamonds. You can turn in any classes armour, jsut be sure to turn it into a GM for that class, which you can find our easily enough by trying to buy / inspect them and they say "Go away you are a member of the guild."