In Ultima V, jeweled weapons could be obtained from Thrud in Windemere, but only after joining the Oppression. Thrud demanded the password of the Resistance in exchange for them. Despite the high price paid for the weapons, these supposedly fabulous swords turned out to completely useless in combat.
Who can explain the ways of Evil? Why would anyone for Evil's cause or any other, forge a shining sword that can do no damage and a suit of fine plate armour transparent to a foe's blade? Seek the answer if thou wilst, but remember along thy way to beware of any highly touted gifts to thee by Thrud of Windemere, Servant of Blackthorn.