I thought you were suppose to uh "craft" them, as in Create them.

You create them by going to BoBo The Upgrading Specialist,(near weapon/armor npc in Flaris), and then click on Create Jewels option
-> and put in a weapon level 60+
-> upgrading a weapon increases success rate and # of gems.
-> +5 and higher = 100% success rate of creating a gem

For more information, you can log on to flyff-wiki (dot) gpotato (dot) com. (flyff-wiki.gpotato.com)