I'm a GM Tinker and put on my Tinkering talisman with 23 exceptional bonus and still only had like a 28% chance to craft an exceptional jewel. So I burnt threw a few RARE gems and made 21 whole piece of crap jewels. One of the exceptional ones had a whole 2 mods on it, not sure what they were now since I threw the bag of crap in the public dump. What a waste...