My chanter has 193 skill and failed 7 in a row. 2 attempts one day and 3 then next. I lost diamonds, black sapphires and jacinths. Msg said I lacked the skills.
Beware, this isn't automatic. With a JC of 250, 210 INT, and Geerlock Gem Cutter, I still failed in my first attempt to make this item. The other mounted Gems gave me no problem. Probably just bad luck. :-(