Thanks so much for your feedback, it has really, really, helped. I took your advice and lowered the fo% to 6% and retested with a zinc 52. I burned in 2 to 3 hour increments, with one 5 and one 7 hour marathon burn. There was some inital blackening of the glass early on, I wiped it clean and have not cleaned it since then. You can see some blackening continued, but I dont' think it's bad considering I have burned this for a total of 35+ hours. I've mentioned earlier that the blackening in the photo looks worse than it actually is. Any additional feedback on this test would be greatly appreciated! I'm feeling good about this one, I hope it's a winner. (famous last words, huh?) Thank so much. This photo is after a three hour burn, using j223, 6% pear spice, and 16oz mason jar.