Butane Test results from another forum.
Best to Worst (note there are two Xikars, UK and USA, two Fasfils, UK and Korea, and two Purtanes, the original, and 9X)
Ultra Pure had 0.001g of residue
Ultra Pure, England, 300ml can, reads on the bottom "DOM 27.09.13 06:58"
Special Blue 7X had...