Jerry unfortunately there was no base answer, rather just 'extremely high temperatures' Most of mine are in a glass cabinet with a few holes, save a few that i don't have room for and am still yet to build a new shelf/cabinet to show them in. I'll have to get some plastics slips to seal them in and put them in a drawer until i get around to it. My suspect one appears to be starting around the stitching, strangely its the best condition one i have, that looks to have been treated very very well, almost unissued condish. Could it be something in a leather treatment that can trigger it off? Also a bit off topic, but i did get around to using that Connollys - LOVE it, it's the bomb!