Georgian- leads or any frames where the glass can't flex has a risk of cracking but it does give you a slight warning if you listen lol,I've known glass to shatter in summer from the stress it's had put on it from hot WFP in winter. Boffin I once spoke to told me that cleaning in winter with really hot water will stress the glass over time although not to the naked eye even in summer months,I've known a few hot water WC,s said customer told them they had a window just go pop on them ie completely shatter for no reason.