As a kid working a summer job in a Ford dealership body shop, mid 60's; I watched an old school body man remove hail damage from a rail car load of Mustangs,( Back then, the cars were exposed on the train cars.) using a torch & an ice cube wrapped in a rag. I can't remember if the dent was "circled" by the torch, and the ice applied to the dent, or vice-versa, However done, the dent would pop up, and quickly be stroked with a coarse body file. I remember this as an insurance job, and the shop was chosen because they still knew how to work with body solder, or lead. No plastic filler was allowed. Apparently so the cars could be sold as "new".