A guy I met on a cruise was annealing his washers by heating red hot then dropping in water. I kept my "knowledge" to myself about slow cooling, etc. When I got home I went to the trusty old Google and found conflicting references about cold water or not. Based on some experiments with copper wire in my shop I could not tell the difference. One advantage to dropping it into cold water is the oxide scale comes off leaving it clean. I made some straps out of 1/2" type M rigid copper plumbing pipe. As it came from Home Depot it was almost as hard as steel. After annealing it was more like Play-Doh. Aint science cool?!