Flintknapping Heat Treatment
Just some comments on heat treating rock, the furnace itself is surrounded by metal shelves etc., so there is not a problem with accidental combusion. One thing I forgot to mention was that oil from cutting rock does distill out of the furnace so a little thin oil slick has formed on the metal shelf above and below the furnace. I tend to wipe down those areas from time to time. Also as the cutting oil moves around it smells like a burnt crayon so furnaces need to be outside. Prices for controllers, solid state relays and thermocouples have gone down significantly since I built my furnace. So this is not an unreasonable project to do.