When I was dismantling my old glass furnace about 2021 for a re-build (with sledge hammer and crowbar) I found a 4" spiral ardor nail sitting in the bottom, surrounded by a large region of amber glass. Occasionally over the years I was getting amber wisps in some of my glass items, now I know why. Who knows how many years that nail sat down there in the bottom of the furnace. Long enough to create quite the plume of amber.