Franklin did design the first iron stovefront for fireplaces. He did so using the studies in heat conduction by Count Rumford, aka Sir Benjamin Thompson, born 1753 in Woburn Mass. There are very shallow, tall and elegant looking fireplaces called Rumfords still to be seen in older homes and restorations. We don't hear much about Rumford, he was a loyalist and left with the british in 1776 and gained his title working in Austria. Once again, victory, and history go to the winners. You had fun experimenting, coming to similar results as others.