I have a question for all of you experienced blacksmiths, my brother has been experimenting with forging using a firepit and bricks as a makeshift forge. He asked me if i would like to come out and help make a knife with him out of a railroad spike. Long story short i got hooked on blacksmithing. Anyway's we have recently required a nice metal tank and were thinking about making it into a better forge than the fire pit that we have been working out of. We are thinking of cutting the top half of the tank off and using the bottom half as our new forge. My question is to prevent the coal from heating through the metal at its high temps, would lining the sides using wood ash as a refractory be sufficient enough to run a safe forge to make knives in? Or do i need to coat it in something else or nothing at all? Hope that makes sense and thanks!