Skillet Molding, and Furnace Failure

I started out last Saturday making the molds and melting metal to pour a square skillet that a friend made a pattern of. The furnace's burn tube failed, which occluded the flame from reaching the chamber. I end up the video showing the new firebrick flame tube interior.

I used some hard and some soft firebrick. I suspect there will be more to this story, as I don't know how long the soft firebrick will last.