The door is closed by stacking firebrick up in a double-thick wall. The joints are staggered and occasionally bricks
are placed running front to back to bond the two wall thicknesses together. It is also necessary to bridge some ports
that can be used to observe pyrometric cones to check firing temperature. The bricks, which have been stacked
outside are having loose crud scraped off to avoid risking it falling inside and spattering pieces.