They were originally formed as radial extensions from the outer surface of the muffle wall to act as supports bearing against the inner surface of the firing chamber. In the space bridged by these supports the fire was able to circulate around the muffle. Props are generally columnar in form displaying the irregularities generic in a roughly hand made object. They commonly take the form of a truncated cone, the broad end springing from the muffle Figure 4a . Some examples splay also towards the extremity.
Bars occupy the same position and serve the same function differing only in shape.
They are of sub-rectangular prism form. In use the greater dimension had a vertical alignment, the bars being arranged in the manner of vertical ribs around the outside of the muffle Figure 4b . The teardrop variation of the bar is described above. Ridges are in the form of triangular prisms lying on one face similar to a pitched roof Figure 4f . Props, bars and ridges are commonly made from the same materials as the muffle and constructed as integral parts of it.