Using a trick probably learned in elementary school whereby paper is folded in half
and then a shape cut resulting symmetry around one axis without even thinking about it.
In this case, the one pattern was transferred to cardboard and trimmed out with an Xacto
knife resulting in a stiffer piece. Such a piece still has some flex - mat board can be
used to make even stiffer templates. These are positioned on the clay and successive cuts
with a needle tool used to trace the shape and cut through the clay. Occasionally one
might prefer the template be the shape of the opening as opposed to the negative shape.