If you have a gas high temperature kiln, shape or mold the shape you need and apply a salt glaze and fire. If not forget about anything other than high fire ceramics.
Wood, glass, plastic, and even paper in my experience do not do the job. Even unglazed ceramics like bricks are no good.
I have found that discarded ceramic electrical insulators such as you might find outside your utility company can be very good, although they might not have WAF.