See the discussion in Deutsch, Messages from the Past, p. 163, no. 199. I am indebted to him for photographs of the two bullae and for two drawings made with access to the original bullae. In his drawing of the new Hezekiah bulla, he has seen some detail I do not have on my own drawing, which was made from poor photographs. Hence I have substituted his drawing for mine. His reconstruction of the Avigad bulla is bold but I believe accurate.