I use left over cooked rice and sometimes I let the rice dry out for several days. When I leave the rice out for too long, they start to dry out and get hard and crusty. Then I rehydrate them to soften them up again so I can wedge them with my paperclay. Could this affect the outcome? Perhaps some moisture still remains within the clumps of rice causing the blow out.
This method of making my hand-formed bowls and cups takes so much longer to make than if it had been thrown on a wheel. The successful end product, however, it worth the effort.