Getting right to it this morning, I made some modifications to the lower firing chamber's mold. Knowing now that I have to get the mold out of the clay as soon as possible to prevent the clay from splitting again, I cut the mold into 3 parts. By shaping the centre part like a wedge, it should be easy to pull it out of the clay, allowing the other two parts of the mold to come out easily.
I lined the two sides of the centre section with clear packing tape to allow it to slide out easily.
Once I'd done that, I proceeded to lay the clay out on the mold. It gets a lot easier and faster the second time around
I'll leave the clay on the mold for about 36 hours, just enough for it to dry to the consistancy of leather, before I remove the mold.