Check out this video to learn scoring techniques of joining two pieces of stiff leather-hard clay.
Following are some steps you will see demonstrated
1. Mark the area needed to be scored
2. Score all areas that will be touching with a needle tool in a cross-hatched pattern.
3. Wet the scored area with a brush(50 part water + 50 part cooking vinegar works really good too)
4. Scratched all the area again to make slip on all the joining area.
5. Attached the pieces, taking care not to trap any air in the joints, and put firm pressure, pushing both pieces against one another.
6. use a clay coil to reinforce the joint
7. smooth out the coil to the rest of the pieces.
8. Wrap the whole project in plastic to equalize the moisture of the whole project. More extreme and complicated parts, with thick and thin parts need to be left in the plastic longer to dry gradually and slowly. Depending on the complexity of the project, leave the project wrapped in plastic between one day to a week.
9. After equalizing the moisture of the clay, take it out of the plastic and let it completely dry out before it can be bisqued fired.
* Clay is best attached when it is in the leather-hard stage, when the clay is stiff but still a little flexible. If the clay has already lost it's sheen, then, it is too dry to get a successful attachment.