My HS ceramics class recently did a project based on Bernard Palissy's rustic platters. The students rolled out slabs of clay and then laid them in platters (picked up from the thrift store) to give them form. One student did a beautiful ocean scene on her platter. She used red clay for the actual platter and then added pieces cut out of white clay on top. The problem is, as the platter dried, the red clay started to crack. I originally told her to mend it with some soft clay. The platter cracked again. The next time we mended it with a vinegar slip. The platter continued to crack. The red clay we have does tend to be a bit more difficult to work with in general. Is there any way to save the platter at this point? Right now it's in a leatherhard state. Any advice on this matter would be greatly appreciated.