Thanks to all of you who contibuted to this thread. Here is what I
Vulcanised Yellow Label rubber at 345 F (308 F is recomended)
Quenched the mold in cold water.
Heated the wax 15 F hotter than usual.
Results: ring shrunk from finished model to finished 14K ring by
about 7%. Good enough! (10% would have been my target)
BTW Castraldo products are very consistent. The wax made from a
white label mold, vulcanised at 308 F and air cooled was only 0.1 mm
wider than the mold I pushed to get maximum shrinkage. The model was
6.9 mm wide, the waxes 6.8 and 6.7, the casting 6.65 and the
finished ring 6.5.