Using low heat or hot bath is the quick fix but is risky because the core acts as a heat sink. The densities in the core contract with heat and expand when cooled. The coverstock cools down before the core does. The coverstock is at risk of being fractured from the core cooling and expanding. Hope this helps
I would disagree with that statement.
The core heats and cools at different rates, because the heat energy is transferring into the ball at first, but for the heat to dissipate, it has to then radiate from the center outward.
The only common material that expands when cooling, and shrinks when heated on Earth is water. I think you will find that ball materials (including ball plug) will expand with heat, and contract with cold. You are right about those expansion and contraction rates being different across the different densities of ball material, hence the danger for cracking when a ball is exposed to extremes in temperature.