They need to cool REALLY REALLY slowly...like I poured mine, wrapped the molds in folded wash cloths, and stuck them in a pre-heated oven (turned off) to cool. I poured at about 4:30 in the afternoon, and at 11:00 that night the molds were still too hot to touch, even though the oven was cold by then. At that point they WERE cool enough though, to remove the wick sustaining bar which I had been told would increase chances of cracking if it were left in.

I don't poke relief holes in mine and don't do repours. Never had a problem yet, as long as they cool super super slow.

HTH
Carol