Why do my soy pillars crack after they have been lit for a while around the top and they turn brittle

After candles cure and they are lit, they crack and turn brittle after being lit. How do I prevent this.


cracking Pillars

I had the same problem with pillars cracking & for me it turned out to be the wax I was using. I switched to Ecosoya & that problem was gone. Now , I am trying to get my wicking right but I'm not clear on how a soy candle should burn. Should it consume itself or leave a thin wall? I'm new to this forum so hopefully I can get the help I need here.