em27

Hi, I've started using ecosoya advanced soy to make 8oz tin candles. The candles look good when they have cooled, the problem is that when they burn for about an hour air bubbles come around the wick...then a crack begins to form (see attached photo) which turns into a big cavity around the wick. I've tried all different pour temperatures, I tried pouring cool, as low as 110 degrees and hot as 160 degees, and many temperatures in between and the problem still persists (although crack is lesser at lower temps). I've tried pouring slowly, tilting container as I pour, covering candles to slow cooling etc. The air temperature is a nice 70 degrees here in Australia. I'm using htp wick. I tried doing two pours poking relief holes, this did solve the problem with crack but then air bubbles where coming up from where I had poked the relief holes. I'm not sure you are supposed to do relief holes with ecosoya advanced? Has anyone else had this problem and what did you do to solve it? Please help, I've run out of testing ideas and this is driving me crazy!!