I'm sure this question has been asked more than once. How do I know if a jar or container is suitable for making a candle in. Right now I'm using jelly jars. I do have a thick milk glass floral vase I want to make a candle in and give as a gift. I'm concerned about the glass cracking. It is very thick though. I once burnt a candle in an ashtray and it cracked. Thanks:smiley2: