Joshmartinez wrote: letting a candle melt in a jar top
I'm confused, are you saying IN a jar top or ON a jar top??
If you are speaking of a honey jar, for instance, your ingredients are in the jar and the lid is sealed on the jar, candle goes on top. (These can be ongoing replacing the candle as needed), no lid I have ever seen had an issue. I wouldn't use a painted lid though.
You could put a tea light on top they are pretty self contained, some tapers might be treated with fire retardant at the bottom, this is to prevent glass/crystal holders from breaking.
When you said IN the lid, I wouldn't do that ...most lids are treated with plastic to get a good seal, and you could release toxic fumes if the plastic starts to melt.
Get a large flat terra cotta dish (the kind for placing under a flower pot) and do your burning work on that on the stove or in a fireplace.
Also I would suggest working with fire some. Light candles, build a fire, burn some paper...in a pit outside. Sounds like you could do some experimentation to see fire in action before questing upon a fire spell.