My wife had a load of burnt-out candles in glass pots, but rather than throw them away it struck me that I might be able to use them to keep frost off the greenhouse on cold nights. All I needed to do was to remake them into new candles.
Melting them down was a bit of a challenge. By putting the glass container in a bain marie I could remove the wax fairly easily, but actually getting the wax melted properly often required sawing the solid wax into chunks an grating it with an old cheese grater. I got there in the end though.
For moulds I used some old bread yeast tins with a little washing up liquid wiped around the inside as a release agent.
Shrinkage of the wax was quite significant though. In the end I was partially-filling the moulds and topping them up several times to stop huge cavities appearing in the wax as it solidified again.
They burnt very nicely though.
So I ended up making quite a few.
On nights when frosts were likely I stood one in a metal dish, lit it and inverted a flower pot resting on a few stones (to allow air in from the bottom) over the top.