Here’s my experience……putting dirt under glass to melt wax, you’ll see the glass sweating, condensation forms, doesn’t seem to work.
I’ve found the easiest way is to heat dirt /with wax is with a propane turkey cooker stand with a bottle of propane. I use an old canner to heat up dirt with wax. A microwave works well too, for small batches. If you have access to a cement mixer and a good heat source, even better.
I know that you can use sunlight to melt wax into dirt…..but I’m done with that method. It never worked out for me.