Last year I ran out of my waxed dirt. In a pinch you can take a
block of wax and put it in a vice, then run a wood plane over the
top. Put a tray or piece of clean cardboard under this to collect
your shaved wax.
Last year I got in a rush. I didn't know it, but apparently I burnt, my dirt or wax, contaminating it. I didn't catch much with that
batch, and unfortunatly I had put out alot of sets before I figured out my problem. There is a fine line there. Too much heat and your dirt is no good. Not enough heat and your wax won't melt.
I will try the double boiler method. That sounds sane.......