Skeggley,
One of the nice things about using a solar wax melter using a bottom filter dripping into a pan below is that once the wax is hot enough to melt, it drops into the pan below out of the sun, it starts to cool. You can tell this because the wax builds up in layers and does not melt to the point that the impurities separate out. They are locked in the middle. Also the bottom of wax is not flat, usually it is little balls stuck together.
Jim Altmiller