>I am thinking of making a solar melter. > >I understand that the design is nothing particularly difficult, but I >wonder if >there is any necessity to use glass on top, or if plastic will work as well -- >assuming it does not melt. Several modern plastics, e.g. polycarbonate or modified acrylate with glass fibres cast in, will certainly take the heat fine - I have used them on solar water-heaters, which run somewhat hotter than a solar wax-melter, and they last many years developing only slight cloudiness. But scrap plastic of suitable area is generally harder to come by than scrap windows. And if it is non-flat - say, corrugated - you will have to fit it to a frame of some sort. I see no point. In many places, it will be easier to get a 'demolition' window, complete with hinges or at least still having an entire wooden frame onto which hinges can be screwed. Any wooden cross-members are a non-problem; the incoming solar radiation is hundreds of watts per square m, and even if the box under the glazing is just a big drawer or other simple wood container, with no special insulation, the wax will melt within a few hours. This is not a case of needing to maximize efficiency; considerable losses can be comfortably tolerated. Of all functions that can be subserved by solar energy, this would be one of the most clearly ahead of all rivals. Go solar! R