A good while back I wanted a nice old style headlight, but couldn't afford one. Didn't want the weight of it on my bike either, but I did want that 5.25 inch wide lens.
So, I made one. Took a chunk of ash wood, put it in the lathe, and turned it to the profile I wanted, then used that male blank to cast a female blank with plaster of paris mixed with chopped glass fiber insulation in an old asphalt can. Once that cured up, I painted both blanks with 3 coats of oil based epoxy, sanding with 000 steel wool between coats. Then I put them in the oven overnight on "warm".
When they were both ready, I took a photo offset printers plate, and mounted the female mandrel to the screw feed tailstock of the lathe, with the male on the headstock, plate between them. Started the lathe on its lowest speed (300 rpm) and started advancing the female mandrel, trickling light oil (canola, actually) into the joint as I advanced. Took about ten minutes, but when I was done I had a conical headlight shell. Shaped the lip with a dremel and careful crosspeen hammer work, and mounted a 12 volt landing light bulb and reflector in it, lens was off the landing light as well..
Worked great.