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Re: making a spherical mirror
To make a simple parabolic mirror, use a large pot, reflective mylar, and a vacuum pump.
Stretch the mylar over the open end of the pot, and use the vacuum pump to evacuate the air out of the pot. (You won't ever cook out of this pot again, as you'll need to drill a hole in the side/bottom of it and weld a plumbing fitting onto it to pump all the air out.) As you pump out all the air, the mylar will be sucked inward due to the ambient atmospheric pressure and will form a parabolic mirror.
This method will be less "permanent" than pouring epoxy into a spinning mold, but it would be easier to produce a highly reflective surface. With this method, it would also be possible to vary the amount of air you remove from the pot (and hence the focus point of the mirror).
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