Parabolic reflector

I had an idea for a parabolic reflector, or at least how to make one. I saw a youtube video on making a cement mold, and using that mold with a ferrocement blank to make a dish out of ferrocement.

But I was thinking, that a basic mold could be made with ferrocement, and then spun to have a parabolic form induced. As long as the spinning is kept up till the cement is set, the form should hold. And better yet, if the cement is wet enough, it should have a very smooth surface... The main difficulty should be spinning the mold at a constant speed.

A good look at parabolic reflector based cookers can be found at the solar Cooking website.