Giant Fresnel Lens, Magnesium, and a little bit of Thermite 

My friend’s old big screen projection TV died, and he gave me the screen from it.  The neat thing about big screen TVs is that one layer of their screens is a Fresnel Lens.  People have used these for starting fires and lots of other stuff, and we figured we’d join in.  Ben wanted to try making thermite, so we decided to try using the Fresnel Lens as the ignition source.  After making a crude frame and lining it up with the sun, we were able to light magnesium (from the lower casting of a broken mountain bike fork) on fire quickly and easily.  According to Wikipedia, Magnesium’s autoignition temperature is 883F!

The thermite was home made, thrown together the night before from rust powder from an old bucket of metal junk and aluminum shavings made with a hacksaw.  We didn’t have much success actually lighting the thermite, but we did manage to get a couple tiny blobs of molten iron.

We did this at the end of May 2012, here’s the video: