My friend and fellow physics teacher, Dan Burns of Los Gatos High School, mentioned using a large Fresnel lens to burn gum off the pavement outside his room.
A few years ago, my school purchased new overhead projectors for the classrooms. I shuddered at the thought of all the old OHPs going to the landfill. I intercepted as many as I could and salvaged the optics from them.
The harvest was bountiful. It included the Fresnel lenses that formed the stages of the OHPs.
Hence the community service project outside my classroom last week.
Two lessons to take away? One: always be on your toes for potential harvests of otherwise unwanted or unused school equipment. (I similarly collected dozens of headphones when the school purchased classroom PCs.) Two: it's nice to have bright folks like Dan Burns to get clever ideas from.