When I was a teen, my paternal grandmother gave me an old glass paperweight. She told me it had been in the family (at that time) for around 100 years.
Today it found a new use: firestarter.
I've been talking about firemaking to someone on Steemit who mentioned trying to use broken glass and it got me to thinking. I think it would be really hard to get a focal point from a piece of broken glass, but...
The paperweight seemed like a good potential lens. I have heard of crystal balls on display in store windows causing fires, I'll bet the glass paperweight could do that, too.
Being roughly spherical, the focal length is very short. It actually started burning the tinder just sitting there beside it. You can see the focal point in the top picture-- the tinder was smoking at that point, but you can't really see it in the photo.
I let it burn for a while, and kept adding more tinder dust. Finally, I blew on it and saw that the ember was pretty large, so I put the paperweight safely in the shade, added more tinder, and blew it into flame. That's the bottom picture, but the flames are not visible. Oh well.
I also used it to light some charcloth, and it did so instantly.
Since the photos don't show the process very well I decided to make a video:
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