The Beer Can Fire Method
Here’s yet another method for starting a fire with a parabolic reflector. The concave bottom of almost any aluminum can (it doesn’t have to be beer) can be used to start a fire with one important modification: It must be polished.
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You’re probably thinking, gee, jewelry polisher isn’t on my list of bug-out supplies. Don’t worry; toothpaste is actually a great abrasive polisher. Simply use a piece of cloth or your hand to polish the bottom of the can until it’s shiny. This may take a while, up to 30 minutes.
Once the bottom of your can is polished to a shine, you can use it much the same as the flashlight or car headlight method. Find the focal point, usually a few inches away from the bottom or the bottom of the can, and hold your tinder as steady as possible. TIP: black or dark colored tinder retains heat much faster and will make this easier.