Using a magnifying glass for fire starting takes me back to the days of burning ants as a child (and getting in big trouble for inadvertently igniting the old rotten stump in the backyard). Optical fire starting is one of the easiest alternative fire starting methods, once you understand it and have the right materials and conditions. This method requires that you concentrate strong sunlight through a clear lens or with a curved mirror (like the mirrored cup in a large flashlight). When this concentrated sunlight forms a blinding, white-hot point on some suitable tinder, the flammable stuff will start to smolder. The red ember you created can then be blown into flame when combined with more tinder. Sounds easy, right? And it can be, if you learn to use a magnifying lens more effectively by lighting fine fibers, dark tinder, and char cloth.
Use Fine Fibers
Coarse tinder abounds in the wild. Dry leaves, pine needles, bark bits—these all can light under the warm embrace of a match or lighter, but they’re not that friendly with optical fire building. You’ll have better luck if you switch from solid surface items to something finer and fluffier. Grab some fibrous dead bark and shred it to expose more fibers or try some weed tops with fluffy seed down. These fine materials will be easier to ignite than more “solid” material, and increase your chances of success in hazy weather.
Pick Dark Tinder
Ever pet a black dog on a sunny day? His dark fur will seem almost hot to the touch. Dark colors are better at absorbing light and becoming hot. Don’t believe it? Try to light a white cotton ball on fire with a magnifying glass. It’s not that easy, as the white color bounces away light and heat. Collect darker tinder and watch your results go up in smoke—in a good way.
Try Char Cloth
The same char cloth you’d use for traditional flint and steel fire starting is the ideal tinder for optical fire starting. It has a low ignition temperature due to the charring process. It’s also black, so it readily absorbs heat. And it gives you a decent burn time, allowing you to place it into tinder and blow it into flame before it dies out. Char cloth can be made by placing cotton, linen or fluffy tinder in a metal box or can with one tiny vent hole. Toss this can in a campfire and let it cook for 5-6 minutes or until smoke stops jetting out of the vent. Use a stick to roll the can out of the fire and allow it to cool before opening. The resulting material should have become black and it should have shrunk in size a little. It should also be excellent at catching sparks from ferrocerium rods, flint and steel, and optics. Test it with a few sparks, just to be sure. When the char gets red spots from the sparks that hit it, you did everything just right. Store your char in the can, or in another dry container with your fire starting gear.
How do you light fires with optics? Please tell us your method and source of tinder by leaving a comment.