I wrote this article back in April last year for issue 9 of The Bushcraft Journal. If you don’t already subscribe, get yourself signed up!
Solar ignition methods
For this issue I want to look at various ways of lighting a fire using the sun. Right now (last week of April) it’s overcast outside, has been for a few days and is forecast to remain so for a few more, succinctly highlighting one of the weaknesses of relying on the sun in the UK. With that said, solar methods are another tool in your box and worth trying out.
I should also point out that many of the items below aren’t things that I typically carry with me (if it’s an item I do often carry I say so), but are worth knowing about, although I’m mindful of straying into ‘survival territory’ to some degree.
We tend to think of the sun as a yellow ball of fire in the sky but that’s not really the case. The sun is white (it appears to be yellowish due to the atmosphere) and what we think of as burning is actually nuclear fusion taking place. We can use the radiant energy created by this nuclear reaction, and transported to us in the form of photons, to light a fire.
To work for fire lighting, a lens has to be one that magnifies and to magnify it has to have a convex shape. That means that any item with a convex lens can theoretically be used to start a fire. As a general rule, the bigger the lens and the higher the magnification, the easier it will be to light a fire.
With any lens, you need to position it between the sun and your tinder. Move the lens back and forth slowly until the light is focused into a pin prick, giving maximum concentration of the sun’s energy.
A magnifying glass is a hand held convex lens usually with a magnification of between 2 and 6 times, the kind of thing many of us carried around as children pretending to be sleuths. And I’m sure many of you will remember that a magnifying glass could be used for other purposes than making things look bigger. Alongside matches, a magnifying glass was one of my earliest experiences with fire lighting. Here Bob is igniting a piece of chaga.
Strictly speaking still a magnifying glass, but not one that is generally hand held. I’ve got a few 5” lenses, probably from a desk mounted magnifying lamp of some sort. These are very powerful, great for demonstrating how a magnifying lens works but too big to carry around.
Magnifying camera lenses can be used to good effect and are common place. I’m not much of a photographer so got this one from an online auction site; it lights tinder really quickly. In the photo Ho Kyung used a piece of cramp ball.
Fresnel lenses are named after the French physicist who invented them sometime around 1818 for use in lighthouses. Today they are also used in car headlights and traffic lights. The great thing about a Fresnel lens is that it is a series of concentric sections, greatly reducing the amount of material required. I have one that is credit card sized and really light weight; it’s stated purpose is as a reading aid but it makes an effective fire lighter, as demonstrated in this photo by Ho Kyung onto a piece of chaga.
Magnifying glass in a compass
I always have a compass with me when I venture outdoors, and if I’m carrying a compass, it might just as well be one with a magnifying glass built in. The lens itself is small and the magnification is not great, but they will light a piece of char cloth or a cramp ball without too much trouble; in this photo Ho Kyung is using char cloth.
I also always have a loupe in my bag, not so much for fire lighting but because they are brilliant for looking at small things. Try taking a look at a tiny insect or the anatomy of a flower with one, it opens up a whole new world of natural history that I find fascinating.
The one I’m using in the photo is x10 magnification, but I couldn’t get it to ignite either charcloth or crampball. I suspect that might be down to the size of the lens and intend to do some more experimenting with it in the future.
As I said earlier, to create fire with a lens it needs to magnify, so many prescription glasses aren’t going to work, you need magnifying glasses such as reading glasses; the higher the magnification the better (the ones I’m using here are x4). You can also break the glasses and put the 2 lenses one in front of the other to increase the power. In the photo I’m igniting char cloth.
To get the best results from a mirror it ideally needs to be a parabola, which is a 2 dimensional curve, or in other words, bowl shaped. Think of them in the same way as the satellite dish on the side of your house. Wherever the radio waves (in the case of your satellite dish) hit, they are reflected back to a single point. With a parabolic mirror, wherever sunlight hits the mirror it is reflected to one single spot where the energy is concentratd.
I’ve come across a couple of different types made for the job of fire lighting. The advantage they have is that they have a device for holding the tinder at the point where the sun’s energy is concentrated.
I hold them in both hands about midriff height and stand facing the sun. If you’re using char cloth, it will turn a whitish colour when you’ve got it pointing directly at the sun. Ignition of char cloth can be quick, 5 to 10 seconds in direct sunlight is often all it takes.
I’ve found that they don’t work as well when the sun is low in the sky, so first thing in the morning and last thing at night, which is a downside as this is generally when you would want to light a fire if you’re on the trail. I’ve looked into this a little and it appears that at sunrise and sunset the sunlight is reduced by Rayleigh and Mie scattering from minute particles in the atmosphere.
It’s also possible to improvise a parabolic mirror from common items.
Drinks cans have that same parabola shape on the bottom, but the material is often quite dull. You need to polish the underside with a light abrasive to make it as reflective as possible; I recently tried toothpaste but couldn’t get it polished enough and had to resort to using brasso. This isn’t something I generally carry around, but I know some people do carry it for its usefulness as an emergency tinder.
After trying a few different approaches, I found that the easiest way was to put the tinder in a twig which I’d split part way down and then put the stick in the ground in direct sunlight. This meant that I only had to concentrate on holding one thing still. I was then able to move the can backwards and forwards until I found the right spot. I managed to ignite some crampball with relative ease but struggled with charcloth and wonder if this is because there was some wind which meant the charcloth moved around.
Old car headlights are parabola shaped. In fact, they basically work the opposite way to a parabolic mirror in that the element of the bulb sits at the focal point so that any light emitted backwards is reflected in a tight beam. So if you are lucky enough to come across an old car headlight with the bulb still in it, you have the focal point set for you.
Most of us carry LED torches nowadays, but many old torches had a parabolic mirror in them to direct the beam. I tried it out recently with Bob; the plastic lens was glued into the mirror surround and we couldn’t separate them without breaking the whole thing, but Bob gave it a try anyway. Whilst the char cloth lit (surprisingly quickly in fact), we’re not certain if it was from the mirror or the lens. It was also a little tricky to extract the ignited charcloth again.
As a side note, I’ve met several people as I’ve been teaching bushcraft that have told me of incidents involving mirrors in the house that have resulted in severe scorching on window sills and furniture, fortunately no actual fires were caused. These seem to have involved shaving mirrors and make-up mirrors that have a magnifying effect, so be careful where you position them at home as a quick internet search brought up many examples of house fires caused by mirrors.
Thanks to Bob Foster and Ho Kyung Hobeke for helping me out on this one. As usual guys, get out there and give it a try, be responsible and be safe.
We teach how to use lenses and mirrors, as well as a host of other methods of ignition, on our 1 Day Fire Lighting Course, our as well as on our 2 Day & 5 Day Bushcraft Courses, the IOL Bushcraft Competency Course and also our 2 Day & 5 Day Survival Courses.