More Solar Fire Tricks with a Soda Can

Okay, on the advise of a bunch of online sources and videos you’ve worn yourself out trying to use a chocolate bar to polish the bottom of a can to make a solar fire starting reflector–or, wisely decided to eat the chocolate instead. If you have no fine steel wool or or other fine polishing agents for aluminum, it may be time to look around for shiny Mylar wrapper–maybe from the chocolate bar. It’s the shiny silver plasticized stuff now being used used to package more and more things. Pop Tarts, granola bars, raisins, trail mix, energy bars, cough drops, coffee–you name it.

Or, if you happen to snag one of those shiny Mylar foil blankets originally billed as Space Blankets that were suppose to keep you warm in an emergency–cut off a small piece of that; it is probably already torn anyway. If you are still determined to try to make fire with your aluminum can, as a more promising alternatives to polishing the actual surface of the can bottom, instead, just use the surface as a form for the Mylar. That is, just use a piece of the shiny silver Mylar wrapper to line the bottom of the pop can–molding the stuff into a parabolic reflector.

Cut the material into strips and piece it onto the parabolic surface of the aluminum can. It can be glued in place with any number of naturally sticky things. Sugary sap from trees or fruit, syrup, pine pitch, bubble gum–whatever. It just has to help the Mylar pieces to lay flat and deemphasize the seams. The picture below illustrates how forgiving this method can be. Granted, it took a while to light a piece of char cloth with this can in late afternoon sun, that I had temporarily given up before I realized it was already on fire, but if you take care to make the Mylar as wrinkle-free and seamless as possible, it works much better. This is often much faster than trying to polish the surface of the can without the proper materials.



Here, I used a Hershey’s white chocolate candy bar inside wrapper. Better to eat the candy and do this than waste the candy and the effort trying to polish the can sufficiently to make fire.

I tried this method while making several other videos last summer. I was tired, the sun was about to  go down and I was going to wait for another day. I had already tossed the piece of char cloth I was trying to light into the refuse can, when I realized it was on fire. I had not seen it in the bright sun with the sun blowing the slight smoky smell away from me. It is not uncommon under such circumstances to fail to realize the char cloth is alight until I burn my fingers. I mention this primarily as a safety caution, to always carefully dispose of such even if you think it is out.

I should also emphasize that having the right kind of tinder can make the difference between supper cooked or raw. Char cloth,tinder mushrooms, or similar tinder is important for this to work when the sun’s rays are compromised by angle, season, or thin clouds. There is a previous post within this weblog that tells how to make char. There are also extensive discussions regarding char cloth and other alternatives at my larger blog, One hundred Ways to Start Fire without Matches, linked at the bottom of this post.

Good tinder will greatly increase your odds of getting fire. Partially burned, carbonized materials called char or char cloth is usually the most easily obtainable and reliable material. If you have no idea of what this stuff is, I suggest that you read my previous post regarding types of tinder and how to make or find them. I have my own ideas, techniques, and methods about this, but there are various directions all over the Internet these days. Having the right kind of tinder can make the difference between supper cooked or raw.

The final piece is understanding how to use the reflector to direct the sun’s rays in relation to the tinder. There are a few ways to approach this. Each parabola has a set focus. The focus is the point at which the reflected rays converge for the maximum intensity. This can be determined mathematically or it can be found by trial and error. In the case of aluminum beverage cans they seem to at about the same point. It is located directly above the center of the bottom of the can about as high as the radius of the bottom of the can. (The radius is half the diameter.)

When you point the parabola directly at the sun to take full advantage of the entire parabola surface, you have a logistics problem of having your fingers cast a shadow over the whole thing. One solution I to punch a very small hole right in the middle of the parabola can bottom and pushing a thin piece of wire or paper clip or stick through from the other end. You can then perch a small piece of char tinder on the protruding piece of wire and adjust it to visually view the sun striking the tinder.
When the rays are the converging rays are at the smallest and brightest point–bingo. That’s where you want it to be. It doesn’t take long to get smoke if all other conditions are right.

Another way to enhance your chances of lighting your tinder is to hold it steady by facing toward the sun so that you can easily point and steady it with your arms or hands braced against your sides without your shadow getting in the way. Sitting comfortably with your back against something or with your legs crossed pow-wow style works pretty well. As you point the can at the sun you can visually position it until it until you see the sun reflected at the center of the bottom of the rim of the can. With this technique you are not trying to find the exact focus of the parabolic reflector. You are reflecting the sun to the bottom side of the can. It will not be a uniform beam, but will appear elongated and slightly more narrow and brighter on the side nearest to you.

Once you maneuver into a position that allows you to direct this offset beam and hold it steady, you will need to get a small piece of tinder in position at the brightest tightest point. If sitting, you may want to place it on the ground to keep it steady. I I find that it is easiest to concentrate the beam at a point and once set to move the tinder into the beam rather than trying to find the tinder with the beam. I also sometimes place the tinder above my knee on my crossed leg where I can sit comfortably and direct the beam while steadily bracing to keep the beam in place.

Once everything is in place with the concentrated beam steadily trained onto the tinder, it may take as little as ten seconds or as much as thirty seconds to get smoke. If you are using char cloth, it will quickly form an ember and continue to burn while you move it to your prepared larger tinder bundle and fan or blow it into flames to start your fire.

As with virtually any other skill, once you have gone through the process a few times you will find your own groove and what works best for you. Nothing is very easy the first time around. Don’t get discouraged or be put off if it seems too complex or seems to require too many steps. It is actually much harder to describe than it is to do. I try to include sufficient instructions to cover all contingencies. This is one of the easiest and most amazing ways to start fire when the sun is out. The frustration that I hear so much about and the skeptics and fails that are prevalent on the Internet are from those who simply don’t know the techniques shown here.


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