Start with 2 nesting cans, tuna cans are shown here. The object is to let hot gasses out while keeping air from getting in.
Step 2
Cut up some 100% cotton cloth into pieces small enough to fit into the can. The pieces will shrink as they turn into charcloth. I filled the can all the way. If you use less it will take less time. This is old blue jean material from a pair that ripped on me one hot summer afternoon while working.
Step 3
Stack the material into the can. Pieces that are too large can be folded. You can even cram them in if you like. It does shrink during the process. Be sure you use only 100% cotton material (not blend).
Step 5
Heat thoroughly until smoke or flames no longer come out of the container. Here you can see the gasses from the cloth burning as they come in contact with air. 3 or 4 pieces of t-shirt material will only take about 15 minutes. I checked this at 30 minutes and it was not quite done (all black). I then forgot about it for over an hour and returned to see no smoke or flame coming out indicating it was done. When the process is done, remove from the flame (be careful to not let the top can come off and let air in) and let cool.
Step 4
Place the top can over the bottom can with the cloth and set over an open flame (even a campfire will suffice). Be sure the seal is still intact between the upper and lower can.
Step 6
Once the cans are cool, remove the top can and pull out the charcloth. It is now ready to use for a fire piston, flint & steel, ferro rod, bow and drill, or solar lens to create a glowing ember to place in your bird-nest tinder (I use it in my new fire piston). It tears off easily to create the size you need.