Today in the Fire Lab we’ll be showing you how to make char-cloth using radiant heat in relatively airtight chambers.
Our first reaction will be on a 2000W digital single induction hob. Its radiant heat zone is wide and shallow by design, and so I am using wide and shallow reaction chambers, also known as tobacco tins.
Fire involves two stages, pyrolysis – where molecules break down under heat – and oxidisation, where carbon meets with oxygen. Here, we ONLY WANT PYROLYSIS.
We prevent oxidisation by keeping oxygen out of our chambers with the miracle of LIDS. The holes in the top are there ONLY so gas under pressure can escape, and those lids will flip right off if we do not use my secret ingredient: a brick
Today, we can tell exactly when I’ve switched my hob on and gone past the point of no return, because that’s exactly when it starts to rain, but the real indicator of success is white smoke pouring out of those holes, and – you will note – out of any other opening it can find.
This is why we use the term ‘relatively airtight chambers’ today. Some oxygen may get in, and some solid carbon may escape suspended in the smoke you see here, but for the most part, everything in our wood and cotton samples that is not carbon is going up and out of the tin, or making a messy resin mess at the rim of any opening.
Because this hob does not offer the same intense heat as a bed of coals, the whole process can take up to 45 minutes, and THEN you have to let everything cool down, including the brick on top, which will get very hot indeed.
But by the time the brick is cool enough to touch, the tins are ready to open and what you SHOULD see is charcoal more or less in the same shape as the wooden or cotton objects that we put in the chamber.
If you see any colour other than black, or if you open the tin and the contents smell acrid, liked burned toast or worse, then the organic molecules have NOT finished breaking down yet, and the evidence is right under your nose.
Also note THIS area right here underneath our vent, where the presence of ASH indicates that a small amount of oxygen has sneaked in during the reaction, causing a further loss of carbon.
For our main reaction today, we are going to use a bed of hot coals, which means setting a fire and waiting for it to mature, and when it does, we will have a radiant heat zone that is hotter AND goes higher, meaning that we can use larger tins.
I’m using travel sweet tins this time: they’re cheap, deeper, and they have snug lids. Note the holes I’ve punched in the lids using the tip of a thick carpentry nail or an awl. Also note the smaller upholstery nails pictured here that look like thumb tacks, but with longer shafts. We’ll be using them to ensure that gas goes out of our vents, but not back in.
Let’s get back to our bed of hot coals, introduce our reaction chambers to the heat, and get some stones on top to prevent our lids from flying off. Do note that in this case the reaction starts almost immediately, and please also take a moment to enjoy the sound of my vents tip-tap-tipetty-tapping.
15 minutes later, the reaction appears to have completed, but rather than waiting for the coals to cool down, we’ll use tongs to remove our chambers from the heat.
Once the tins are cool enough to handle, it’s time to take the lids off an inspect our work. You may note that if gas and resin have been forced out of the sides, then the tops may be a bit sticky.
Inside you will see we’ve arrived at the same result, only faster, and because we’ve taken the precaution of adding a one-way vent cover that lets gas out but not in, we’ve pevented oxygen from creeping in and have NO ash under our vents, and no wasted carbon.
Anyway, that’s how we MAKE char cloth, but stay tuned for our next episode where we will looking at HOW IT IS USED in fire lighting AND comparing the perfomance of char-cloth from different sources. Not all cotton is pure cotton, and polyester is the pits.
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Thanks for joining me in my enthusiasm for fire.