First task was starting a fire. No simple task when everything is soggy. I’m getting better at this – I used an old scrap of linen this time. Obviously, what I need is appropriate, dry kindling, but despite it being a dry winter, the moment I start using the site, it’s been wet. This is partly why I’m so interested in charcoal, and its cousin, charcloth – even if each fire only makes enough dry material for the next fire, it’s a step up from starting with wet wood. Charcloth works on the same basis as charcoal – you use heat to drive off any volatiles, leaving mostly carbon behind. In my case, I used some old denim fabric, but any natural fabric should do the job. I suspect that even leather might work, and I want to try it soon. The fabric was placed in a tobacco tin with a couple of small holes in it. I placed this inside the charcoal tin, but it should in theory be possible to do it directly in the fire, although controlling the temperature and available oxygen will be harder to do.
Thinking of larger yields, I’m starting to plan for a bigger charcoal burn, but this will take plenty of preperation, and at least 12 hours to control the fire and make sure it is safely depleted at the end. We’ve got an old metal drum – this one doesn’t have a lid, but I intend to bury it on its side, and then cover it with soil to block it up. I’ll talk about that in a future post.
Getting back to the present, I made a bit more effort to heat the charcoal tin from all sides; it wasn’t fully in the fire, but one side was, and I rotated it from time to time, to ensure an even temperature. This time, I think I achieved about 90% conversion, with only a few pieces that were not fully pyrolised – those had been shielded by the smaller charcloth tin.
The other task for the day was extracting tannin from tree bark. To this end, I used some rebar to build a frame, and suspended a large wine pan over the fire. This was filled with water, and left to boil. The mistakes I made here are legion. Next time, I’ll lower the level of the pan. Then I’ll build a much larger fire, and only put the pan over it once there is a significant bed of embers. It will also be worth adding the bark first, and then the water slowly
Anyway, I went to find some bark. At this early stage, I’m unhappy about attacking trees, and there’s a problem with tannins – they are water soluable, so any deadwood bark will be heavily depleted by rain. I’ve found a couple of trees with loose bark, that I was able to pull off easily. These trees are sycamores, so they don’t have the best tannin content, but a lot of the reason for working in this way is to establish the processes; I can worry about the best tannin content later! I’m also loath to damage healthy tree bark until I know that it’s worth the hassle.
Tannins will be familiar to most of you in leaf tea, where they are known for their cleansing and antibacterial properties, but what I’m after is a much stronger, and more toxic, “tea”, of the sort that was traditionally used for the tanning of leather, but is also useful for treating wood and steel, and for my purposes, it’s free and easy to make.
The results weren’t too bad – I got a brown liquid, which I improved over several sessions by re-boiling the bark and liquid, and adding some additional bark. The leftover bark is good for firming up muddy ground, so nothing goes to waste. I’m not sure how I can test the tannin content of the liquid – it might require some actual leather tanning to see if it works, but that’s a long way off. I will take my pH testing paper at some point; the tea is sometimes called “tannic acid”, but it’s not a true acid, so I don’t know how it will show up on the paper.
The charcloth worked really well, better than I could have hoped. I achieve 100% conversion, and the resulting fabric holds together, but can be torn up easily. It’s like a fire-lighter, so if you can generate a spark, the charcloth holds it well, and can be bundled with a bunch of kindling, and blown on to quickly create a fire. A later experiment, where the whole biscuit tin was filled with charcloth was less successful – the outer fabric seemed to insulate the inner layers, which were hardly effected. This is surprising, as the outer layers were so hot when I opened the tin, that they all started to smoulder! I hastily put the lid back on – this was the effect of the oxygen reaching the hot, partially-converted charcloth.
This is turning out to be one of the big problems for me – a lot of these hot processes need a strictly controlled supply of oxygen (or no supply at all), but the residual heat means it is hard to check the results the same day as the experiment. As I’m only here once a week, this slows my progress down considerably.
The next post will look at clay processing.
Latest posts by Jamie Hall (see all)
- Book Review – “Mappae Clavicula, A little key to the world of medieval techniques” – translated by C. S. Smith and J. G. Hawthorne - April 26, 2015
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- Book Review – Art of the Anglo-Saxon Goldsmith - March 28, 2015