Making char cloth

When cotton is strongly heated without enough oxygen, it does not burn but decomposes. Water and flammable gases escape, leaving almost pure, porous char. Charcoal is made from wood in the same way. Char cloth is essentially the same as charcoal, only in a light, flat form.

The small hole in the lid is crucial. It lets smoke and gases escape from the tin so no pressure builds up, but hardly lets any air in. If the hole is too big, too much oxygen reaches the cloth and it burns to ash.

The finished char is full of tiny pores and so has a huge surface area. That is why the small heat of a weak spark or the point of a burning glass is enough to make it glow. The ember then spreads slowly and reliably – but char cloth gives no flame; for that you still need a tinder bundle.

You need pure cotton or linen, for example from an old T-shirt or old jeans with no synthetic content. Blends with synthetic fibres melt, char poorly and release toxic fumes. Cut the fabric into small squares and lay them loosely in the tin.

The tin should be a small metal tin with a well-fitting lid. Painted or coated tins are unsuitable unless the coating has been burned off outdoors beforehand, because that too produces harmful fumes. Pierce a small hole in the lid.

You also need an existing, safe and permitted outdoor fire and a stick or heat-resistant glove to take the hot tin out. Char cloth cannot be made without an existing fire – that is why you make it in advance and carry it with you.

Place the closed tin in the embers or at the edge of a strong fire. Soon smoke streams from the hole, and this smoke may also ignite as a small flame – that is normal. Keep your distance and do not lean over the hole.

When no more smoke comes out, the charring is finished. Take the tin out with a stick and plug the hole with a twig or a little soil so no air gets in. Let the tin cool completely before opening it. If you open it too early, the hot cloth can ignite in the air and is lost.

Check the result: good pieces are evenly black and still somewhat flexible. Brown pieces are under-charred and catch sparks poorly – they can go back into the tin next time. Keep the finished char cloth in the closed tin or a waterproof bag, because it absorbs moisture and crumbles easily.

Char cloth is made outdoors only, never in the kitchen, on the stove or in the oven. Smoke and flammable gas escape from the hole and can ignite. Synthetic fibres, coatings and paints also release toxic fumes.

The tin gets very hot. Handle it only with a stick or a heat-resistant glove and let it cool completely. Cool burns at once with cool, not ice-cold, running water; for large or deep burns, burns to the face or hands, and burns in children, call the local emergency number (112 in the EU).

The fire you make char cloth on is an ordinary campfire: it must be permitted, needs a safe fire site and is put out completely afterwards. Fire bans apply to it too.

For centuries, char cloth was the usual companion of flint and steel and was kept dry in tinderboxes. It is also useful with friction and solar methods because it reliably turns a small, weak heat source into a stable ember.

Other pure natural fibres or very dry, punky wood can be charred in the same way. Results vary, though; cotton is the easiest and most reliable. Remember: char cloth gives only an ember. A dry tinder bundle and prepared kindling are still needed to turn it into a fire.