In my previous entries I talked about how all fires need a fuel, oxygen and heat in order for the chemical reaction that is a fire to take place. In this entry I will be looking at how we provide the initial heat needed to start the reaction and create a fire. There are numerous ways of creating a spark or a flame, such as matches and lighters, but in this blog I will only be looking at the method we used in the woods which is fire steels.
Fire steels, or flint and steels, have been in use in some form or another since around the start of the Bronze Age, however the concept has remained the same. Flint and steels work by using a hard rock, commonly flint or quartz, or metal to strike sparks from a piece of iron or steel. Before iron working became commonplace, iron pyrite was often used. This theory was proven by the discovery of a prehistoric mummy, known as Ötzi carrying a fire kit which included fungus with particles of Iron Pyrite embedded in it. Modern flint and steels use a ‘flint’ made of steel and a ‘steel’ made of an alloy called Ferrocerium comprising of Mischmetal an alloy of Cerium, Lanthanum, Neodymium and Praseodymium, which is blended with iron for strength. To create sparks, the steel is struck with the flint at an acute angle which creates sparks. The steel is held in such a way that the sparks should land on a tinder, or material that can easily be ignited through use of sparks or a match. Common examples of materials that can be used as tinder include: paper, cotton wool, wood shavings, rotting or charred wood, cloth and some types of dried fungi. The most commonly used fungi are Chaga, Amadou (Horses Hoof fungus) and Cramp Balls (or King Alfred’s Cakes)
We now know how flint and steels are used, but how do they work? The friction of shaving these shards off the steel, and the pyrophoric nature of iron and steel (Pyrophoric materials are substances that spontaneously combust in air at or below 55 degrees Celsius), provides the heat needed to create ‘sparks’ which are actually extremely small pieces of molten metal. If you have ever seen someone using a circular saw or grinder on metal, the sparks you see are created through exactly the same principle. You may be thinking ‘iron can’t be pyrophoric, none of the iron I see spontaneously combusts!’ but in fact the iron you see isn’t pure iron! Most iron products are either alloyed with something to given a coating to prevent rusting, which also prevents combustion! This is because, as we saw in the last entry, rusting and burning are the same reaction.
Rusting and burning are both exothermic oxidation reactions, which means both chemical reactions involve a substance reacting with oxygen to produce a by-product and heat. The chemical reaction for this is 2Fe2 + 3O2 = 2Fe2O3 + heat, or Iron + Oxygen = Iron Oxide (Rust) + heat. Because rusting occurs at a much slower rate than burning, even if you held a piece of iron in your hands the heat produced would have been absorbed by its surroundings before you even felt it. The reason sparks glow is due to their large surface area. Because so much of the particle is reacting, the heat builds up in the particle, causing it to glow red hot.
While using a flint and steel takes more skill than using matches or a lighter, they are much more convenient. They can be used hundreds or thousands of times before they need replacing, they still work when wet or cold, and take up less space than the equivalent number of matches or a lighter and fuel. They are also much harder to damage than matches and lighters. In cases of emergency, it is even possible to improvise a flint and steel, using a tent peg and a knife or rock! As always, I hope you have enjoyed learning a little more about our world, and please ask if you have any questions!