Flint and Steel: What Causes the Sparks?
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Starting a fire with flint and steel brings to mind the image of self-sufficient mountain men in the wilderness. A rite of passage that ties you to wilderness travelers through the millennia, the ability to use flint and steal is one of the basic survival skills everyone should master.
But how does flint and steel work? More specifically, what causes the sparks when you strike a piece of flint with steel? The answer will surprise you!
The following information will help you understand what it takes to make fire using flint and steel. It will change the way you look at flint and steel as a fire making tool and perhaps even make you a better flint and steel fire maker.
Survival Topics believes that if you know the fundamental reasons why survival gear and survival techniques work then you are in a far better position to use them to best advantage.
The Secret of Flint and Steel for Making Fires
Outwardly the answer seems obvious; striking flint with steel produces hot sparks. However, dig a little deeper and you will find there is a lot more to it.
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Flint and Steel A typical high carbon steel and flint used for making sparks |
What many people do not realize is that iron is a pyrophoric material; in the presence of oxygen, iron catches on fire automatically! It just starts burning.
“But how can this be?” you may ask. “I can hold a chunk of iron in my hand and it does not burn me”.
The answer lays in the fact that the portion of the iron object in contact with the air and your skin is not pure iron. Rather it has developed a thin coating of iron oxide, or rust, immediately upon contact with the oxygen in the air. This serves to seal off the iron inside from exposure to the air and reduces the rate of further rusting.
Iron, whether man-made objects or naturally occurring in rocks, will rust upon exposure to oxygen in the air. The act of rusting is actually an exothermic reaction called “oxidation”, which is a fancy way of saying when iron touches the oxygen in the air a reaction occurs; the iron rusts (turns into iron oxide) and gives off heat. In other words, it burns.
A fresh piece of iron spontaneously ignites upon contact with the air
The simplified chemical reaction can be expressed as:
Fe2 + O2 = Fe2O3 + heat
Or in English:
Iron + Oxygen = Rust + Heat
Rusting (oxidizing) is the exact same thing as burning, but unlike a campfire usually you will hardly notice it. Because of the relatively size of a typical iron object, the heat it gives off as it rusts dissipates too quickly for the heat to accumulate and be of much use.
While holding an ordinary iron object you are unlikely to feel any heat as it rusts, since the heat is absorbed by its surroundings as fast as the oxidation process produces it. However if you can increase the oxidation you can cause the iron to spontaneously give off a large amount of heat very quickly.
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Smaller Pieces Have More Surface Area As can be seen in this illustration, the total surface area of the smaller cubes greatly exceeds the surface are of the cube taken as a whole. When a tiny particle of fresh iron is broken off from the main mass, the surface area of the particle is very large in comparison to its total size. Upon contact with oxygen in the air, the tiny iron spontaneously ignites (also known as rusts or oxidizes) and glows red hot. Use this red hot spark to start a fire. |
Increased oxidation can be accomplished by breaking off smaller particles of iron from a bigger piece. The smaller the iron particle is, the greater its surface area compared to its total size.
Now you know the secret to using flint and steel to start a fire:
If you can create a small enough particle of fresh iron, upon contact with oxygen in the air the iron particles increased surface area will oxidize faster than it can dissipate the heat formed during the reaction. The result: the particle of iron spontaneously becomes so hot that it glows as it oxidizes – and can be used to catch tinder on fire.
In a nutshell the process of using a flint and steel to start a fire works like this:
- Find a piece of high carbon steel, which is about 98% iron and 2% carbon.
- Find a piece of flint or other hard sharp object such as quartz.
- Strike a sharp edge of the flint a glancing blow with the high carbon steel. Doing this just right takes practice.
- Very tiny particles of fresh iron fly out from the steel.
- Upon contact with oxygen in the air, the surfaces of the iron particles spontaneously ignite and give off heat as they oxidize (rust).
- Because the surface area of the iron particles is so large compared to their volume, the particles quickly heat up and glow red hot. They become sparks.
- Catch the sparks in prepared tinder and use it to start a fire.
Best Flint and Steel
Iron by itself is relatively soft and tends to bend rather than chip under the stress of a hard blow on a piece of flint. To make iron harder for use in industry, it is made into what we call steel by adding some carbon. However by making it harder, the steel is also becomes more brittle.
The harder a piece of steel the smaller the pieces of iron broken from it will be when struck against a hard sharp object. As discussed earlier, smaller pieces of iron will spontaneously burn hotter due to their increased surface area.
Another way to get hotter sparks is to break off smaller pieces from the steel by striking it against a harder, sharper object. This is why you need to keep the edges of your flint very sharp for optimum creation of hot sparks when striking the steel.
In short, harder steel and sharper flints give hotter sparks.
Flint isn’t the only mineral that will cause sparks when steel is struck against it. Any hard stone with a sharp fracture can be utilized as long as it can break off very small pieces of steel.
Advantages of Flint and Steel
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Iron Burning Upon contact with the air, a shower of tiny iron particles spontaneously catch on fire |
Starting a fire using flint and steel takes a more expertise and preparation than simply striking a match, however many survival experts feel this disadvantage is overcome by the fact that a wet or damp flint and steel can still be used to start a fire, and that a flint and steel can start many thousands of fires without wearing out; both very important attributes when surviving in the wilderness.
Try carrying tens of thousands of matches in the wilderness or stockpiling thousands of matches in your disaster preparedness kit! Even if the shear weight and volume of your matches do not discourage you, you are also faced with the problem of keeping them viable from dampness or the ravages of time.
Flint and steel overcomes these problems and provides the survivor with means of starting a fire that is more reliable than matches - if he is skilled enough to use it.
Modern Flint and Steels
Swedish Firesteel is a special type of “steel” that more readily oxidizes than carbon steel. Typically in rod form, this type of firesteel produces a massive shower of very hot sparks by simply scraping it with a sharp object, This makes fire starting easier than when using traditional flint and steel.
Survival Topics offers Swedish firesteels at special rates for its readers. For more information see the Survival Topic Swedish Firesteels.
Canada
Great website, and interesting topic on this article. While you are correct about the exothermic reaction of the oxidation of iron, you should look into the even more exothermic reaction created when carbon oxidizes.
The reason why you need "high carbon" steel (or iron..which is usually around 3-4% carbon as opposed to high carbon steel which is 0.4% carbon) is for the carbon.
When you strick/hit the carbon, the resultant energy from impact/friction heats up that small area enough to create the C+O2 --> 2CO --> CO2 exothermic reaction. This is the basic premise of oxygen steelmaking and the source of most of the energy required in this process.
So, yes, the iron oxidation does create some heat, the vast majority of heat and spark actually comes from the carbon oxidation.
Try doing the same thing with low carbon or mild steel? Doesn't work? But there's iron present??? But not carbon.
Keep up the good work on site, love the VERY useful info on survival and I've actually passed along some of it to family and friends! (along with the link to your site!).
Great answer and very infomative, thank you.
North Carolinia
i am doing a project and this information on what causes sparks has been of very good help.
Great job explaining how flint and steel works. I am interested in making a few strikers. what is a good, cheap, easy to find, and easy to make metal striker besides old files?
San Diego
I am no metallurgist. But a simple, primitive and basic way might be to smelt iron ore (like rusty red dirt on the surface of the earth) with wood charcoal and bellows. The charcoal gives the needed carbon. To make charcoal we might use oak wood, as it burns hot. Flat stone could become a simple furnace where ore would be melted by mixing with charcoal. Air flow helps to melt the ore and remove impurities. The refined molten iron could then be carried down a grove (maybe made in sand) into a mold (also made of sand) creating ingots of pig iron. When cooled strike the ingot with a flint rock (obsidian works also) chipping off a small piece to make a spark. With enough practice in these things a person might gain the skill necessary to aim sparks toward kindling and start a nice fire for warmth in cold weather, keeping wild beasts at bay, cooking, etc.
You are welcome to share this Survival Topic with others. I only request that you use a short blurb (not the entire survival content) and this code to
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So if you processed iron into small fragments in a vaccuum and then introduced air, you'd have a lot of sparks?
Survival Topics: Tim, ultrafine iron particles of 5 microns or less are pyrophoric and can ignite spontaneously in air.