When you burn a match, lots of things happen. The tip ignites, along with the stick, and sometimes the head of that burnt match becomes magnetic. What causes this weird phenomenon? The tip was once made of phosphate, but these days it’s usually phosphorus sesquisulfide and potassium chlorate, among other ingredients.
None of these substances are made of iron or other commonly magnetic metals, so clearly something odd is going on. If you haven’t seen this strange effect before, grab a match and a magnet and give it a try. The results are surprising. You can try sticking an unburnt match to the magnet first, but there’s little result since it needs to burn up before the magnetism is noticeable. I’ll explain what’s happening and why this weird science works.
Why do burnt matches become magnetic? Matches are magnetic because of a small amount of iron (III) oxide in the tips. Because it’s scattered and tiny particles, this iron is weak before the match burns. However, the chemical reaction present during burning causes this iron to become metallic iron. Thus you get a burnt match that sticks to a magnet because the tip has iron.
How Do Matches Become Magnetic
Not all matches are magnetic after they burn, but most are. The tips contain a small amount of iron (III) oxide, otherwise known as rust. Having this in the mix helps create the common red tip on your matches.
Along with phosphorus sesquisulfide and potassium chlorate, the iron (III) oxide and a binder come together to form that tip. Because of the coloration of rust, namely reddish-brown, you might expect red-tipped matches are more likely to become magnetic than their colored companions. However, ultimately it depends more on the content than whether coloring agents were added during manufacture.
The particles of iron (III) oxide in your match tips are scattered and weak. Resultantly, you cannot simply stick an unburnt match to the nearest magnet. Yet a strange thing happens during the chemical process of burning. The carbon reduces that iron oxide into metallic iron. As fire burns, it uses up the oxygen and pulls the ‘oxide’ out of the iron.
Moreover, the resulting elemental iron is ferromagnetic. The short explanation is that this means it’s very strongly attracted to either end of a magnet. So, burning a match makes the rust in the tip come together, change chemically into iron, and gives it a strong magnetic reaction.
Color Is a Cue
When matches burn, you’ll notice they almost always have a yellow flame. This is an indicator of a reducing flame or low oxygen burning state. Seeing that yellow fire means that any iron (III) oxide inside is turning into elemental iron as it burns. The metal itself isn’t providing any fuel for the fire, but the oxygen molecules bonded during oxidation (rusting) feed that blaze.
Most fires burn yellow, at least partially. This is telling you that the fire has unburnt carbon particles. The carbon isn’t consumed completely, and it glows. Intriguingly in zero gravity environments like space, flames are not tall and yellow. Rather, they tend to be rounded and bluer because they burn more efficiently without the drag of gravity, weighing it down.
Another color cue comes from the tips of your matches. Red tipped matches are the most likely to contain iron (III) oxide because it is commonly used as a pigment. The reddish color is easy to obtain and plentiful, so it makes a good coloring agent. Although it’s still possible to find iron (III) oxide in non-red-tipped matches, there’s no real need for it, so white and other colored match tips will often lack this odd magnetic effect.
What Are Matches Made From
Match heads are magnetic after they burn, but the bodies are not. So what is a match made from that causes the disparity? Well, the bodies of most matches are wood or paper, and since both those products are made from trees, it’s easy enough to see why the end you hold isn’t magnetic. Wood isn’t magnetic.
As for the tips of matches, the composition varies, which is why only some matches are magnetic after you burn them. Most safety matches are made of a blend of chemicals, including a binder (glue), phosphorus sesquisulfide, potassium chlorate, and a coloring agent. You may find unique matches with blue or green tips, but most are red from the iron (III) oxide used to color them. Hence the magnetic iron comes from the tip.
Originally all matches were ll made from white phosphorus. While these matches were highly flammable, they were also highly toxic. Workers in match factories became ill and died in many cases. Moreover, they suffered from horrible, painful, and disfiguring jaw degeneration. This eventually led to an uprising of factory workers. However, it’s interesting to note that at least one company was producing a safety match, which was less damaging to workers before this happened. Sadly, people didn’t want to buy safety matches because they were harder to strike.
The flammability of white phosphorous matches caused more damage than the workers. Because it was so incredibly easy to spark, many fires resulted from the original and incredibly dangerous formula. After the worker uprising, white phosphorous was no longer used. The new formula containing phosphorus sesquisulfide became the standard, and the formerly white or off white match tips got their color from the iron oxide inside the new blend.
Why is Manganese Not Magnetic
The manganese in match tips is often mistakenly cited as the cause of the magnetic effect of burnt match tips. However, manganese is not magnetic. The confusion likely stems from the name. the word manganese comes from the Latin word magnes, which means magnets.
Pure manganese is highly flammable, so it makes a good component for match tips and other products such as fireworks which need to burn easily. On its own, manganese can react to oxygen and burn. You’ll find it in everything from soil to vegetables, making it readily available just like iron. In fact, it’s the fifth most abundant metal in the earth’s crust, meanwhile iron is the number one most abundant metal on our planet.
The potassium chlorate in match tips reacts with manganese to release oxygen gas. This thermal decomposition helps fuel the flame. The same reaction is often used on a larger scale to benefit labs and schools since it is a cheap, relatively safe, and effective way to generate O2.
Not All Iron Is Magnetic
While burnt matchsticks are magnetic, it may surprise you to learn that not all iron is magnetic. Likewise, there are some varieties of steel which are non-magnetic. Though steel contains iron, a good example of this phenomenon is 304 stainless steel. This particular blend is made from three magnetic metals, iron, chromium, and nickel. However, it usually contains atoms arranged in a face-centered cubic (fcc) lattice, which creates a non-magnetic alloy. The microscopic shape makes all the difference in magnetics.
As for pure iron, it also comes in magnetic and non-magnetic forms. The microstructure and crystalline state determine whether this metal is magnetic, and those are affected by heat. According to Thoughtco, “…a substance needs a magnetic dipole moment in order to be a magnet, which comes from atoms with partially-filled electron shells.” Dipoles in magnets typically align below 770 °C, but when heated above that temperature, the crystalline structure changes and becomes paramagnetic instead. In short, superheated metals aren’t attracted to magnets.
There Are Metals That Are Not Magnetic
Most people assume that all metals are magnetic. Oddly enough this isn’t true. Only those metals with some iron, nickel, cobalt, gadolinium, terbium, and dysprosium content are attracted to magnets. There are also about fifty that don’t stick to your magnets as well. Examples of this include aluminum, copper, titanium, silver, mercury, and platinum.
These metals are nonferrous. In other words, they don’t have any iron content at all and as a result, they are not magnetic. Tin however can be either ferrous or nonferrous, and thus it belongs in a special category on its own.
Final Thoughts
There aren’t many things that change from a non-magnetic state into a magnetic one. Arguably the easiest to get your hands on is a common household match. Since the iron (III) oxide in the tip undergoes a chemical reaction as it burns, you get ferromagnetic elemental iron, which easily sticks to a magnet.
Normally ferric oxide is not ferromagnetic. You can see this when you try to stick unburnt matches to your magnet. However, since burning releases carbon monoxide and carbon these reduce the iron to its most basic form. In a larger scale example, you might see a rusted lump of metal that has been in a housefire melt into a non-rusted puddle because of the same reaction.
As a ferromagnetic metal, you could even magnetize those match tips. In an emergency, you might be able to use a burnt match in place of a needle to create a water compass.