This is the second picture selected from the set I took at the fireworks in my city a few days ago. I believe that the first one, Dandelion forged in strontium, was a little bit more impressive (without being marvelous) but this one is also pretty in a minimalistic way. The composition in this one is shifted to the left. Instead of showing the part of the funfair on the horizon, this time I chose to show the buildings in the city. They are dark and blurry (thanks, wind!) but at least they are visible enough to provide a context: A synthetic flower over a forest of concrete buildings.
As I promised a couple of days ago, I’m going to talk about firework’s colors.
Matter is composed of atoms, that are linked together to form the compounds that conform everything around us. There are very few kinds of atoms, 118 discovered until now, but only 78 are abundant enough to be used in everyday processes (I don’t include uranium, plutonium and other radioactive elements which are unstable and created just for their consumption in very specialized industries). What makes matter different is not only the kind of atoms they are made of, but also the number of each it has and how they are linked together, in the same sense as Lego pieces form bigger figures. Those atoms are composed by a core made of protons and neutrons, and a “shield” made of electrons. And those electrons are the magic of the color in the fireworks (in fact, they are the magic of almost everything, but now I’m talking about fireworks).
The electrons of an atom are characterized by their energy. When they are left alone, they have the minimum possible energy to be linked to whatever they have around. But it might happen that, when you provide them with more energy, they will accept it. This increase of energy will be retained by them for a short period of time (usually the time is less than 1 nanosecond) and afterwards they will release it again. The most typical way of providing them with energy is by heating (for example, with a flame), and releasing the energy as heat is also very common. But also some of the energy is released as light, and depending on the amount of energy the color of the light will be different. This amount on energy that an electron can gain and lose is characteristic of every type of atom, and it is useful for identifying them (for example, in a mixture).
A firework is composed mostly of gunpowder, which works as a propellant so it can fly, and a shell, that also includes gunpowder to make it explode. And the explosion provides a lot of energy that any present atom can use to transform it into colored light. Many of the atoms provide light in energies that cannot be seen by the eye, but a few of them provide colored light, and those are the most useful when making fireworks:
- Barium: Barium emits mostly green light when excited, so any firework that contain barium will be green. Usually it is not a very catchy green, so it is usually used combined with other salts to increase its appeal and tune the color (make it a yellowish green or a bluish green). Barium is also what they make you eat when they want to take X Ray from your bowel. Bowel tissue is transparent to X rays, so they won’t see anything (like taking a picture to the glass of a window), but barium is opaque. Filling the bowel with barium is like staining the glass with dark powder so you can see any fissures it might have, and reveals the shape of the tissue.
- Sodium: Sodium salts, like sodium chloride (table salt) provide a yellow-gold hue. Sometimes it is used combined with other salts to modify their color a little bit. Sodium can be found in our bodies, and is one of the elements that sustain our electrical system (nerves, but also charge potential useful in our cells).
- Calcium: Calcium salts provide a very deep and intense orange, like in orange juice. Calcium salts are famous for being good for your bones but they are also used in construction, toothpastes and optical glasses. Calcium is a very versatile element!
- Lithium: Lithium provides a very intense oragish-red color, very attractive to the eye. It is used to provide red color in the main parts of the firework. Lithium is also used in some medicines for mental diseases, as it connects well with the brain chemistry.
- Strontium: Similar to lithium, it provides a red color. But in this case this red is less brilliant and deeper in hue. It works well to provide a red color to accessory parts of the firework. It was extensively used a few years ago to build the screens of color television’s cathodic tubes and other similar screens.
- Copper: Copper provides blue light when is excited. It can be used on its own, to provide a cyan color, but also combined with strontium to create purple hues. Copper is a very versatile metal apart from fireworks, and has many uses pure (wires, pipes…) and as an alloy (brass, bronze).
- Cesium: Cesium creates indigo light when excited. It is not very used as it is relatively expensive and you can achieve the color with some mixtures of other salts, but if you require the exact hue, then it is used. The most known use of cesium apart of fireworks is to make atomic clocks measure time.
- Magnesium: Magnesium provide white light, but extremely intense. It can be used on its own to create white light but also combined to any of the other elements to slightly increase their intensity. Magnesium is used as a metal to create alloys that are highly resistant without increasing their weight (aeronautics), but also as a salt in many ways: optic glasses, paper industry, fireproof woods…
Also, some other metals are combined to those above to provide special effects. Those are some of them:
- Aluminum: Aluminum can be used to create bright sparkles that burst out of the explosion. The brightness is a property of the metal, while the way the sparkles happen can be controlled with the shape of the aluminum particles.
- Antimony: Antimony creates a glitter effect, as it reflects the light in a very characteristic pattern. Apart of alloys, it is mainly used as a fire retardant.
- Iron: Iron particles can change their color when temperature varies. They are used to create long lasting particles that change from bright yellow to dark red with time.
- Zinc: Zinc is not colored by itself, but it is used to create smoke effects. The small particles of smoke can reflect the light of other compounds in a diffuse way.
- Phosphorus: It works in a similar way to “glow in the dark” stickers or figures. The difference with the previous elements is that it can retain the energy for longer periods of time (sometimes over 1 second, which means 1000 million times longer). The color is usually yellowish-green, but it is used for effect that last for many seconds.
If you think this a matter of magic and not an everyday issue, think again! When you light a propane or butane cooker, the flame is blue. Those gases are mainly composed of carbon, and carbon emits blue light when is excited with heat (and a butane flame is very hot, more than 400 ºC). Have you ever tried to boil something and the water spilled over the flame? If you remember, when this happens, the flame turns yellow. This is due to the amounts of sodium chloride the water have (especially if you added salt to it).
Do you want to try it yourself? Use a little flame, like the one in your cooker or a candle (warning, this is hot and you know it, be careful if you try) to burn small amounts of different salts solutions. You can take a rigid wire and make a tiny “O” on one extreme (like the device you use to make soap bubbles, but in a smaller scale), then take a little bit of liquid with it and put it over the flame. The flame will change the color for a moment depending on the salt used. If you use table salt, you are using sodium. If you use low sodium salt, you will be using potassium (reddish color). Do you want to use copper? Add a small amount of vinegar to the water and leave a piece of copper for a few minutes, until the solutions starts to turn green/blue. You can try that solution. And remember, you don’t need a high amount of the salts for this to work.
So, after this long explanation, next time you see a good fireworks show take a second to think about all the elements, compounds and knowledge that is needed to make them.
Can you identify the elements in the last two published pictures?
Javier Torres. Photography 