How to: make Colored Flames

The concept

You can use a methanol flame and various ionic substances (salts) to make colored flames. All of the flames pictured in this post were produced by me using the methods detailed herein. Most of the substances mentioned below can be obtained inexpensively from ordinary merchants (i.e. no need to visit a chemist).

green boric acid (et al.)
lavender potassium chloride
yellow sodium chloride (et al.)
orange calcium chloride
red strontium chloride (et al.)

You only need between one and 3 mL of methanol for a non-overlarge flame to burn for a couple of minutes. See the snapshot of the vials and pen for an idea of scale.

Where to get methanol

The only easy means I found for getting small amounts of methanol is buying gas-line anti-freeze. HEET antifreeze can be found at 7-11, AutoZone, O’Reilly Auto Parts, etc. for about $3/bottle. It’s 99% methanol.

Green flames

For a few dollars, you can get a big box of boric acid at the grocery store, under its commercial name: Borax. Find it with the cleaning supplies. The green flame pictured at the top of this post was produced with Borax. It dissolves/suspends easily in methanol.

The problem with the boric acid flame is that when the flame gets very hot, it turns yellow. If you burn your methanol in a container that conducts the heat away, or if you only use a little bit of methanol (so that the flame does not continue too long), this may not be an issue for you.

Copper salts, such as cupric chloride, a.k.a. copper II chloride, produce a richer color, and when the flame gets hot, it migrates from green to blue. A cheaper alternative to cupric chloride is copper sulfate, which I found for five dollars a pound at the local feed and supply store (it’s used as an herbicide and an algaecide); however, although copper sulfate is used as a blue pigment in pyrotechnics, I was not able to get a colored flame from it in methanol. (Perhaps a future post will describe how this and other substances can be used in standard pyrotechnics to produce deeper colors.)

Lavender flames

Potassium is what gives us the lavender flame. You can find potassium chloride in your grocery store, sold as a salt substitute. Check the spice aisle.

You can see from the pictures that I got some nice color from the substance, but be warned that I could not get it to dissolve or suspend at all in methanol. Dissolving it in water and putting about one part of the water solution to six parts methanol gave me a bit of effect, but what was most effective was to also pour a pile of the potassium chloride into a container, cover it with methanol, and wait until the flame got quite as hot as it would.

Yellow flames

The two yellow photographs in this post suggest that I got a really rich yellow or orange flame, but in fact to my eyes, the flames seemed far less intense, not so different from a candle flame. I suppose that the camera’s vision was not true.

Sodium gives us the yellow color, and you can use table salt (sodium chloride) or baking soda (sodium bicarbonate), either of which can be obtained from the grocery store.

I found this substance much like potassium chloride in that it would hardly dissolve or suspend. Again, I recommend packaging the salt and alcohol separately, then pouring one over the other when it’s time to touch it off.

Orange flames

Calcium chloride, which a friend on staff at the local community college supplied me, provides a nice orange flame. This was probably a bad example to use because 1) I don’t know how to obtain it commercially, and 2) it is so hygroscopic that I don’t know how to work with it easily — in other words, if you leave the lid off of it, it will suck water from the air until you have a puddle of dissolved calcium chloride in your bottle. And I don’t even live in a very humid area.

Red flames

Strontium and lithium are used for red pigments. For about $3.50, you can get a tub of strontium carbonate (see previous post); lithium is about six times as expensive.

The red flame pictured above was produced with strontium, but strontium carbonate actually wouldn’t give me any color in methanol. I added muriatic acid (available at pool supply stores) to the strontium carbonate to produce strontium chloride, which is what I used in the flame. (Instructions on how to make strontium chloride appear in the previous post.)

Strontium chloride dissolves/suspends pretty well in methanol. When the flame is cool, you get a nice magenta color; when the flame gets hot, you get red/red-orange.

Tips & tricks

Use methanol because it has an invisible flame, which will allow us to see the colors emitted by the salts. — Other flammable substances, like ethanol or naptha, produce enough white light that adding any color to it will not yield an observable result.

Your salt pigments are not actually going through a chemical reaction. That means that they don’t get consumed, and you can recover them (or just pour more methanol on them) and use them again.

Because methanol is so apolar, it will not dissolve your salts as well as water would. It is necessary in some cases (mentioned below) to add water to your mixture and/or pour ethanol over a small pile of undissolved salt.

These chemical-to-color listings may differ from others you’ve seen

You can find long lists of chemicals and the colors they produce in pyrotechnics or flame tests. In both pyrotechnics and flame tests, your chemicals absorb more heat than our methanol flames will produce. Consequently, you read here that cupric chloride produces a green flame, but other sites will tell you it is a blue pigment.

You can achieve richer colors with higher temperatures, but for the treasure hunt for which my flames were intended, I preferred to avoid high temperatures and the copious amounts of smoke that accompany standard pyrotechnics. The small alcohol flames discussed here are safe for indoor use.

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4 Responses to How to: make Colored Flames

  1. Celine To says:

    My friend and I are doing colorful fire for our science fair project this year, this post was really helpful! We’re having a hard time find out WHY it turns to the certain color. Can you tell us why it happens?

    • Markham says:

      The ions (the individual atoms of the dissolved salts) absorb energy from the heat of the fire. This energy is used to escalate the ions’ electrons to unnaturally high orbital levels. These unnatural orbitals are unstable positions for the electrons (due to the nature of the elements concerned and the number of electrons they hold); consequently, the electrons do not remain in their higher orbitals but “fall” down.

      As energy was used to elevate the electrons to a higher orbital, that energy is released when the electrons drop to a lower orbital. It happens in the case of these chemicals that that energy release takes place in the form of photons. A photon’s colour is due to the length of its wave, which corresponds to how much energy it holds. (The farther the fall, the more energy released, the longer the wavelength. A short fall could produce red; a higher fall could produce blue.)

  2. Corey872 says:

    Calcium chloride is sometimes available as an ice melting salt used for sidewalks/driveways, etc. Look for ‘super ice melter’ or ‘hot stuff’ or ‘all natural’ – and double check the label. Generally the ‘specialty’ ice melters in the fancy jug or box are calcium chloride. If it’s a plain 50# bag, it’s likely sodium chloride.

  3. Bruno says:

    Borax is NOT boric acid. It is a boron salt that could be obtained with boric acid though.

    Borax’s chemical formula is Na2B4O7 and boric acid is H3BO3

    Chemical structures are totally different, yet both would work in getting a green flame since the important part is that you actually burn boron. Boric acid can usually be found in drugstores as an antiseptic.

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