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.)|
|yellow||sodium chloride (et al.)|
|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.
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.)
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.
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.
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.
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.