It’s easy to make red flames or red fire. The colored fire is a practical application of the flame test in chemistry.
Ingredients for Red Flames
All you need is a suitable metal salt and a fuel:
- Strontium or lithium salt
- Clean-burning fuel
Strontium and lithium salts produce red flames. Strontium, in the form of strontium nitrate or strontium chloride, yields the red color seen in emergency flares and red fireworks. Lithium chloride produces a vivid reddish-violet or pink flame.
A strontium salt is your best choice because it’s readily available and not toxic. It is a mild irritant, so if you handle it, gloves are advisable. The red color is bright enough you’ll even see it in a regular wood-burning fire.
Lithium chloride is readily available online. You can find tutorials for extracting the metal from batteries or greases, which also burns with the characteristic pink color.
For best results, you need a fuel that burns with a blue or nearly invisible flame. Here are some good choices:
- Methanol
- Ethanol
- Rubbing alcohol (isopropyl alcohol)
- Lighter fluid
- Hand sanitizer
- Natural gas
- Propane
Make Red Flames
Once you have the materials, making red fire is easy. Simply sprinkle the chemical onto the fuel and ignite it. All of these fuels are highly flammable, so use a long-handled lighter.
Getting Strontium From a Flare
One advantage of strontium is that it’s often available from stores, if you know where to look. You want an emergency flare. It needs to be the cardboard kind you strike on a rough surface and not the electronic kind.
Peel away the cardboard of the flare and collect the powdery chemical inside of it. Store the powder in a sealed container for use in projects, since you only need a small amount at any given time.
Other Red Flame Colorants
Now, lithium and strontium salts are not the only chemicals that make red flames. They are the easiest chemicals you can find with low toxicity. Here are other metal salts that work, along with notes about color and safety:
- Rubidium (reddish violet)
- Zirconium (pale red)
- Calcium (sometimes brick red, but also orange or yellow, depending on the compound)
- Cadmium (brick red, toxic)
- Mercury (red, highly toxic)
- Yttrium (crimson, not readily available)
- Radium (crimson, highly radioactive)
Of these elements, rubidium is the one that is easiest to find online. It is often used in chemistry demonstrations. Rubidium is an alkali metal, so it is highly reactive in pure form. It’s stored under oil or in an inert atmosphere because it reacts vigorously with water. If you want red flames using rubidium, order rubidium chloride online. Rubidium chloride displays low toxicity and is safe to use.
Hydrogen sometimes burns with a reddish-orange flame. The usual emission color of a hydrogen flame is faint blue. However, burning hydrogen sometimes appears red. For example, a Delta IV rocket burns hydrogen and has a reddish flame just prior to take-off. While it’s unclear exactly why hydrogen has different emission colors, it’s likely due to an interaction with other elements and compounds. Also, the H-α emission line of hydrogen is red.
How Red Flames Work
The red color comes from the emission spectra of elements and compounds. Typically, metal ions produce the vivid colors we associate with fireworks and colored fire. The heat of the fire gives the electrons in the atoms or ions enough energy that they jump to an excited state. Electrons return to a less-excited state or ground state, releasing the excess energy as photons (light) with a characteristic wavelength. Substances that make red flames predominantly emit photons in the 620 to 750 nm range.
Incandescence also affects flame colors. This is the glow associated with flame temperature. Unfortunately, red incandescence is not very visible. Such a cool flame tends not to release much light, plus the human eye does not perceive red as readily as orange and yellow. Any sodium in the air or fuel overpowers red with a bright yellow color.
Projects Using Red Flames
Here are projects using red flames:
- Light a Halloween jack-o-lantern using red flames.
- Make a tabletop fire tornado with red and blue flames.
- Make colored fire pinecones.
References
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. ISBN 1439855110.
- Landis, Arthur M.; Davies, Malonne I.; Landis, Linda; Thomas, Nicholas C. (2009). “‘Magic Eraser’ Flame Tests”. Journal of Chemical Education. 86 (5): 577. doi:10.1021/ed086p577
- Melvill, Thomas (1756). “Observations on light and colours”. Essays and Observations, Physical and Literary. Read Before a Society in Edinburgh. 2: 12–90.
- Sanger, Michael J.; Phelps, Amy J.; Banks, Catherine (2004). “Simple Flame Test Techniques Using Cotton Swabs”. Journal of Chemical Education. 81 (7): 969. doi:10.1021/ed081p969
- Pan, M.; Xiao, W.; Albadi, A.; Han, Y. P.; Zhang, Y. (2019). “Further Investigation of Hydrogen Flame Colour“. 27th ICDERS. Beijing, China.
- Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.