Flame Colors

Flames have many different colors that range from blue to red to orange to yellow. It's even possible to have green flames, although that's not real common in campfires and other small fires that most folks are familiar with.

What can cause flames to be different colors?

One answer is the temperature of the fire: How HOT is it?

The Color of Hot Objects at Different Temperatures

Dark red (first visible glow)500-600°C
Dull red600-800°C
Bright cherry red800-1000°C
Bright yellow1200-1400°C

Wow, that's hot!! Look again at that table. Did you notice that those temperatures are in degrees Celsius (not Fahrenheit)? The coolest temperature in that table is 500°C. Hey, what would that be in degrees Fahrenheit (°F)?
What can cause so much heat to be given off? It really depends on the specific chemical reaction that takes place, which of course depends on the reactants. That's just a fancy way to say "the stuff that reacts with oxygen," or, what burns - our fuel!
Before combustion, the fuel volatilizes, meaning that it becomes a gas, and often decomposes to form smaller molecules, atoms, ions, and/or free radicals. The kinds of smaller species that can form depend on the kind of fuel that we started with. Some simple examples include CH3, CO, H20, and HCN. There are many many examples that are more complicated. For example, when it's hot enough, cellulose can decompose to form molecules that have 5 or 6 carbons, or more.
Once the fuel is a gas, the real combustion occurs, as many (but not all) of these smaller species react with oxygen and produce heat and light: fire!!

O.k., did you notice something weird about the info above? We said "many of these smaller species react with oxygen" because not all do - water won't burn, right? Some flame-resistant or fire-retardant materials are designed to give off water and/or carbon dioxide when they get so hot that they decompose. That way, the water and the carbon dioxide can help to put out the fire, or even keep it from starting in the first place. But, that's a whole 'nuther story (and if you want to read about it right now, you can check out the section on How to keep things from burning in the Topics Menu on the left side of the main page. You can return to the main page by clicking on the home button below.