What Color Is the Hottest Flame and What Do Different Colors Mean?

Most people think of a traditional orange fire when they think of flames. But there are many situations where fire doesn’t burn orange. In fact, flames can be every colour in the rainbow. So, why do flames have different colours? What kinds of chemicals can make fire change colour? How does the temperature affect things? All of that and more will be brought to light.

How do different colours of flames come about?

To figure out what makes flames of different colours, you need to understand how visible light and fire work. First of all, fire is a chemical reaction that happens when chemical and gas molecules interact with oxygen and cause combustion. Also, not all fire is on the scale of visible light.

Visible light is any type of electromagnetic radiation that can be seen with the naked eye. When light goes through a prism, it changes into the colours we know. We can see different colours because their wavelengths are different. For instance, the wavelength of red is the longest and the wavelength of violet is the shortest.

When flames change colours, it’s because they’re reacting to heat and chemicals. The range of fire’s normal colour spectrum, from cool to very hot, is represented by the acronym ROYGBIV, which stands for the colours red, orange, yellow, green, blue, and violet.

Red

Orange

Yellow

Green

Blue

Indigo

Violet

Which colour shows the fire that is the hottest?

Even though it looks cold, violet is the colour of flame that is the hottest. Violet flames are so hot (over 1,650 degrees Celsius) that they can easily cut through almost any metal, glass, or rock. Because of this, welding torches often have violet and blue flames at the end. Even so, welders wear goggles to keep their eyes from getting burned by the light.

It’s also important to know that the carbon and hydrogen in burning wood can also make violet and blue flames. This is why, when you’re sitting around a campfire, you might see blue or violet flickers.

Violet flames can burn through even the toughest materials, but red flames, which are the coolest, are not as strong. Even though red is a colour that is often associated with fire, it is not the hottest flame. Its temperature stays between 600 and 800 degrees Celsius. This might sound like a high temperature, but compared to the blue flames, which are 1650 degrees, this is a pretty low temperature. Still, flames this hot can melt aluminium, pure silver, tin, lead, bronze, and brass. Fun fact: Some red flames are so cool that you can’t see them with your naked eye, but flames that get to 800 degrees will burn a rosy red colour.

As you can see, there is a clear connection between how hot a flame is and what colour it burns. Flames that aren’t as hot or are starting to go out will look different than flames that are really hot or just started. The colour of the flames shows how much heat and energy are given off when something burns. To sum up, the violet flame is the hottest on the colour spectrum, and the white flame is the hottest on the visible spectrum.

Here’s a more complete list of what each colour of flame can burn and at what temperature:

Flames that are red burn at about 600 to 800 degrees Celsius. The hottest of red flames can melt substances such as magnesium (657° C), glass (700° C), and borax (740° C), while the coolest of these flames can melt lithium (179° C), selenium (220° C), tin (232° C), amber (300° C), and zinc (419° C).

About 1100 degrees Celsius is the temperature of a flame that is orange. These flames can scorch through bronze (910° C), gold (1063° C), and copper (1083° C).

Yellow flames burn at approximately 1200 degrees Celsius. These flames will melt arsenic (815° C), calcium (850° C), brass (900° C), silver (960° C), and radium (960° C).

Interestingly, green flames have no link to temperature, but rather to the chemicals that fuel them, which we will discuss below.

Blue flames burn at approximately 1400 to 1650 degrees Celsius. This makes the coolest blue flames capable of melting asbestos (1300° C), steel (1460° C), and cobalt (1490° C), and the hottest blue flames capable of melting palladium (1552° C), brown iron ore (1570° C), melting clay (160°0 C), and agate (1600° C).

Indigo flames burn at just under 1650 degrees. These flames can melt through aluminum bronze (1040° C), quartz (1470° C), iron-oxide (1570° C), and sand (1550° C).

White flames burn at approximately 1300 to 1500 degrees Celsius. These flames can burn through many tough solids, including uranium (1133° C), nickel (1452° C), and cobalt (1490° C).

Violet flames burn over 1650 degrees. This makes these flames powerful enough to turn hard-to-melt materials into puddles, such as cast iron/forged iron (1200° C), steel (1460° C), porcelain (1650° C), and titanium (1670° C).

What Chemicals Change the Color of Flames?

Temperature isn’t the sole determiner of the color of flames. Different colors of flames can also stem from the types of chemicals that are present in the substance that’s being burned. The type of fuel and its impurities, in addition to the flame temperature, contribute to the color of the flame.

Certain chemicals in wood, candles, or other fuel sources can spark varying colored flames at their source. That is, elemental particles the flame’s illuminating influence its color as much as the temperature the fire burns at. These are the chemicals and materials responsible for fire’s various colors:

Red: Caused by strontium chloride or strontium nitrate. Spotted in slow-burning fires.

Orange: Caused by the burning of carbon particles or calcium chloride. Spotted in most campfires, charcoal grills and fireplaces.

Yellow: Caused by sodium chloride, sodium carbonate, or borax.

Green: Caused by copper or barium. No link to temperature.

Blue: Caused by copper chloride or the complete burning of carbon in a fuel source.

Indigo: Caused by indium.

White: Caused by magnesium sulfate.

Violet: Caused by potassium nitrate mixed with potassium sulfate.

Why Are Orange Flames the Most Common?

When it comes to fire, why are orange flames the most (seemingly) common color? Orange flames run at approximately 1100 degrees Celsius, putting them in the middle range of flame temperatures. Most organic items that people burn — paper, wood, charcoal — contain carbon. So, when these items are burned, they release carbon particles into the flame, causing these particles to create deep orange, “clear” orange, and yellow flames.

When all carbon particles are burned out of a fuel source — and there are no remaining traces to be consumed — the flame may then spark blue or violet in response. For example, stovetops and gas grills both feature blue flames because they’re not responding to a carbon-based fuel source.