The color of fire

[Francis Trez Cole]

The color of flames
Ok the question was asked to me by a young man what is the hottest fire. He was referring to forging in the production of a sword. Well his response to me was blue. After some talking to the guy I found out that he had learned the information from a video game. I told him he needed to get out in the real world for a learning experience. In blacksmithing the hottest fire was white. Doing some research this is what I found on the internet.
A flame is a mixture of reacting gases and solids emitting visible, infrared, and sometimes ultraviolet light, the frequency spectrum of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.
The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.
• Typical temperatures of fires and flames of a chemical nature
• Oxyhydrogen flame: 2000 °C or above (3600 °F)
• Bunsen burner flame: 1,300 to 1,600 °C (2,400 to 2,900 °F)
• Blowtorch flame: 1,300 °C (2,400 °F)
• Candle flame: 1,000 °C (1,800 °F)
The temperature of flames with carbon particles emitting light can be assessed by their color that is the burning of wood, charcoal, coal and coke.
• Red Just visible: 525 °C (980 °F)
• Dull: 700 °C (1,300 °F)
• Cherry, dull: 800 °C (1,500 °F
• )Cherry, full: 900 °C (1,700 °F)
• Cherry, clear: 1,000 °C (1,800 °F)
• OrangeDeep: 1,100 °C (2,000 °F
• Clear: 1,200 °C (2,200 °F)
• White
• Whitish: 1,300 °C (2,400 °F
• Bright: 1,400 °C (2,600 °F)
• Dazzling: 1,500 °C (2,700 °F)

Oxyhydrogen may produce the hottest flame but I seriously doubt any of us will be setting up a forge to use Oxyhydrogen as a fuel source.

[Jim Coke]

Greetings Francis, 

 

Thank you for the interesting info... I will copy it  and post it in my shop..  Its easier to point to a chart than answer all the questions we normally get..

 

Forge on and make beautiful things

Jim

[yahoo2]

 

source http://www.fluidynenz.250x.com/May09b/calandies.html

 

this photo is a filtered and dried wood gas flame taken at night (not visible in daylight due to light pollution) the gain in energy produced from removing the large chain molecules, water and fine particles that absorb energy from the reactions is massive.

 

The flame may be blue and technically hot but there is not a lot of intensity here due to the large area that the flame front needs to mix with air to burn (compared to an oxy/acetylene flame that is clearly visible in daylight and fed pressurized oxygen) and there is almost no radiant heat like you get in a cooler but more intense fire like a forced induction burner or forge.

[ianinsa]

Hi Francis, not wishing to differ but... as I understand it  both oxy/acetylene and oxy-petrol(gasoline) burn at way over 2000c in fact closer to 3000c with a blue flame....?

 

Ian

[ianinsa]

A further thought, I have an old Arcair slice system that ''burns copper covered carbon'' in an exothermic system (I don't fully understand the process )(spark it up and Voodoo happens :D ) a frightening system and I am led to believe this creates over 5000 degrees C (I don't know for sure, but I have a Pac 90(big )plasma and oxy/acetylene and they don't even come close.

 

Ian

[Marksnagel]

This is a picture of the wood gas in my charcoal retort burning. Don't know the temp but it is white hot.

 

[ianinsa]

Mark, that retort is ''smoking hot'' ha, ha!  You know that Arcair burns through refractory like a blowtorch through polystyrene!

 

Ian

[EricJergensen]

Incandescence is always the same color regardless of the material: iron, copper, soot particles, etc. That's why Francis Trez Cole's chart above about fire temperature (i.e. incandescent soot particles) looks very familiar.

 

That's also why a coal fire with gentle air blast is a decent reference color for welding heat. It's a 2200°F-ish flame and when the incandescent steel is the same temperature as the incandescent soot it's exactly the same color.

[Stefflus]

Yup, the point here should be to separate the snot from the mustaches (Norw. proverb), or the soot from the flame, so to speak.

I don't think I've ever seen a flame that was anything other than blue unless it was polluted by soot or the flame was hot enough to ionize particles (like with borax in a forge, or the chemical flame color test).

CO gas burns blue, Hydrogen burns blue, Sulphur, ethanol, the purified wood gas in the picture above, small flames on candles and matchsticks etc..

An entirely different matter is luminousity, which could make a blue flame look white to the human eye.

[Borntoolate]

So let's make this simpler for those that have simple things.   Take a box store bought propane torch.    The flame has several visible colors and a very distinct flame pattern.    

 

If you are using a simple torch like this, as many folks will... what part of the flame and what color is the hottest?  

 

Maybe even slightly more complicated let me ask how you would use such a torch to impart the most heat to a given object?

[Rich Hale]

Applying this chart to shop settings may confuse new folks...Ambient light is a huge determining factor in the color we see ,,a certain color of flame or metal in dim light will change dramatically in bright sun. many new folks forge outdoors or in shopw with large doors to outside light. dark or bright...Eric hit a big point above when he mentioned the color of the steel reaches the color of inside of forge...I weld at that temp ,,either in shade or sunshine with a gasser... my coal forge is outside and the light is different than inside a gasser,,,

[yahoo2]

With a propane torch or oxy/propane with a neutral flame the inner cone is colder than the second luminous cone is the hottest area and the third blue area is the leftover gas mixing with the surrounding air and burning. One of the mistakes i made when I first used a Oxy propane cutting torch after learning with an acetylene rig was holding the torch too close while I was preheating the cut, the inner cone is a bit larger due to the slower burn rate of propane so I was trying to heat with the cooler part of the flame.

 

The blue colour is ionisation so it is not the same thing as blue (seriously hot) from black body radiation.

 

Nor is it the same blue as the bright blue or violet in a nuclear reactor pool called the Cherenkov effect, which is totally unnerving.

[ianinsa]

'' black body radiation''.............KE......???????  wotsat??????? Huh! :D

[John McPherson]

Black body radiation is how you measure heat and light emission. The opposite would be a perfect mirror. Chrome is the worst offender in overheating parts in show cars, stove black makes a wood stove more efficient in heating a space.

 

http://en.wikipedia.org/wiki/Black_body_radiator