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I Forge Iron

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I would not know the science of a flame but when I run my coal forge the coal burns at the hottest white and the metal is white hot I will have to look closer tomorrow. also when I keep the fire yellow the heat of the metal is a saturated yellow.
this is out of wikipedia I see no blue on this list.
Temperatures of flames by appearance
The temperature of flames with carbon particles emitting light can be assessed by their color:[10]
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)
Deep: 1,100 °C (2,000 °F)
Clear: 1,200 °C (2,200 °F)
Whitish: 1,300 °C (2,400 °F)
Bright: 1,400 °C (2,600 °F)
Dazzling: 1,500 °C (2,700 °F)

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you didnt mention under what lighting conditions your color chart pertaines to.  Of course how I see color is not the same as how you see color, also very depandant on lighting, so sadly those charts do not mean alot with out a standard referance as a bassline.

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  Well, since wikipedia is on the table, let's look at black-body radiation. Since there is no perfect black-body material, you must take into account the emissivity of the material being observed. This basically means that since coke is a good, but not perfect black-body, the color basically gets applied as a percentage of the black-body radiation chart.  This chart is pretty much a continuation of the chart that you posted here, which accounts for the most efficient flames of oxy/acetylene, natural gas, and the biggest and hottest stars, glowing at various shades of blue. 

  So in theory, if you could get coke to hold out long enough for the entire mass to go up at once, it would glow blue, but since it starts to break down, the little molecules that break off get burnt up very rapidly in the flame that radiates up from the firepot, producing a blue flame.  If it wasn't for the fact that the actual coke was incandescing due to this effect, you would see that the flame in and amongst the fire was actually blue, which is what heats up the coke to the white hot that we see.  Seriously, next time you have a nice clean fire, and a dark background behind your forge, get the coke a nice glowing white hot, kill the blast for a second (so you don't chance forcing forcing non-contributing particles through that will emit their spectral colors, such as phosporus, which emits a pale bluish green color during flame test) and look across the fire.  You will see little blue flames about an inch or 2 tall.  If that's not enough, I don't know what else to say, beyond "I respectfully agree to disagree. Good day, Sir/Mr."

  I wonder what it would take to make iron glow blue.  I bet it would require a perfect non-reactive atmosphere, like argon, and and induction setup with a crucible capable of withstanding about 10000°-20000° F. Good luck with any of that, right? :P

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The game of colours!! If you mean the "BLUE" that is in the tempering range, that is way below what you are talking.


In car paint, to make 'Super White', a little blue is added to white (I was going to say pure White, but there is no such thing).


Colours are a refraction of light to the eyes. What you see as one thing, maybe nobody else see's the same. You can't see tempering colours on a mirror surface, no light bounce.


Aren't we created simple!!!



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I have a further issue, which is true for about 8% of us.  I'm Red/Green color blind, and no, that does not mean that I can't see Canadian comedy shows.  But I see red differently than the run of mill smith.  Especially for heat treating, I use a pyrometer, and ignore the colors entirely.



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  Thomas, I'm not sure which way that one goes, but I wouldn't doubt if there was a plenty of carbon monoxide being produced when the blower is killed.  That doesn't really account though for the fact that the blue flames are still visible when the blower is on, providing plenty of oxygen, or why oxy/acetylene, natural gas, and propane (I got to play with an oxy/propane set-up recently) all burn blue when they're running at perfect flame mixture.  This especially makes sense to me when all of these reactions are based on carbon.

  I'd like to think though that the blue flame while the blower is off is more from very weak (compared to a blower) hot air currents pulling air slowly up through the fire pulling uncombusted hot carbon particles out of the firepot into good oxygen above the fire.  When the blower is on though, you get bigger blue flames, although you might get a few streaks of odd colors from little bits of clinker,ash, non-combustibles, and that little bit of occasional phosphorus/sulfur from unburnt coal dust (you know, the bit hiding in the corner of the firepot on bad days) going through the fire and emitting their spectral colors.  These spectral emissions are why I said kill the blast to get a good look at the blue flames.

  I'm thinking something like the reaction in oxy/acetylene flame.  Acetylene is C2H2.  Combustion with limited Oxygen results in a little bit of water (Hydrogen is very grabby), carbon monoxide(until all left over oxygen is used), and that feathery soot (once there's no oxygen left.)  That's the yellow flame that is really only good for blackening things.  If you add too much oxygen, you end up wasting alot of O2 and probably creating O3 (ozone) from the heat.  It might even kill your flame if you really add too much oxygen to the mix, and take it down below a flammable concentration.  If you add just the right amount of oxygen to the mix though, it is readily available to the acetylene, binds better with the carbon, and you get CO2 and H20.  That's if you have it dialed in perfect, something like 2(C2H2)+5(O2)=4(CO2)+2(H2O).

  I did test one bag of coal from Utah that didn't burn so good though.  Even after it coked (sort of) I was still getting a weak, yellow (sulfur?) flame, that was not the hottest, although I didn't get much clinker for some reason, even when I was wailing on it.

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I thought the "blue flames" on a coal/coke fire showed it was a reducing fire and indicated carbon monoxide was present.

My understanding (much cleared up from a science friday video podcast on fire),  the yellow comes from the incandescence of unburned but hot carbon particles (soot).  Since this is unburned it would seem to me that a yellow flame would create more CO than blue where all the fuel is burning.



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The reason that you can easily get a small focused flame so intensely blue/white that you have to wear tinted specs with oxy/acetylene or oxy/propane/MAPP/propylene, etc. is the injection and mixing of pure oxygen with the fuel.


The vast majority of air is non-reactive nitrogen, and only serves to cool combustion. You need FIVE TIMES the volume of air as opposed to pure oxygen to completely consume all the fuel. This leads to a soft, diffuse flame. Plenty hot enough for soldering, brazing, heating, shaping, etc.

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