metalresearcher - 22-10-2013 at 11:27
Welding (or arc melting) of steel results in a nice blue arc light which is actually the spectral color of iron, as yellow the color of sodium is.
Why are iron salts not used in fireworks ? Are they too unstable or not volatile enough?
I tried mixing KClO3 and sugar with a bit of CaCl2 which results in a nice red flame. Unfortunately I have no FeCl2, otherwise I tried that when it
is now too hygroscopic.
Any ideas on this?
Praxichys - 22-10-2013 at 11:40
Are you sure? I think the blue is just from the short wavelength blackbody electromagnetic radiation from the hot material in the arc.
Tig welding of aluminum under a blanket of helium produces the same color, and no iron should be present in that instance.
Empirically, sticking a bit of steel wool into a hot flame produces no blue coloration.
http://chemed.chem.purdue.edu/demos/main_pages/6.2.html
[Edited on 22-10-2013 by Praxichys]
blogfast25 - 22-10-2013 at 11:51
According to this source:
http://student.fizika.org/~nnctc/spectra.htm
... the emission spectrum of Fe has many lines in the blue and some in the green.
The reason why iron isn't used as a pyro colourant may lie in the relative intensities of the emission lines, making some elements more suitable than
others.
Wizzard - 22-10-2013 at 13:13
Aluminum burns blue in atmosphere, when heated properly 
Take a ribbon, and burn
it quickly with a hot torch - Bright like magnesium, but blue! I've never seen iron burn blue, however.
phlogiston - 22-10-2013 at 14:12
At lower power levels, some of the emissions of electric sparks do come from the ionized metal gas.
Just play a bit with a modest cap (say a few 1000 uF at 10-20 volts or so), and different metals for electrodes.
Copper gives a distinct green. Aluminum and iron both give blue, but somewhat different tinges.
high-carbon iron yields the characteristic branching sparks.
In an arc-welding situation, however, I also would expect black-body radiation to overwhelm any iron emissions.
In fireworks, the intensity of the emission, the volatility of the relevant species, the chemistry in the flame all come into play. Blue colors in
todays fireworks are most commonly obtained from CuCl<sup>+</sup>, which is formed in a flame containing copper and chlorine species if
the conditions are exactly right. A pure and bright blue is actually notoriously difficult to make.
[Edited on 22-10-2013 by phlogiston]
Trotsky - 25-10-2013 at 22:31
Is it related to the argon used perhaps?
vulture - 26-10-2013 at 04:34
It's not the iron, it's ionized air (or gas):
http://en.wikipedia.org/wiki/Ionized-air_glow