Simple calculation. (Warning: Math incoming. Non-Asians, brace yourselves!)
Molten ferrous substances have an emissivity of
0.4.
We know the Stefan Boltzmann Law: P = e * o * T^4
where e is emissivity, o is the boltzmann constant, and T is the temperature in kelvin. A perfect blackbody would thus have
P1 = 1 * o * T^4
Now we calculate, if we assume it's iron, according to the visual identification it looks like it's at least 1300°C (1573K) hot at its hottest when it's visible.
P2 = 0.4 * o * (1573K)^4
Now for another material to appear as bright as iron, we can assume that in the worst case it's a perfect blackbody that doesn't occur in nature. P1 = P2, x is the temperature of the perfect blackbody:
0.4 * o * (1573K)^4 = o * x^4
We resolve for x
0.4 * (1573K)^4 = x^4
(0.4 * (1573K)^4)^1/4 = x
0.4^1/4 * 1573K = x
1573K / 2.5 = x
1250K = x
That means the lowest possible temperature of the item in question, that is, if it's in fact a perfect blackbody that doesn't occur in nature, is 1250K = 975°C = 1790°F
Add in a margin of error, and it still can't be cooler than 900°C - after it lost already hundreds of kelvin flowing to the edge of the building from the core (edge of core to edge of building = ~80-90ft)
Meaning, even if you assume this is pixie dust, you still have to wonder how or why it got so hot, if the fire in the WTC didn't even manage to heat the glass windows to the point where they blow out which happens at 700°C...
EMH, you're still just protesting the evidence. Come up with an alternative explanation.
I can explain everything to you with just one word: "Thermate"
And that means it's the best theory to explain the observation.