Looking into an electric arc furnace with the power on

What you’re seeing here is the arc between the tip of an electrode and liquid steel, which is hidden under nearly a foot of slag (the bubbling liquid you see here). This video was recorded entirely by chance, I was videoing other things when I realised that I had a clear view of ’A’-phase. I had to use two crossed polarised filters in order to block out enough light to see things clearly - and yet the arc itself is still blue-white and indistinguishable!