Having worked briefly maintaining glass kilns in a number of factories, I would argue over those temps. Typically, in plants producing bottles etc, the temperature mid-kiln would be over 1,000C and in the "fining zone" (the bit just before the molten glass drops into the mould) the temperature would be between 1,200 & 1,400 C. As I used to work on relining the interior of these things, while they were still producing glass, I had to look at those temperatures rather closely. They are hot enough that, when spraying new concrete onto the interior walls (through burner ports), one could work for a maximum of 30 to 35 seconds, followed by a 20 minute rest.