Put the sword into the furnace

From Reddit Choose Your Own Adventure

You open the furnace door, and slide the blade in careful not to knock any of the clay off. You pump the billows, and the temperature rises.

Do you:

• heat the blade up to 760ºF
• heat the blade up to 860ºC
• heat the blade up to 860ºF
• heat the blade up to 760ºC