It is here in the FS furnace that the raw ore concentrate is smelted into matte copper having a 68% to 70% copper content. Periodically the furnace reaction is shut down long enough for inspection ports on both the FS and the FC furnaces to be opened and the interior of the furnace visually inspected. Before opening the ports the slag level in the furnace is typically drained to a level below the tapping ports, this makes starting the reaction again easier and more efficient. The 2 small dark triangular areas are 2 of the 3 slag tapping ports as seen from the inside of the furnace. When the inspection ports are opened cooler air is drawn in causing the bath to scale over and take on the dull orange color seen here, the white hot areas are portions of the bath under high intensity natural gas manage burners used to maintain interior heat levels during the inspection as well as helping control interior build up of solid material. The area inside the furnace is roughly twice that of the FC. When the inspection doors are closed and sealed again and the reaction started the entire bath becomes a molten bright yellow/white hot color reaching temperatures of nearly 2400 degrees. This image has been artistically rendered to enhance detail and contrast.