A second alarm brought a total of 30 firefighters to the scene.
Investigators say the blaze began in a vat used to melt glass. The flames spread to the point where they were threatening the plant.
Firefighters flooded the molten glass with water and brought the fire under control after about an hour.
There's no immediate word on the cost of repairing the damage.
Previous fires hit the plant on March 10th and again on May 25th. Fire officials say there have been seven fires at the plant since 1996.