Ron,
The slag is the colored plastic wrap that surrounds a 6 pack of Lipton iced tea. It works well because an LED light behind it lights the whole length of the plastic wrap, and is especially dramatic when the room lights are lowered. When I first tried to just use an orange or yellow plastic bag, the light just looked like a smudge from the front. In addition, the colored plastic wrap has vertical parallel ripples from where it bends around the edges of the bottles so that it has a depth to make it look 3 dimensional when it is being poured out of the slag car or from the blast furnace floor into a hot metal car.
Doug
