Today's flat glass production is subject to very strict quality demands. Statutory prescriptions as for maximum recycling quota, and minimum use of primary raw materials and energy. Recycling cullet is a way to do so, but not everything can be recycled. Two examples, mirror recycling and recycling of glass from scrap cars, show that it is only possible to recycle external cullet into a float glass furnace if and when it is of premium quality. Low amounts of known contamination are often tolerable. Because of the complexity of glass recycling from diffuse sources, such cullet is often expensive and a considerable residual risk of contamination remains. As potential damage for flat glass production is still high, still today most producers refuse its use.
