In the Upper Middle Ages, in northern Europe, glass was increasingly less raw material and Viking stained glass had to carry out an expensive and expensive process to obtain glass specimens for jewelry and luxury products. Or that's what archaeologists thought so far.

Researchers from the University of Aarhus (Denmark) have studied the chemical composition of these specimens and concluded that they recycled glass. Specifically, they imported treks of Roman mosaics. It was enough to crush the teselas and melt them at low temperature to reuse them, turning the old heritage into medieval heritage.