Essentially, a fossil in the sense of wood turned stone from being submerged under water for centuries. The chemical changes that occur by means of this process bring about its unique structure and deep characteristic colour. The practice of keeping black oak in rivers is in fact a forgotten art, whereby only a few know how to handle this valuable item that was once used to make exclusive furnishings which hold their place in palaces and museums today. Black oak can be found in the Polish river Vistula, Tanew and Odra.