Bois Durci is a pulverised wood material based on cellulose. It was patented, in Paris in 1855, by Lepage. It is made from finely ground wood 'flour' mixed with a binder, either egg or blood albumen or gelatine. The wood is probably either ebony or rose wood, giving a black or brown result. The mixture is then dried and ground to a fine powder. The powder is placed in a steel mould and compressed in a powerful hydraulic press whilst being heated by steam. The final product has a highly polished finish imparted by the surface of the steel mould.