There was also a pale clear version which omitted the asphaltum and the cobalt. Before the 20th century, the term asphaltum was also used. Wax, tar and asphaltum have been used since early times. Until the 20th century, the Latinate term "asphaltum" was also used. Following ignition, the heat generated by combustion causes the burning asphaltum to melt and flow. When oil reaches the surface, it is exposed to biodegradation, evaporation, and oxidation, forming asphaltum. Small round shell beads were often set in asphaltum to provide decorations. By the fifth edition in 1685, he had included more asphaltum recipes from other sources.