Answer:
The method of processing bitumen was nearly universal: heat it until the gasses condense and it melts, then add tempering materials to tweak the recipe to the proper consistency. Adding minerals such as ochre makes bitumen thicker; grasses and other vegetable matter add stability; waxy/oily elements such as pine resin or beeswax make it more viscous. Processed bitumen was more expensive as a trade item than unprocessed, because of the cost of the fuel consumption.
Explanation:
