During the Industrial Revolution coal became the main source of coal energy making possible the rapid mechanization of industry. Today it represents the third source of energy after oil and natural gas, above all because it is a highly polluting fuel. Coke is the raw material for steel production. The steel and metal industry uses coke: it is a solid and hard fuel obtained by heating the coal at high temperature. Coke is the raw material to produce steel. Other industrial processes use coal gases to produce fertilisers, pharmaceuticals, pesticides, etc. Tar is also obtained from coal through distillation. The natural dislike of its colour and smell did not prevent the chemistry experts of the 1700s from discovering its virtues: wood painted with tar becomes waterproof and resilient against microbes. Moreover, in developing countries coal is still used for household tasks: heating and food cooking.