Purification of metals from oil. After the machining or assembly process, mineral and vegetable oils and mineral greases may be present on the metal surface. These impurities come from processing, in which they are used as coolants, or they remain on the metal due to contact with the fitter's greasy hands. Sometimes their presence results from previous heat treatment treatments. Because there is a difference in the nature of different oils and greases in terms of their ease of removal, it is advisable to rank the oils and greases in order from easiest to hardest removed. Vegetable oils are the easiest to remove due to their low viscosity and the ability to react with alkaline components of degreasing baths.. Emulsifying mineral oils, e.g.. E oil can be so easily removed in alkaline baths. Mineral oils are easier to remove from the metal surface, the lower their viscosity, e.g.. the spindle oil is easier to remove than the gear oil, which has a higher viscosity and is applied with a thicker layer difficult to dissolve or emulsify.