Grease is a complex mixture consisting of fats, waxes, pigments, protein acids and glycerol. If the composition of fats (fats of fish and marine animals) and oils (linseed, soybean, sunflower, hemp, cotton) are dominated by unsaturated fatty acids capable of polymerization reaction, with long-term contact with the tissues they form insoluble films.
Such grease stains to remove from carpets and upholstered furniture is pretty hard. If the composition of the fat is dominated by saturated fatty acids, in contact with the fabric of the garment they do not polymerize. For example, such fats and oils include beef, pork and mutton fat, butter, castor, palm oil, etc.
These types of fats and oils can be removed with detergents, it is necessary to be careful, as fabric of the sofa can lose color.
Vegetable oils consist mostly of unsaturated fatty acids. During aging cooking oil stains, especially on light and at elevated temperatures, not only formed a solid polymeric molecules, but also due to the double bonds in the interaction of fat molecules with the polymer molecules of the fabric. To bring such a spot is very difficult! The molecules of the same solid animal fats because of the other buildings do not enter into chemical interaction neither between themselves nor with the fabric fibers, so stains can withdraw and after a long time.
Appearance oily spots have no pronounced boundaries, the contours of their vague. Fresh grease stains easier to remove and they are always darker than the tissue on which they are located, the old lighter due to dust deposited on them.