question: why cooking oil changes the color of your clothes permanently darker.
comment: Oil makes things darker the same way wet things are darker. It adds a layer of gloss and since oils dry via oxidation instead of evaporation it is difficult to remove once cured. It's also why it's used commonly in painting for those properties.
passages: Blackening (cooking)
  
  Blackening is a cooking technique used in the preparation of fish and other foods. Often associated with Cajun cuisine, this technique was popularized by chef Paul Prudhomme. The food is dipped in melted butter and then sprinkled with a mixture of herbs and spices, usually some combination of thyme, oregano, chili pepper, peppercorns, salt, garlic powder and onion powder. It is then cooked in a very hot cast-iron skillet. The characteristic brown-black color of the crust results from a combination of browned milk solids from the butter and charred spices.
   Sunlight acts as a bleach through a similar process. High energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless.
  
  Some detergents go one step further; they contain fluorescent chemicals which glow, making the fabric look literally whiter than white.
  
  Section::::In the natural world.
  
  Section::::In the natural world.:Astronomy.
   The traditional technique for applying pure tung oil is to dilute the oil 1:1 with solvent, then apply a succession of very thin films with a soft, lint-free, non-fuzzy cloth such as tee-shirt cotton. Diluents range from traditional spirits of turpentine to any of the new citrus-based thinners to naphtha. The choice of thinner should be guided by how fast the coating needs to set. Naphtha works well in spray-on applications in well ventilated studios. Primary coats may be laid down at a 1:1 oil-to-thinner ratio, and successive layers, if not absorbed into the wood, at higher solvent to oil concentrations. This technique brings out the deepest color of the wood while maintaining a matte finish.
   Powdered and mixed with oil, the alkanet root is used as a wood stain. When mixed into an oily environment, it imparts a crimson color to the oil, which when applied to a wood, moves the wood color towards dark-red-brown rosewood, and accentuates the grain of the wood.
  
  Alkanet is traditionally used in Indian food under the name "ratan jot", and lends its red colour to some versions of the curry dish "rogan josh". In Australia, alkanet is approved for use as a food colouring, but in the European Union, it is not.
   Section::::Importance of cooking temperature on interfaces.:Smoke points of oils.
   According to the manufacturer, about 1/2 of a bar of Fels-Naptha grated and added to a wash cycle helps eliminate residual stains.
  
  Fels-Naptha is also a common ingredient in DIY laundry detergent recipes.
  
  Fels-Naptha, when combined with Neatsfoot oil, is commonly used in a primitive method of tanning animal skins.
  
  Section::::Health considerations.
  
  In its 2007 material safety data sheet, Dial Corp. states that Fels-Naptha can irritate the eyes and, with prolonged exposure, the skin.
   Under prolonged heat, the triglycerides in the oil begin to break down. This means the glycerol molecules and the fatty acid chains begin to break apart. As this occurs the oil becomes more polar. As the oil becomes more polar, the Van der Waals interactions between the glycerol and the hydrocarbons begin to increase. In this case, the dipole on glycerol induces a dipole in the hydrocarbon chain. The strength of the dipole induced dipole interactions can be modeled with a combination of Debye, Keesom and London interactions through addition.
  
  Debye:
  
  Keesom:
  
  London:
   Skin and fingernails are made of a similar type of keratinized protein as hair. That means that drips, slips and extra hair tint around the hairline can result in patches of discolored skin. This is more common with darker hair colors and persons with dry absorbent skin. That is why it is recommended that latex or nitrile gloves be worn to protect the hands.
   Cooking techniques can be broken down into two major categories: Oil based and water based cooking techniques. Both oil and water based techniques rely on the vaporization of water to cook the food. Oil based cooking techniques have significant surface interactions that greatly affect the quality of the food they produce. These interactions stem from the polar oil molecules interacting with the surface of the food. Water based techniques have far less surface interactions that affect the quality of the food.
  
  Section::::Interaction of cooking techniques.:Pan fry.
   The process of heating a pan to cause the oil to oxidize is analogous to the hardening of drying oil used in oil paints, or to varnish a painting. But whereas the curing of oils is the result of autoxidation at room temperature for a painting, for a pan, the thermoxidized oil undergoes a conversion into the hard surface of the seasoned pan at the high temperatures of cooking.
   When applied in coats over wood, Danish oil cures to a hard satin finish that resists liquid well. As the finished coating is not glossy or slippery, it is a suitable finish for items such as food utensils or tool handles, giving some additional water resistance and also leaves a dark finish to the wood. Special dyed grades are available if wood staining is also needed.
  
  Section::::Application.
   Section::::Conditions that lead to oil content increase.:Blue light and Ultraviolet A (UV-A).
   Pan frying is an oil based cooking technique which is typically used to sear larger cuts of meat or to fully cook thinner cuts. This technique uses a thin layer of heated oil to coat the pan. The oil layer is the method of heat transfer between the burner and the food.
   Grease traps or interceptors collect fats and oils from kitchen sinks and floor drains which would otherwise clog sewer lines and interfere with septic systems and sewage treatment. The collected product is called brown grease in the recycling industry. Brown grease is contaminated with rotted food solids and considered unsuitable for re-use in most applications.
  
  Section::::Waste cooking oil.:Adulteration.
  
  Gutter oil and trench oil are terms used in China to describe recycled oil processed to resemble virgin oil, but containing toxic contaminants and sold illegally for cooking; its origin is frequently brown grease from garbage.
   The other effect that the seasoning oil has is to make the surface of a cast iron pan hydrophobic. This makes the pan non-stick during cooking, since the food will combine with the oil and not the pan. It also makes the pan easier to clean, but eventually the polymerized oil layer which seasons it comes off and it needs to be re-seasoned.
  
  Section::::Materials in cooking.:Ceramic.
   In terms of surface interactions, chromium oxide is polar. The oxygen atoms on the surface have a permanent dipole moment, and are therefore hydrophilic. This means that water will wet it, but oils or other lipids will not.
  
  Section::::Materials in cooking.:Cast iron.
   BULLET::::- "Dipping or tip dyeing", similar to balayage in that the color is painted directly on the hair (This results in a more solid level of coverage on the ends of the hair.)
  
  All coloring techniques can be used with any type of color. For lightening, the hair sometimes has to be bleached before coloring.
  
  Section::::Application techniques.:On-scalp.
  
  Hair coloring can also be applied on the scalp for a more solid level of coverage 
   Cooking oil
  
  Cooking oil is plant, animal, or synthetic fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavouring not involving heat, such as salad dressings and bread dips, and in this sense might be more accurately termed edible oil.
  
  Cooking oil is typically a liquid at room temperature, although some oils that contain saturated fat, such as coconut oil, palm oil and palm kernel oil are solid.
   BULLET::::- Emulsified - At the point of saturation, a cloudy appearance will be the tell-tale sign that the water/oil mixture has become emulsified.
  
  BULLET::::- Free - The most developed stage of fuel contamination is when free flowing puddles of water appear within stored oil. At this point, bacterial contamination and growth is boosted.
  
  Section::::Microbial contamination.
  
  The contaminants found in fuel can be made up of a number of things, predominantly "Hormoconis Resinae", which is typically the main contaminant when microbial contamination is present, along with bacteria "Pseudomonas Aeruginosa", and fungi such as yeasts and moulds like "Yarrowia tropicalis".
   The smoke point of any oil is defined by the temperature at which light blue smoke rises from the surface. The smoke, which contains acrolein, is an eye irritant and asphixiant. The smoke point of oils vary widely. Depending on origin, refinement, age, and source growth conditions, the smoke point for any given type of oil can drop nearly 20 °C. For example, the smoke point of olive oil can vary from being suitable for high temperature frying to only safely used for stir frying. As a cooking oil is refined its smoke point increases. This is because many of the impurities found in natural oils aid in their breakdown. In general the lighter the oil, the higher its smoke point. It is important to choose the appropriate oil for each cooking technique and temperature as cooking oils degrade rapidly when heated about their smoke point. It is recommended that oils heated beyond their smoke point should not be consumed as the chemicals created are suspected carcinogens.
   The chemical preparations used for special styles will be mentioned in their proper places; but a general prepare, employed for most colours that are developed and fixed by steaming only, consists in passing the bleached calico through a weak solution of sulphated or turkey red oil containing 2.5 to 5 percent fatty acid. Some colours are printed on pure bleached cloth, but all patterns containing alizarine red, rose and salmon shades are considerably brightened by the presence of oil, and indeed very few, if any, colours are detrimentally affected by it.
   There are many cooking techniques that do not use oil as part of the process such as steaming or boiling. Water based techniques are typically used to cook vegetables or other plants which can be consumed as food. When no oil is present the method of heat transfer to the food is typically water vapor. Water vapor molecules do not have any significant surface interactions with the food surface. Since food, including vegetables, is cooked by the vaporization of water within the food, the use of water vapor as the mode of heat transfer has no effect on the chemical interactions on the surface of the food.
   Cooking oil can be recycled. It can be used as animal feed, directly as fuel, and to produce biodiesel, soap, and other industrial products.
  
  In the recycling industry, used cooking oil recovered from restaurants and food-processing industries (typically from deep fryers or griddles) is called recycled vegetable oil (RVO), used vegetable oil (UVO), waste vegetable oil (WVO), or yellow grease.
  
  Yellow grease is used to feed livestock, and to make soap, make-up, clothes, rubber, detergents, and biodiesel fuel.
  
  Used cooking oil, besides being converted to biodiesel, can be used directly in modified diesel engines and for heating.
   The smoke point of cooking oils varies generally in association with how oil is refined: a higher smoke point results from removal of impurities and free fatty acids. Residual solvent remaining from the refining process may decrease the smoke point. It has been reported to increase with the inclusion of antioxidants (BHA, BHT, and TBHQ). For these reasons, the published smoke points of oils may vary.
   Oil Red O largely replaced Sudan III and Sudan IV, as it provides much deeper red color and the stains are therefore much easier to see. 
  
  In pyrotechnics, Oil Red O is used in some compositions of red colored smokes. It is also used for making dyes.
  
  Section::::Forensic.
  
  When staining, Oil Red O can make fat more visible in various cuts in pathology.
  