question: How does the sun cause fading in items? Is there a sort of “sunblock” that can be used to prevent this?
comment: The sun gives off UV rays, which can break chemical bonds in the pigment molecules that give manufactured objects their color. Sunblock works by absorbing UV rays, either physically or chemically, so often there are coatings you can put on an object to keep them from fading, like thin plastic films or chemical coatings.
passages: UV degradation
  
  Many natural and synthetic polymers are attacked by ultraviolet radiation, and products using these materials may crack or disintegrate if they are not UV-stable. The problem is known as "UV degradation", and is a common problem in products exposed to sunlight. Continuous exposure is a more serious problem than intermittent exposure, since attack is dependent on the extent and degree of exposure.
  
  Many pigments and dyes can also be affected, and the problem known as phototendering can affect textiles such as curtains or drapes.
  
  Section::::Susceptible polymers.
   UV is a form of electromagnetic radiation with higher energy than visible light. It does not contribute to the accurate viewing of collections and is ideally completely eliminated; otherwise materials may be weakened in any number of ways ranging from yellowing to disintegration. Organic materials, especially textiles and paper, are particularly vulnerable to UV-caused decay. Direct sunlight holds the most potential for UV damage, but certain types of artificial light bulbs may also produce these harmful rays.
   In fibre products like rope used in outdoor applications, product life will be low because the outer fibres will be attacked first, and will easily be damaged by abrasion for example. Discolouration of the rope may also occur, thus giving an early warning of the problem.
  
  Polymers which possess UV-absorbing groups such as aromatic rings may also be sensitive to UV degradation. Aramid fibres like Kevlar, for example, are highly UV-sensitive and must be protected from the deleterious effects of sunlight.
  
  Section::::Detection.
   In fibre products like rope used in outdoor applications, product life will be low because the outer fibres will be attacked first, and will easily be damaged by abrasion for example. Discolouration of the rope may also occur, thus giving an early warning of the problem. 
  
  Polymers which possess UV-absorbing groups such as aromatic rings may also be sensitive to UV degradation. Aramid fibres like Kevlar, for example, are highly UV-sensitive and must be protected from the deleterious effects of sunlight.
  
  Section::::Mechanism.
   The components of the weather cycles responsible for the deterioration of most materials are non-ionizing radiation, atmospheric temperature and moisture in its various forms. This, combined with the effects of wind and atmospheric gases and pollutants. Although the ultraviolet (UV) portion of solar radiation is mainly responsible for initiating weathering effects, the visible and near-infrared portions can also contribute to the weathering processes. Colored materials are susceptible to visible radiation, and near-infrared radiation can accelerate chemical reactions by raising the material temperature. The other factors act synergistically with solar radiation to significantly influence the weathering processes. All weather factors, including the quality and quantity of sunlight, vary with geographic location, time of day and year, and climatalogical conditions. In order to fully understand and predict the effect of weather on materials, data is required on each factor that may contribute to degradation.
   Light can have a variety of effects on textiles over time. In some cases, it may contribute to fading or discoloration, but of more concern is the damage which the fibers may suffer under prolonged exposure to non-visible light, such as ultraviolet and infrared lighting. Ideally, textiles should be stored or displayed in as little light as possible, and preferably in total darkness. However, as this is impractical for display and care of the piece, knowing the limits of lighting as well as the safest amounts of lighting, become important.
   In some cases, the textiles are weakened not by outside causes such as light or pests, but by chemical reactions taking place within the fabric itself, such as the oxidation of iron-based mordants over time, which can cause darkening and discolouration in the surrounding fibres.
   Fluorescent and halogen-produced light can also produce large amounts of UV radiation, though filters which fit over the bulbs are available to limit the damaging light. These filters will need to be replaced when the bulbs are changed, so maintenance staff should be aware of them and their use.
   Natural light is the most common source of ultraviolet light, and as such, care should be taken to avoid exposure to direct sunlight at all costs, and indirect sunlight whenever possible. This may mean storing or displaying textiles in an area without windows, or with blackout curtains, which can be pulled whenever the room is not in use. If a room relies on natural light, UV screens or coatings can be applied to the windows to block harmful rays while still allowing light to pass through. These filters should be checked periodically, however, as they have a limited lifespan and may need to be replaced every few years.
   Relative amount of fading can be measured and studied by using standard test stripes. In the workflow of Blue Wool test one reference stripe set shall be stored protected from any exposure of light. Simultaneously with samples another equivalent test stripe set is exposed under the light source defined in the standard. For example, if the lightfastness of the colourant is indicated to be 5 on Blue Wool scale, it can be expected to fade similar amount as the strip number 5 in Blue Wool test strip set. The accomplishment of the test can be confirmed by comparing the test stripe set with the reference set stored protected from the light.
   Phototendering
  
  Phototendering is the process by which organic fibres and textiles lose strength and flexibility as a result of exposure to sunlight. It is the ultraviolet component of the sun's spectrum which affects fibres, causing chain degradation and hence loss of strength. Fading of colours is a common problem in phototendering. 
  
  Section::::UV Degradation.
   Sun protective clothing
  
  Sun protective clothing is clothing specifically designed for sun protection and is produced from a fabric rated for its level of ultraviolet (UV) protection. A novel weave structure and denier (related to thread count per inch) may produce sun protective properties. In addition, some textiles and fabrics employed in the use of sun protective clothing may be pre-treated with UV-inhibiting ingredients during manufacture to enhance their effectiveness.
   A number of fabrics and textiles in common use today need no further UV-blocking enhancement based on their inherent fiber structure, density of weave, and dye components, especially darker colors and indigo dyes. Good examples of these fabrics contain full percentages or blends of heavy-weight natural fibers like cotton, linen and hemp or light-weight synthetics such as polyester, nylon, spandex and polypropylene. Natural or synthetic indigo-dyed denim, twill weaves, canvas and satin are also good examples. However, a significant disadvantage is the heat retention caused by heavier-weight and darker-colored fabrics.
   Often, people wear an item of clothing until it falls apart. Some materials present problems. Cleaning leather is difficult, and bark cloth (tapa) cannot be washed without dissolving it. Owners may patch tears and rips, and brush off surface dirt, but materials like these inevitably age.
  
  However, most clothing consists of cloth, and most cloth can be laundered and mended (patching, darning, but compare felt).
  
  Section::::Life cycle.:Laundry, ironing, storage.
   Light can cause cumulative damage to wooden artifacts, leading to discoloration of the surface. Long exposure to light can result in darkening of light woods and bleaching of dark woods. Infra red radiation and heat from light can also damage any finishes to the object, causing cracking of paint or varnish, brittleness, or softening of the surface.
  
  To reduce the damage inflicted by light, it is recommended that the three following steps be taken:
  
  BULLET::::- Eliminate UV radiation- This can be done simply by keeping objects out of direct sunlight and displaying them behind UV filtering plexiglas.
   There is some indication that washing fabrics in detergents containing fabric brighteners, which absorb UV radiation, might increase their protective capability. Studies at the University of Alberta also indicate that darker-colored fabrics offer more protection than lighter-colored fabrics.
  
  While there is some correlation between the percentages of visible light and UV that pass through the same fabric, it is not a strong relationship. With new-technology textiles designed for the sole purpose of UV blocking, it is not always possible to judge the UV protection level simply by holding up the fabric and examining how much visible light passes through.
   Section::::Environment.
  
  The chief cause for decay in textiles is almost always the environment in which they are stored. Light, temperature, and humidity can all contribute to a textile’s health or deterioration, depending on their intensity. Additionally, pests, chemicals, and pollutants may also cause damage to an antique fabric. Airborne chemicals, such as smog or cigarette smoke are also harmful to the textiles, and should be avoided if at all possible: high-efficiency air filters should be installed throughout the building to reduce the presence of airborne chemicals that may stain, discolor, or weaken fabrics.
  
  Section::::Environment.:Light.
   AATCC 183 should be used in conjunction with other related standards including ASTM D 6544 and ASTM D 6603. ASTM D 6544 specifies simulating the life cycle of a fabric so that a UPF test can be done near the end of the fabric's life, when it typically provides the least UV protection. ASTM D 6603 is a consumer format recommended for visible hangtag and care labeling of sun protective clothing and textiles. A manufacturer may publish a test result to a maximum of UPF 50+.
   Packages can degrade with exposure to temperature, humidity, time, sterlization (steam, radiation, gas, etc.), sunlight, and other environmental factors. For some types of packaging, it is common to test for possible corrosion of metals, polymer degradation, and weather testing of polymers. Several types of accelerated aging of packaging and materials can be accomplished in a laboratory.
  
  Exposure to elevated temperatures accelerates some degradation mechanisms. An Arrhenius equation is often used to correlate certain chemical reactions at different temperatures, based on the proper choice of Q coefficients.
  
  As with any laboratory testing, validating field trials are important.
  
  Section::::Vacuum testing.
   Window films filter out over 99% of UV rays to 380 nm, reducing the main factor in fading. However, additional factors such as solar heat, visible light, humidity, and presence or absence of chemical vapors also contribute to fading. Therefore, the greatest protection from fading is offered by tinted or metallised window films that reject large levels of heat and visible light, in addition to UV.
  
  Section::::Selection of window film.
   White LEDs can be used as white holiday lights or to create any other color through the use of colored refractors and lenses similar to those used with incandescent bulbs. Color fading may occur due to the exposure of colored plastics to sunlight or heat, as with ordinary holiday lights. Yellowing may also occur in the epoxy body in which the LED is encased if left in the sun consistently.
   UV-C radiation is able to break down chemical bonds. This leads to rapid aging of plastics, insulation, gaskets, and other materials. Note that plastics sold to be "UV-resistant" are tested only for UV-B, as UV-C doesn't normally reach the surface of the Earth. When UV is used near plastic, rubber, or insulation, care should be taken to shield these items; metal tape or aluminum foil will suffice.
   The rate of deterioration is also affected by pigments and dyes present in the textiles. Pigments themselves can also be affected, generally fading after exposure to both UVA and UVB radiation. Great care is needed to preserve museum artefacts from the harmful effects such as ancient textiles, of UV light, which can also be present in fluorescent lamps. Paintings such as watercolours need protection from sunlight so that the original colours are preserved. 
   Proper storage of plastics can help slow down the degrading process of plastics. Plastics are currently stored with a RH Level of 50% with the storage temperature at 18 degrees Celsius with no light coming into contact with the objects. Although the composition of each plastic material can be different it is difficult to determine one unifying storage care plan ,thus understanding the composition of the plastic can help determine their preferred climate levels. Keeping plastics at a stable low temperature or considering placing these objects either in cold storage or in oxygen impermeable bags helps slow degradation.
   Paints, inks and dyes that are organic are more susceptible to photodegradation than those that are not. Ceramics are almost universally colored with non-organic origin materials so as to allow the material to resist photodegradation even under the most relentless conditions, maintaining its color.
  
  Section::::Applications.:Pesticides and herbicides.
  