question: why does skin turn green because of certain jewelry? What is the scientific reason behind it?
comment: Copper oxide is green. Copper oxidises in the presence of air, and the reaction is accelerated in contact with the moisture on your skin. There are numerous alloys of copper used in jewellery, as well as pure copper.
passages: Starbucks is one of the largest food retailers in the U.S. to enforce these FDA guidelines for food safety and it is expected that more retailers will likely follow their lead in the coming year.
  
  Section::::Technological advancements in the field.
   In an attempt to recoup profits and meet demand, some American turquoise is treated or "enhanced" to a certain degree. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). There are however, some American mines which produce materials of high enough quality that no treatment or alterations are required. Any such treatments which have been performed should be disclosed to the buyer on sale of the material.
  
  Section::::Occurrence.:Other sources.
   Metals are shiny and lustrous, at least when freshly prepared, polished, or fractured. Sheets of metal thicker than a few micrometres appear opaque, but gold leaf transmits green light.
   Section::::Jewelry.
   Section::::History.
   Color change materials have been used in several very common outlets but also in an increasing number of new ones. Commercial applications include photochromics in ophthalmics, fashion/cosmetics, security, sensors, optical memory and optical switches, thermochromics in paints, inks, plastics and textiles as indicators/sensors and in architecture, ionochromics in copy paper, direct thermal printing and textile sensors, electrochromics in car mirrors, smart windows, flexible devices and solar protection, solvatochromics in biological probes and sensors, gasochromics in windows and gas sensors.
  
  Section::::Dyes and pigments.
   Being a phosphate mineral, turquoise is inherently fragile and sensitive to solvents; perfume and other cosmetics will attack the finish and may alter the colour of turquoise gems, as will skin oils, as will most commercial jewellery cleaning fluids. Prolonged exposure to direct sunlight may also discolour or dehydrate turquoise. Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hair spray, should be applied before putting on turquoise jewellery, and they should not be worn to a beach or other sun-bathed environment. After use, turquoise should be gently cleaned with a soft cloth to avoid a buildup of residue, and should be stored in its own container to avoid scratching by harder gems. Turquoise can also be adversely affected if stored in an airtight container.
   Turquoise is treated to enhance both its colour and durability (increased hardness and decreased porosity). As is so often the case with any precious stones, full disclosure about treatment is frequently not given. Gemologists can detect these treatments using a variety of testing methods, some of which are destructive, such as the use of a heated probe applied to an inconspicuous spot, which will reveal oil, wax or plastic treatment.
  
  Section::::Treatments.:Waxing and oiling.
   can be interpreted as photodarkening, and such interpretation is not yet confirmed. Recent work pointed out the role of thulium contamination. Through laser pump and signal absorption, and energy transfer from ytterbium; thulium is able to emit UV light, known to create color centers in silica glass. Although the actual mechanism of photodarkening is still unknown, a reliable setup to test the photodarkening properties of different types of fibers has been recently reported.
   In many cultures of the Old and New Worlds, this gemstone has been esteemed for thousands of years as a holy stone, a bringer of good fortune or a talisman. The oldest evidence for this claim was found in ancient Egypt, where grave furnishings with turquoise inlay were discovered, dating from approximately 3000 BC. In the ancient Persian Empire, the sky-blue gemstones were earlier worn round the neck or wrist as protection against unnatural death. If they changed color, the wearer was thought to have reason to fear the approach of doom. Meanwhile, it has been discovered that turquoise can change color. The change can be caused by light, or by a chemical reaction brought about by cosmetics, dust or the acidity of the skin.
   Section::::Macramé.:Macramé jewelry.
   Badly cleaned materials can transfer remaining bacteria and such to the body of the jewelry-wearer, so therefore it is very important that you buy your jewelry from a company with ethical good manufacturing practices.
  
  Lower quality jewelry might have scratches or cracks which can harbor bacteria, or poor finishes which can result in harsh textures.
   Section::::Regulation.
   Section::::Toxicity.:Environment.
   The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. The majority of American material is now treated in this manner although it is a costly process requiring many months to complete.
  
  Section::::Treatments.:Dyeing.
   David Bellman is an entrepreneur and founder of Bellman Jewelers, Inc. and has over 35 years of jewelry retailing and manufacturing experience. Since 2010, Bellman has been studying the effects contaminated jewelry can have on the human population. With his discovery of “Jewelry Hygiene®,” Bellman has become the foremost authority on the dangers of infected jewelry. 
  
  After over two years of development, the AquaSonic Wave was introduced to the public in January 2015. AquaSonic Corporation is the sole distributor of the AquaSonic Wave and has distribution agreements with both QVC and Brookstone.
   Section::::Description.
   Certain natural gemstone colors, such as blue-to-green colors in diamonds, are the results of the exposure to natural radiation in the earth, which is usually alpha or beta particle. The limited penetrating ability of these particles result in partial coloring of the diamond's surface. Only high-energy radiation such as gamma ray or neutron can produce fully saturated body colors, and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry.
   Topical anesthetics are often used by technicians prior to cosmetic tattooing and there is the potential for adverse effects if topical anesthetics are not used safely. In 2013 the International Industry association CosmeticTattoo.org published a detailed position and general safety precautions for the entire industry.
  
  The causes of a change of colour after cosmetic tattooing are both complex and varied. As discussed in the detailed industry article "Why Do Cosmetic Tattoos Change Colour", primarily there are four main areas that have influence over the potential for a cosmetic tattoo to change colour;
  
  BULLET::::1. Factors related to the pigment characteristics
   Due to its stability, phthalo green is used in inks, coatings, and many plastics. In application it is transparent. Being insoluble, it has no tendency to migrate in the material. It is a standard pigment used in printing ink and packaging industry. It is also allowed in all cosmetics except those used around the eyes. It is used in some tattoos.
  
  Section::::Related compounds.
  
  Copper phthalocyanine green 36 is a variant where some of the chlorine atoms are replaced with bromine. Bromination is less efficient than chlorination. Consequently the degree of bromination is lower.
  
  Section::::See also.
   Along with its presence in avian egg shells, other studies have also shown that biliverdin is present in the blue-green blood of many marine fish, the blood of tobacco hornworm, the wings of moth and butterfly, the serum and eggs of frogs, and the placenta of dogs. With dogs this can lead, in extremely rare cases, to the birth of puppies with green fur; however, the green colour fades out soon after birth. In the garfish ("Belone belone") and related species, the bones are bright green because of biliverdin.
   As the color change is persistent and energy need only be applied to affect a change, electrochromic materials are used to control the amount of light and heat allowed to pass through windows ("smart windows"), One popular application is in the automobile industry where it is used to automatically tint rear-view mirrors in various lighting conditions.
  
  Section::::Electrochromic materials.
  
  Among the metal oxides, tungsten oxide (WO), has been the most extensively studied material.
   Section::::Writing and recording.
   Section::::Properties determining value.:Treatments.
   Dichromatism
  
  Dichromatism (or polychromatism) is a phenomenon where a material or solution's hue is dependent on both the concentration of the absorbing substance and the depth or thickness of the medium traversed. In most substances which are not dichromatic, only the brightness and saturation of the colour depend on their concentration and layer thickness.
  
  Examples of dichromatic substances are pumpkin seed oil, bromophenol blue, and resazurin.
  
  When the layer of pumpkin seed oil is less than 0.7 mm thick, the oil appears bright green, and in layer thicker than this, it appears bright red.
  