As the prevalence of genetically modified organisms GMOs continues to rise, there has been an increasing public interest for information concerning the safety of these products. Concerns generally focus on how the GMO may affect the environment or how it may affect the consumer.
Physical basis[ edit ] A wide variety of wavelengths colors encounter a pigment.
This pigment absorbs red and green light, but reflects blue—creating the color blue. Pigments appear colored because they selectively reflect and absorb certain wavelengths of visible light.
When Term paper 2015 light encounters a pigment, parts of the spectrum are absorbed by the pigment. Organic pigments such as diazo or phthalocyanine compounds feature conjugated systems of double bonds.
The new reflected light spectrum creates the appearance of a color. Pigments, unlike fluorescent or phosphorescent substances, can only subtract wavelengths from the source light, never add new ones. The appearance of pigments is intimately connected to the color of the source light.
Sunlight has a high color temperature and a fairly uniform spectrum and is considered a standard for white light, while Term paper 2015 light sources tend to have strong peaks in parts of their spectra. Viewed under different lights, pigments will appear different colors.
Color spaces used to represent colors numerically must specify their light source.
Lab color measurements, unless otherwise noted, assume that the measurement was taken under a D65 light source, or "Daylight K", which is roughly the color temperature of sunlight.
Sunlight encounters Rosco R80 "Primary Blue" pigment. The product of the source spectrum and the reflectance spectrum of the pigment results in the final spectrum, and the appearance of blue.
Other properties of a color, such as its saturation or lightness, may be determined by the other substances that accompany pigments.
Binders and fillers added to pure pigment chemicals also have their own reflection and absorption patterns, which can affect the final spectrum. These stray rays of source light make the mixture appear to have a less saturated color.
Pure pigment allows very little white light to escape, producing a highly saturated color, while a small quantity of pigment mixed with a lot of white binder will appear unsaturated and pale due to incident white light escaping unchanged.
History[ edit ] Naturally occurring pigments such as ochres and iron oxides have been used as colorants since prehistoric times. Archaeologists have uncovered evidence that early humans used paint for aesthetic purposes such as body decoration. Pigments and paint grinding equipment believed to be betweenandyears old have been reported in a cave at Twin Rivers, near LusakaZambia.
Most of the pigments in use were earth and mineral pigments, or pigments of biological origin. Pigments from unusual sources such as botanical materials, animal waste, insectsand mollusks were harvested and traded over long distances.
Some colors were costly or impossible to obtain, given the range of pigments that were available. Blue and purple came to be associated with royalty because of their rarity. Biological pigments were often difficult to acquire, and the details of their production were kept secret by the manufacturers.
Tyrian Purple is a pigment made from the mucus of one of several species of Murex snail. Greek historian Theopompuswriting in the 4th century BCE, reported that "purple for dyes fetched its weight in silver at Colophon [in Asia Minor].
The only way to achieve a deep rich blue was by using a semi-precious stone, lapis lazulito produce a pigment known as ultramarineand the best sources of lapis were remote.
Flemish painter Jan van Eyckworking in the 15th century, did not ordinarily include blue in his paintings. To have one's portrait commissioned and painted with ultramarine blue was considered a great luxury. If a patron wanted blue, they were obliged to pay extra.
When Van Eyck used lapis, he never blended it with other colors. Instead he applied it in pure form, almost as a decorative glaze. Miracle of the Slave by Tintoretto c. The son of a master dyerTintoretto used Carmine Red Lake pigment, derived from the cochineal insect, to achieve dramatic color effects.
Spain's conquest of a New World empire in the 16th century introduced new pigments and colors to peoples on both sides of the Atlantic. Carmine —a dye and pigment derived from a parasitic insect found in Central and South America —attained great status and value in Europe.FAO PLANT PRODUCTION AND PROTECTION PAPER ISSN Pesticide residues in food REPORT Joint FAO/WHO Meeting on Pesticide Residues.
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