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What Determins the Color of Substances and Objects
WHAT IS COLOR
Light of differnt wavelength within the visible spectrum appear with differnt color. Red, yellow, green, blue, violet are the colors of light with decreasing wavelength and increasing wave frequency. You also have all shades betwwen. Furthermore you have infrared at the longest wavelength invisible for human, and ultraviolet at the shortest, also invisible for humans.
Blending of different light also give appearance of special colors. Blue and red looks like violet, just like real violet. Red and green also looks like yellow. Yellow and blue also looks like green. All colors blended looks like white, and no light looks like black.
The color of a substance or an object depends on the lights coming from the substance. Usually much of this light originally comes from the light in the environment. Therefor what kind of light there is around will determine whnaqt colors it is possible for objects to transmit to the eyes of beholders.
Some light may also stem from pocesses within the substance. For example will a substance with a certain temperature glow red.
HOW A SUBSTANCE TREATS LIGHT FALLING ONTO IT
The light, and hence the color, coming from a susbtance depends largely how the substance treat light falling onto it. When light falls onto a substance, some will be refelcted right away in the same angel that if fell onto it. Some will be absorbed. Some will be let through. The path of the light let through will also be shifted, called refracted, some angles. The differnet susbtances do these things to light of different wavelengths, or color, in different degree.
REFLECTION
The color depends on what wavelength the susbtance reflects. If it reflects red, for example, red light will be a part of, or perhaps only the type of light, coming from the object.
ABSORBTION AND TRASPARENCY
The color depends upon what light the substance absorbs. Light of wavelengths that are absorbed by the substance, will not contribute to its color.
The color appearance of a substance deends upon if the substance is transparant for light, and what wavelengths it lets true. The property of transparency is of cource the opposite of that of absorbance ability. Light of a certain color that falls on one side of the substance, and which is not absorbed, will come true at the opposite side and contribute to the color.
BENDING OF LIGHT DIRECTION OR REFRACTION
The property of refraction will spread light of different wavelength in different degree withing a substance. That can cause light of certain wavelengths to come out of a substance or object in another direction that what you looks into the object from. You will mainly see the light coming towards you and the color off that light.
Refraction can be caused by a prism effect caused ny outside areas of the substance that are held in an angle to the direction of light coming into the substance.
Thus an object can shift color depending on the direction where you look or the direction from where light shines on the object. The colorful twincling of diamonds is for example caused thus.
But it can also get caused by a grating effect, Structures within the substance can work as a grating with bands that do not let light through and and adjacent bands that let the light pass. Gratings with microscopically fine filaments within a microscopic distance from each other will also cause refraction.
The play of colors in butterfly wings, in the body of many insects, or in mother of pearl is mainly caused this way.
COLOR CAUSED BY TEHMERATURE
The temperature of a substance will always cause the substance to emit electromagnetic rays. At room temperature, most will be infrared light and not visible, but at some higher temperture an object will glow first red, then yellow, green, blue and white with rising temperature.
FLUORESCENCE AND PHOSPHORESCENCE
Fluorescense is a porcess where light with a certain wavelength is absorbed by the substance, but the energy absorbed is emitted again as light of another wavelength, which of corce will contribute to the total color of the object.
Radioactive decay within a substance can make the it glow with various colors already by room temnperature. If the decay is intense enough, the object can be warmed up so that it glows because of heat too.
Also chemical reactions within an a substance can cause light of specific wavelengths to be emitted. A process within a substance that cause light to be emitted is called phosphoresence.
COLOR DEPENDING ON THE CHEMICAL PROPERTIES OF SUBSTANCES
Substances that absorb specific frequences of light will typically have special atoms of groups of atoms in their molecules. Metal atoms withy a complex electron shell will often exhibit bright color, because the energies of the electrons of these atoms can easily jump to a higher level by absorbing photons, and then get rid of this energy again by converting it to heat. The photons not absorbed gives the color. Metal atoms within other molecules, like iron, cobalt, vanadium, chrome are example of such atoms.
Complex organic molecules, containing nitrogen, sulphur or phsophoros and with alternating double and single bonds will get the same properties and show bright color.
Other kind of molecules that can aborb specific frequencies of light, are those with atoms that easily can shift between negatively or positively loaded and neutral state. The shift is associated with absorbtion of light energy.