Saturday, July 7, 2012

The Nature of Color[1-5]
Art Resource

Marie-Therese Wisniowski

Preamble
This is the fifth post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.

Other posts in this series are:
Glossary of Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General

The Glossary of Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, Glossary of Colors, Dyes, Inks, Pigments and Resins, Glossary of Fabrics, Fibers, Finishes, Garments and Yarns and Glossary of Art, Artists, Art Motifs and Art Movements have been updated in order to better inform your art practice.

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The Art Resource series will be the first post in each calendar month. Remember - these Art Resource posts span information that will be useful for a home hobbyist to that required by a final year University Fine-Art student and so undoubtedly, some parts of any Art Resource post may appear far too technical for your needs (skip over those mind boggling parts) and in other parts, it may be too simplistic with respect to your level of knowledge (ditto the skip). The trade-off between these two extremes will mean that Art Resource posts will hopefully be useful in parts to most, but unfortunately may not be satisfying to all!


Nature Of Light
Light is a form of energy that is schizophrenic in terms of our measurement of it: in some measurements it acts like streams of ethereal or massless bullets (called photons) and so it possesses the property of pressure; in other measurements, it acts like a wave that you would ride with a surf board. If two light waves cross - and they are in phase (i.e. their crests and troughs match) - the height of the combined waves grows in size (constructive interference). On the other hand, if they are out of phase (the crest of one wave falls into the trough of the other) the height of the combined waves decreases in size (destructive interference).

The length between successive crests or troughs is the wavelength of a light. The latter is associated with color. With respect to the light that we can perceive, blue light possesses a smaller wavelength when compared to red light etc.

The Light Spectrum.

The seven principal colors of visible or white light are: violet, indigo, blue, green, yellow, orange and red. (Note: Sometimes people will not separate violet from indigo and so claim there are only six components). Rainbows are formed when white light is separated into the seven principal colors when it travels through raindrops, which act like tiny prisms.

When white light passes through a prism it separates into its primary colors.
Note: Australian males affectionately call their mates with red hair "bluey", since blue sits on the opposite end of the white light spectrum to red - go figure!

The energy of the ethereal light bullets is inversely proportional to its wavelength; blue light is more energetic and so has a shorter wavelength than red light. Ultraviolet (or UV) light is more energetic than infrared light and infrared light is more energetic than microwave light etc.

Cell or mobile phones use microwave light to transmit conversations and so the mobile transmitters/receivers must be near each other since the microwave ethereal bullets are not that energetic. On the other hand, UV is so energetic that it can cause skin cancer as well as pre-age your skin. Hence, sunscreens nowadays have a sun protection factor (SPF) of 30 to filter out UV A and UV B light from being absorbed by your skin.

Primary Colors of Visible or White Light.
Note: One Angstrom is 10-8cm or 10-10meters. See - Glossary of Terms.

The intensity of light is dependent on the number of light bullets that reach the retina. If a lot of light bullets reach the retina, the color is intense, whereas if few light bullets reach our eyes, the color is lighter or duller in intensity.

Let us consider the difference between "light blue" and "vivid blue". "Light blue" has white dots mixed up with blue dots. If we shone bullets of white light on a "light blue" object, all the white dots would reflect all the white light bullets back into our eyes, but the small amount of blue dots would absorb all six other colors and only reflect a few blue bullets back into our eyes. Our brain would perceive that mixture as being "light blue" since it is receiving mostly "white" bullets (all colors) than blue bullets. On the other hand, "vivid blue" has no white dots - its all blue. Hence if we shone bullets of white light on it, we would get only blue bullets reaching our eyes and no other color. Therefore, our brain would perceive it as an intense blue. The "blue" bullets in "light blue” are as energetic as “blue” bullets in "vivid blue", the only difference is the ratio of "blue" to "white" bullets that reaches the retina.


Human Eye
The human eye will respond to wavelengths of light from 390 to 750 10-9 meters (i.e. visible light). To put these lengths into perspective, 10-9 meter is a billionth of a meter.

Human beings can discriminate about 100 different hues. Dogs, on the other hand, have a much more restricted sense of color: they see basically two bands of color groups, namely orange-yellow and blue-violet.

Differences Between Human’s and Dog’s View Of Color.

We see light that is emitted or light that is reflected by objects. For example, we see the moon because the sun’s light is reflected from its surface, which then reaches our retina. Turn off the lights as well as all light emitting sources in a room and we would not be able to see any objects. All objects would appear black to us.

If we see a red cloth, then this implies that the other six components of the visible light have been absorbed by the cloth - except for the red component of visible light. If the cloth is black, then the cloth has absorbed nearly all of the visible or white light and if it is white, then nearly all of the visible or white light has been reflected by the surface. Hence, the color of a cloth or material or textile etc. is dominated by the main wavelengths of visible light that is reflected.

Although color is formulated in the brain, it is the eye that has the receptors that presents to the brain the image that it perceives. There are two sets of receptors in the retina in the back of the eye - rods and cones.

There are about 125 million rods (named because of their shape). They are very sensitive to light but are mostly color blind. They are employed in dim light, which is why the old adage - "all cats are grey in the dark" - was created.

The color detectors in the eye are the cones. There are about 7 million of these in three forms concentrated in the center of vision. Individual cones can only sense one of three narrowly defined frequencies of light: red, green and blue. The response from these three "primary" colors is sorted in the brain in order to give the perception of color. In a "color blind" person one or more of these color receptors is defective and so malfunctions.



Specifying Color
Generally, there ar three terms used to describe and specify color:
(i) Hue: The traditional color name of a specific wavelength of light is a hue. Another description for hue is "spectral" color. All of the colors of the spectrum are hues.
(ii) Value: It is the term used to describe lightness, darkness, tone or shade of a hue. A color is termed "light" in value when it approaches white and "dark" in value, when it approaches a deep color or black.
(iii) Chroma or Saturation: It is the term used to describe depth of color; that is, the dullness, brightness, saturation, intensity, vividness or purity of the color. A bright, intense color is said to have much chroma, whereas a dull color is said to have little chroma. (Note: Chroma is the Greek word for color). A color without any brightness (no hue) is achromatic (black, white and/or grey).

Color Circle. Each hue is opposite its complementary.

The color wheel (right) shows the relationship between hues (around the outside) and saturation or chroma (center to outside). The triangle (left) shows the relationship between value (vertically) and saturation (horizontally).


Colors on Electronic Screens Versus Printed Colors On Paper or Cloth
In color theory, a hue refers to a pure color. The hue of the cloth is modified by undertones of other wavelengths of transmitted visible light that give it an individual shade. The other attributes of “color appearance” centres on: lightness, brightness, colorfulness, saturation and chroma. If colors have the same hue we refer to the colors as “light blue” (lightness) or “vivid blue” (brightness) or “pastel blue” (chroma) to further distinguish between them.

With respect to commercial printers, CMYK is shorthand for cyan (C), magenta (M), yellow (Y) and black (K). The symbol “K” is used to represent black (instead of “B”) since cyan, which is greenish blue, could also claim the symbol “B”.

Colors on the computer or TV screen are specified as RGB (Red, Green or Blue) in two ways. One way is to define a palette (a working set of colors) and assigned numbers to colors on the palette. For example, a bitmap image with 4 bits per pixel can distinguish 24 or 16 colors. The other way is to give values to red, green and blue for each pixel. For example, a 24-bit color uses 8 bits for red plus 8 bits for green plus 8 bits for blue, requiring a total of 24 bits per pixel. Since there are 8 bits used for each color there are 28 or 256 different levels for each of the three colors.
Note: The hexadecimal counting system is used in computer programming to dial up appropriate colors. For example, red with a maximum intensity can be dialled up using the hexadecimal notation of FF0000.

Printed colors on paper are usually specified as CMYK or HSB (hue, saturation and brightness). Because the pigments being mixed are completely different from the phosphor dots on the screen display even after extensive calibrations, what you see on the screen does not necessarily translate to what appears on the paper or cloth. Moreover, hardware limitations make it impossible to print or display all possible colors. Dithering (i.e. representation of an intermediate color by mixing dots or pixels of two other colors) is used to produce shades of grey or colors on a printer or screen that cannot be produced directly.


Color Chemistry
Of course there is a connexion between the chemical structures that make up a surface (such as cloth) and the visible components of colors that are reflected by the surface and those that are absorbed.

Among organic compounds (such as those dyes that are fixed on a surface of a cloth) we find that the colored chemicals usually contain certain groups, which are called chromophores (or color-bearers). These chromophores are usually attached to aromatic rings, such as benzene, or one of the more complex ring structures. Colored molecules have their color intensified or modified by chemical groups called auxochromes. Thus a red dye named alizarin contains two benzene rings (two outside rings marked on the inside by circles of figure below), two carbonyl groups (chromophores – marked as red in in the middle ring of figure below) and two hydroxyl groups (auxochromes – marked as red and white in the right hand ring of figure below). The two carbonyl groups in that chemical structure - when interacting with visible light - are responsible for color, whereas the two hydroxyl groups are responsible for the intensity of the colour.

Chemical structure of Alizarin, and its chromophores and auxochromes.

Color in inorganic compounds (such as lead iodide) is also affected by their electronic arrangement. For example, when lead iodide absorbs components of visible light a transfer of charge occurs in its structure, which is responsible for its golden color.


Color Mixture
Sometimes the eye detects a color that cannot be found in the components of visible light (e.g. grey, brown or purple). To understand this we need to investigate additive and subtractive mixing.

Additive Mixing
Additive mixing has direct relevance with respect to the color of pixels in a TV or a computer screen (see above).

If we have a white screen and we shine a yellow light on it, we will see a yellow spot (since the material that makes up the screen reflects all white or visible light). If we shine a blue-violet light on the same screen we will see a blue-violet spot. If we shine both light beams on exactly the same spot on the screen, what shall we see? The yellow and blue-violet lights are complementary to each other and so their mixture in the right proportions will register as a white spot.

Drawing straight lines through the center spot of the figure below connects other complementary pairs.

Additive Color Mixing Diagram.

Red, blue-violet and green are three of the primary colors. Secondary colors are produced along the sides of the triangle above by mixing any two primaries in different proportion (e.g. mixtures of blue-violet and red light, vary from magenta, to rose pink, as the proportion of red increases). These colors do not occur in the white or visible light spectrum. Mixing across the sides of the triangle in the figure above can make other colors.

Additive mixing of light[4].

If two complementary colors are shone on the same spot, the spot becomes white but it now appears to be a more intense white light. Why is that? Let us say we have aimed 50 yellow bullets and 50 blue-violet bullets at the same spot on the screen. Our retina now perceives 100 bullets, which appears as a more intense "white". The white dot appears more intense than our initial yellow or blue-violet dots due to the total number of light bullets that the retina receives is the addition of both components (i.e. 50 yellow bullets + 50 blue-violet bullets = 100 white bullets received by the retina). This type of mixing is therefore called additive mixing.

Subtractive Mixing
Subtractive mixing is important in the mixing of pigments in a palette and the way dyes work.

If we mix a blue pigment with a yellow pigment we do not get white – we get green. This is because both pigments absorb light. The blue pigment absorbs practically all of the orange and most of the red and yellow wavelengths from white light falling on it. The yellow pigment absorbs almost all of the violet, indigo and the remainder of the red and nearly all of the blue. The seven principal colors of visible or white light are (see above): violet, indigo, blue, green, yellow, orange and red. Hence, the only color not absorbed and reflected into the retina is green.

If both pigments are dull (i.e. absorb strongly) then the green will be even duller. Why is that? Well let us say we have shone on the pigments 16 light bullets of each primary color of white light (112 light bullets in total). With all the absorptions taking place, 96 light bullets have been absorbed and so only 16 light bullets of green light have been reflected. Hence the green light appears duller than the surrounding white light in the room. This process is called subtractive mixing, since all the absorptions that take place reduce or subtract from the initial total number of white light bullets and so the reflected green bullets appear less intense than the initial light (i.e. 112 white bullets - 96 absorbed bullets = 16 green bullets received by the retina).

Mixing blue and yellow are not complementary, but there are complementary colors (e.g. red and green) as shown in the figures below. Mixtures of complementary colors, in right proportions, do not produce white: instead, it produces dark grey. Why is that? Well let us say we shone 112 bullets of white light on both pigments. Then only 16 red bullets return to us from the “red” pigment and 16 green bullets return to us from the green pigment. When we mix these pigments together, in theory a maximum of 32 bullets can return (i.e. 29% of the original total). However, this is even further diminished since some of the “red” pigment in the mixture will absorb some of the green bullets (reducing the total 16 green bullets further) and some of the “green” pigment in the mixture will absorb some of the red bullets (reducing the total 16 red bullets further). Hence far fewer than 32 bullets of light will be returned and so the mixture will appear very dull or tend to the black end of the color scale (note: black is where all bullets have been absorbed and none reflected); that is, the mixed pigment will appear grey to us due to fact that very few light bullets (much less than 32) were returned to our eyes.

White and black are the two extremes: complete reflection produces white (i.e. maximum of the 112 bullets of reflected light reached our eyes); and no reflection but all absorption produces black (i.e. no bullets of reflected light reached our eyes). In between come all shades of grey. A neutral grey reflects all the wavelengths of white light, but it does not reflect enough light to give the full white color.

In the pigment circle (see figure below) a number of pigments are listed. The pigment colors do not correspond to pure colors, but lie between them. If two pigments that are not complementary are mixed, the color produced will lie between them, on the shorter arc of the circle joining them (e.g. red and blue can give violet). If the two pigments are joined by a straight line then the closer the line lies to the center circle the darker the color will be.

Subtractive Color Mixing Diagram.

Subtractive Mixing Of Secondary Light Hues[4].

Since each individual pigment in a mixture subtracts some of the wavelengths and so some of the light bullets falling on the mixture, this type of color mixing is called subtractive mixing. Strictly speaking subtractive mixing can only occur with dyes, which absorb light. On the other hand, pigment particles reflect some light from their surfaces and so mainly subtractive mix but not totally. Subtractive mixing is the type of mixing that the painter must carry out to produce paint with a given color. Today for wall paints, automatic machines carry out this chore.


References:
[1] G.P.A Turner, Introduction To Paint Chemistry And Principles Of Paint Technology, Chapman & Hall, London (1991).

[2] D.A. Downing, M.A. Covington, M.M. Covington, C.A. Covington and S. Covington, Dictionary of Computer and Internet Terms, 10th Edition, Barron’s Educational Series INC. (2009).

[3] Internet reference: https://www.google.com.au/imgres?imgurl=https://etorgerson.files.wordpress.com/2011/04/dogvis.jpg&amp.

[4] P. Lambert, B. Staelelaere, Color and Fiber, Schiffer Publishing Co, West Chester (1986).

[5] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).

1 comment:

Flora Fascinata said...

Huge appreciation for posting this resource! I'll use it to educate myself. x