Learning Objectives
- Learn the basic properties of light and how light is perceived as color
- Learn the basics of color theory
- Learn the basic molecular structure of a reactive dye molecule
- Learn how an alkali catalyst works to help form a covalent bond between the dye & fiber
- Use fiber reactive dyes to conduct a color mixing experiment & chemical reaction on a t-shirt with tie-dye
- Dharma Tie-Dye Big or Little Group Kit
- 100% Cotton Clothing / Fabric to dye
- Markers
- Household items (zip lock bags, etc)
- CMY Color Wheel
Words to Know
- wavelength
- electromagnetic
- spectrum
- additive color
- subtractive
- hydrogen bond
- hydroxyl group
- cellulose
- color
- hue
- saturation
- value
- alkali
- catalyst
- chromophore
- covalent bond
What is Color and What does it have to do with light?
Color is an effect produced by the eye and its nerves by light waves of different wavelength or frequency. Light transmitted from an object to the eye stimulates the different color cones of the retina, making possible perception of various colors in the object.
Since the colors that compose sunlight or white light have different wavelengths, the speed at which they travel through a medium such as glass differs; red light, which has the longest wavelength, travels faster through glass than blue light, which has a shorter wavelength.
When white light passes through a glass prism, it is separated into a band of colors called a spectrum. The colors of the visible spectrum are usually called red, orange, yellow, green, blue, indigo, and violet. The phrase ROY-G-BIV is an easy way to remember this. This same effect happens when light goes through water droplets or rain causing us to see a rainbow.
Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum labeled "visible light." This “visible light" corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range of violet through red. The human eye is not capable of “seeing" radiation with wavelengths outside the visible spectrum (see figure B).
The Color of Objects
Color is a property of light that depends on wavelength. When light falls on an object, some of it is absorbed and some is reflected. The apparent color of an opaque object depends on the wavelength of the light that it reflects; e.g., a red object observed in daylight appears red because it reflects only the waves producing red light. The color of a transparent object is determined by the wavelength of the light transmitted by it. An opaque object that reflects all wavelengths appears white; one that absorbs all wavelengths appears black. Black and white are not generally considered true colors; black is said to result from the absence of color, and white from the presence of all colors mixed together.
Additive Color
Colors whose beams of light in various combinations can produce any of the color sensations are called primary, or spectral, colors. The process of combining these colors is said to be additive: the sensations produced by different wavelengths of light are added together. The additive primaries of light are are red, green, and blue-violet. White can be produced by combining all three primary colors. Any two colors whose light together produces white are called complementary colors, e.g., yellow and blue-violet, or red and blue-green.
Subtractive Color
When pigments or dyes are mixed, the resulting sensations differ from those of the transmitted primary colors. The process in this case is “subtractive," since the pigments subtract or absorb some of the wavelengths of light. With transparent dyes, like our Fiber Reactive Dyes that we use for Tie-Dye, Cyan (blue-green), Magenta (red-violet), and Yellow and are called subtractive primaries, or primary colors. This is called the CMY system, and you use a CMY color wheel. (With more opaque pigmented products, like our fabric paints, use traditional Red, Yellow and Blue as primaries and use a Red, Yellow, Blue color wheel.) A mixture of cyan and yellow pigments yields green, the only color not absorbed by one pigment or the other. A mixture of the three primary pigments produces black. These subtractive primary colors are the ones we use when dyeing, and the Fiber Reactive Dye equivalents are Turquoise, Fuchsia, and Lemon Yellow.
Properties of Color
The scientific description of color, or colorimetry, includes all of the relevant properties of a color subjectively and objectively. The subjective description includes the hue, saturation, and lightness or brightness of a color.
HUE refers to what is commonly called color, i.e., red, green, blue-green, orange, etc.
SATURATION refers to the richness of a hue as compared to a gray of the same brightness; this is also known as chroma.
VALUE measures the brightness of an opaque object on a scale from dim to bright or from black to white.
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