Category: Chemistry—Chemical Changes
Project Idea by: Clay Hooper and Megan Witcher
A dye is a substance used for changing the color of other things such as fabrics. Dyes contain a colorant, which is a substance that selectively absorbs and reflects visible light so that you see a certain color.
Visible light is light the human eye can see. White light is a combination of all light colors in the visible spectrum, which in order from least to most energy are red, yellow, orange, green, blue, indigo, and violet. When white light strikes cloth that is dyed red, the red colorant absorbs all of the colors in the light except red, which is reflected. This reflected light enters your eye, and you perceive the cloth as being red in color.
The colors in some dyed materials fade (become lighter in color) when exposed to sunlight or through washing. Colorfastness is a measure of how well a dyed material resists fading. A dyed material that resists fading is said to have greater colorfastness. Colorfastness of a dye can be improved by using a substance called a mordant. A mordant is a chemical that bonds the colorant in a dye to a material. This happens because part of a mordant particle bonds to a particle in the material and another part of the mordant particle bonds to a dye molecule.
Mordants include alum, cream of tartar, and table salt. In some dyeing procedures, the material is soaked in a solution made by mixing a mordant with water, then the material is placed in a dye solution. A project question might be, "What effect does the concentration of a mordant have on the colorfastness of a natural dye?"
Clues for Your Investigation
Select a mordant and prepare four or more solutions with different concentrations of the mordant and distilled water. Place 4 or more pieces of white cotton fabric in each of the mordant solutions for a measured amount of time. Then place each piece of fabric in a selected dye, which might be a food dye such as blackberry juice or another dark-colored juice. For a control, place fabric that has not been treated with the mordant in the dye. Rinse the fabric in distilled water to remove excess dye. Dry, then test for colorfastness. For example, you might place the fabric pieces in sunlight for a measured amount of time. Whatever your method of testing colorfastness, keep one piece of fabric from each test out of the light for comparison in order to determine the degree of color change.
Independent Variable: Concentration of mordant
Dependent Variable: Colorfastness of dye measured by degree of fading
Controlled Variables: Type of dye and mordant, distilled water, color and type of fabric, time of soaking in the mordant and dye, temperature of soaking solutions, method of washing, time of fabric testing, method of measuring the degree of color of fabric
Control: Fabric not treated with mordant
Other Questions to Explore
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