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                                                                                                                   Molecular Spectroscopy Project:


1: History        2:Importance and Usage        3: Spectroscopy        4: Current Studies        5: Future Expts.

6: HS Classroom Lesson:        A: Lesson Plan        B: Worksheets        C: Instructor Guide

1. History and Introduction

    Fluorescent whitening agents (FWAs), also known as optical brighteners or brightening agents, are the dyes responsible for making clothes (and a host of other things) appear whiter and brighter.  To fully understand how FWAs have become so inextricably integrated into the life of the average person in the U.S., it may be helpful to take a look at one of the original product that FWAs replaced.

Bluing, FWAs Precursor

Figure 1. Mrs. Stewart's
Bluing (1).

bluing    Bluing, a mild blue dye, was the precursor to FWAs (2).  Before FWA use became ubiquitous, bluing was used by homemakers to make white laundry whiter (See Figure 1).  Aged persons could also use it to make their greying hair appear less yellow (3).

    Of course, sometimes mistakes were made.  Too much bluing could result in bluish-tinged laundry or hair.  In fact, the overuse of bluing hair dye amongst appearance-concerned, elderly women may have given rise to the phrase "little, old, blue-haired lady."  Reference to this physical trait even shows up in the famous Christmas rhyme by Randy Brooks, "Grandma Got Run Over By a Reindeer (4): "
  "Now the goose is on the table,/ And the pudding made of fig, ahh,/ And the blue and silver candles/ That would just have matched the hair in Grandma's wig."

How Does Bluing Work?

Figure 2. The perception of the color yellow (5).
yellow object    An object that reflects all light without absorbing any of it appears white, and an object that absorbs all light without reflecting any appears black.  A yellow object (such as stained laundry or discolored white hair) appears yellow by absorbing blue light and reflecting the remaining light.  Figure 2 shows how the selective absorption and reflection of light by an object results in the perception of yellow color.

Figure 3. Additive color mixing shows how when
yellow and blue light are mixed, they
result in
white light (6).

additive mixing of light    By applying bluing, the originally yellow object would simultaneously absorb some yellow light and reflect blue light, effectively cancelling out the disproportionate absorption of blue light.  An object would appear less yellow because near equal amounts of yellow and blue light would be absorbed and reflected, resulting in the perception of a whiter color.  Figure 3 shows how mixing equal amounts of yellow and blue light results in the color white.

    It is important to note that bluing would make laundry (and hair) appear whiter in color, but not brighter.  The perception of brightness is related to the amount of light reflected, and the application of bluing would not increase the amount of reflected light, but would rather decrease it.  If too mich bluing were added, linens could even take on a slightly bluish, rather than bright white, appearance.

The Beginning of FWA Use
    Fluorescent whitening agents work in a somewhat similar manner to bluing, but present a clear improvement because they not only increase the perception of whiteness, they also increase brightness.  FWAs could whiten yellow or discolored fabrics, but they also had wider applicability because of their ability to increase the total amount of reflected or emitted light for any object (7).  This is why FWAs are also accurately called optical brighteners or fluorescent brightening agents and are now found in a wider range of products than bluing ever could be.

    The first use of FWA in textiles occured in 1929, and they started being used extensively in commercial textiles around 1940 (8).  Since then, they have been incorporated into laundry detergents, plastics, and paper products (9).  The following section, Section 2, examines their widespread importance and usage in industrial and consumer products in more detail before Section 3 explains the spectroscopic properties that give FWAs their superior whitening and brightening properties.  Click on the arrow button at the right to go to the next section.

  1. Image of Mrs. Stewart's Bluing. http://www.amazon.com/Mrs-Stewarts-Bluing-8oz/dp/B000PB5ZQ8 (April 1, 2009).
  2. Old and Interesting: "Laundry blue: Bluing, Reckitt's blue, dolly blue, washing whitening." http://www.oldandinteresting.com/laundry-blue.aspx (April 1, 2009).
  3. Mrs. Stewart's Bluing: Other uses. http://www.mrsstewart.com/pages/otheruses.htm (January 7, 2009).
  4. TV Tropes: Elderly blue-haired lady. http://tvtropes.org/pmwiki/pmwiki.php/Main/ElderlyBlueHairedLady (April 1, 2009).
  5. Image explaining the perception of the color yellow according to color theory. http://personal.uncc.edu/lagaro/cwg/color/intro_color.html (April 1, 2009).
  6. Image of additive color mixing. http://www.d.umn.edu/~mharvey/th1501color.html (January 7, 2009).
  7. Maseka, K. (2005). The emission and absorption of radiation by white and dye cotton fabrics laundered with fluorescent brightening agents. AATCC Review, 5(10), 35-38.
  8. Science Tech Entrepeneur, July 2006 (2006). http://www.techno-preneur.net/information-desk/sciencetech-magazine/2006/july06/Fluorescent_brighteners.pdf  (January 7, 2009).
  9. P.V.A. (1997). Fluorescent brighteners. Chemical Market Reporter, 251(4), SR21.