You might be old enough to remember the days when mom got the laundry clean with a combination of detergent and chlorine bleach. Those were the days when we used to separate whites from colors so that the bleach wouldn’t damage the colors and the dyes from colored fabrics wouldn’t leech into the whites. A lot has changed since then.
One thing that has not changed is our obsession with clean, white clothing. Who among us wants our whites to look dingy gray? None of us, which is why we continue to use special laundry detergents and non-chlorine bleaches to keep our whites white. But that leads to a question: is white really just an optical illusion?
That very question was raised by Wall Street Journal contributor Helen Czerski in a May 24 piece prompted by her taking in a cricket match. She wondered to herself how the players’ white uniforms retained their brilliance despite cricket being played on natural grass.
How We Perceive White
Before we get into Czerski’s explanation, it is important to understand how the human eye perceives white. White is actually not a color. The perception of light occurs when all the visible wavelengths of the spectrum reflect off a single surface. There are seven colors in the spectrum the human eye normally sees. Remember ROYGBIV?
When a piece of white clothing is stained green by grass, for example, it is because some of the pigment from the grass has penetrated the fabric. That pigment causes some of the other wavelengths to be absorbed. Green is still reflected, so green is what we see.
So how is this an optical illusion? It’s not. The optical illusion comes into play when that same white uniform is laundered. The stain and its pigment aren’t removed. They are masked by one of two tricks launderers figured long ago.
Color Disruption and Color Balance
Alsco, a national provider of uniform rentals based in Salt Lake City, says commercial laundries have a variety of products they can use to ‘remove’ stains from white clothing. All sorts of detergents, bleaches, and even enzyme-based products do the job nicely. But as Czerski explained in her piece, all those products do one of two things: either disrupt color or balance it.
Certain stains show up more visibly in white fabric because their pigments absorb some of the light energy at the blue end of the spectrum. Color disruption works by rearranging the molecules so as to interrupt their absorption capabilities. If they cannot absorb those wavelengths, the stain will have seemingly disappeared.
The concept of color balance is similar. However, its source is drastically different. Color balancing relies on light from the ultraviolet spectrum that the human eye cannot see. Just like white fabrics, laundry detergents contain what are known as optical brighteners. These brighteners absorb ultraviolet light and some of its associated heat, then release a lower energy light that is blue.
Our eyes can see what is happening. Yet this extra blue light balances out the rest of the colors being reflected so that pigments toward the blue end of the spectrum cannot be seen. Have you ever noticed how a white T-shirt glows when exposed to black light? That’s because you’re seeing all that extra blue light produced by the optical whiteners.
It turns out that those white uniforms are just an optical illusion. Bleaches and optical brighteners don’t actually remove stains, they just make them impossible to see. In the end it doesn’t matter. White looks good no matter how you produce it.