When Blue Makes White

“Have you ever heard the term Blue Hairs?”

Michael Woudenberg

, my co-author from another mother who writes

Polymathic Being

asked me. It’s another one of those typically random observations where lots of things come together to create an interesting problem, and that’s why we’re talking about it.

Growing up in South Carolina, I had heard the term occasionally from my dad, when he kindly but humorously referred to a group of older women. I told Michael the phrase was familiar to me.

“Do you know why they were called that?”

I didn’t. Instantly, I was curious. Michael explained:

Well, when I first moved to Tucson Arizona. I heard the term and it made no sense to me. Someone told me it was because their hair was so thin you could see the blue of the sky.

I kind of forgot about it until over a decade later when I was reading Farmer Boy by Laura Ingalls Wilder and they mentioned using bluing compound to clean and I had no idea what that was.

So I Googled it and found that’s how you make whites whiter. So for the blue hairs it dates back to when smoking was more ubiquitous and the elderly, with white hair, would find it yellowing with the smoke. To make it nice and white they’d wash their hair with bluing and sometimes overdo it.

As an art major—painting, in fact—I feel I can speak with some authority on the subject of mixing colors. I’ve never heard of adding blue paint to make anything whiter. Curious!

But we aren’t mixing the colors. This is where the science of bluing crosses the physics of light, the biology of our eyes, and the psychology of how we see. To better explain this interesting twist we’ll use the ubiquitous case of clothing.

It turns out that the concept of using blue pigments to enhance the color white has been around for thousands of years. The ancient Egyptians used natural blue dyes like indigo to make their fabrics appear brighter. This is because, when clothing ages, it tends to yellow over time. Natural body oils and sweat can soak into fabrics and react with oxygen, leaving behind yellow stains.

If the clothes were stored in humid conditions, the oxidation process would accelerate, leading to even more yellowing. Exposure to the sun could break down fibers, and washing the clothing with iron-rich water—like, say, the Nile River—left stains behind.

Over the ensuing millennia, other cultures used similar approaches, with notable improvements in the 16th century with the invention of smalt—tiny bits of ground-up blue glass. Smalt and indigo remained the twin pillars of bluing until the discovery of synthetic ultramarine in 1826.

Wait. How can yellow be eliminated by the addition of the color blue in fabric dying and laundry?

First off, Bluing doesn't actually remove any of the yellowing. If you recall Color Theory 101, yellow and blue are on the opposite side of the RGB color wheel.

Adding a tiny touch of blue counteracts the yellow tones, making fabric appear whiter and brighter.

We see color because of the way objects reflect light. White objects reflect nearly all wavelengths of visible light, while colored objects absorb certain wavelengths and reflect others. That’s the physics of light but that’s not enough to make things look whiter.

Enter biology and psychology. Essentially, our brains are tricked by wavelengths: yellow fabrics reflect more yellow light, while blue pigment absorbs those same yellow wavelengths. The combination of blue reflected light and the fabric's original reflected light creates a different signal pattern for our cones, which we perceive as white.

Now that you know that blue makes this appear whiter, take a look at everything you use to wash around the house, even swimming pool clarifiers, and see just how many use a blue dye because it counteracts yellowing that can persistently make things look dingier.

Just don’t overdo it like those sweet elderly folk who turned their white hair into blue hair and created a nickname that has lasted throughout history.

If you’ve enjoyed the way our two brains interact, check out Becoming Polymathic, An Ode to Coffee, and An Ode to Beer once you’re done here. And, be sure to check out

Polymathic Being

if you have the bandwidth for another newsletter! I (Andrew) read or listen to every one of Michael’s essays over there.