Purple shampoo can often feel shrouded in mystery.
How is it even possible that a bottle filled with violet suds can make blonde hair feel so much fresher and brighter without bleach? What are the secrets of purple shampoo, and how does it make blonde hair go from drab to fab?
Keep reading, and all your questions will be answered!
Purple shampoo is a type of shampoo that was formulated to contain teeny-tiny molecules of purple dye. When purple dye (in particular, Ext Violet #2), interacts with a yellow-y head of blonde hair, the result is a more ashy, less chicken-yellow shade of blonde.
Think of it as an at-home toning system to help you hide brassy undertones in blonde hair. The effects are temporary, so regular usage of purple shampoo is a must in order to see results.
If you're familiar with color theory, you'll know that purple and yellow are complementary colors. This means that they are directly opposite from one another on the color wheel.
When complementary colors are combined in equal proportions, they effectively cancel each other out.
If you mix a pure purple with a pure yellow in completely equal amounts, the result will be neither purple nor yellow, but a dark grey or ashy-brown color. A different effect is created when complementary colors are combined in unequal proportions. If you mix a lot of pure yellow with a little bit of pure purple, you'll get a less intense yellow. Similarly, if you mix a lot of pure purple with a little bit of pure yellow, you'll get a less intense purple.
Using this logic, you can start to understand how purple shampoo works its magic on yellow-blonde hair. When a little purple dye is combined with a lot of yellow hair, the saturation of the yellow is decreased, leaving a more desirable ashy hue as the final result.
Purple shampoo can't actually lighten your hair. However, it can create an illusion of brightness.
Confused? Let's back it up.
Because it does not contain an ingredient that will chemically change the color of your hair, purple shampoo cannot truly lighten hair. If anything, purple shampoo may make your hair temporarily slightly darker.
This is because the inky purple pigments found in purple shampoo are a darker color than the shades of yellow in blonde hair. Even when a very small amount of purple shampoo is applied to blonde hair, the result will likely be at least a little bit darker than before.
Think about it this way; if you've ever drawn on a piece of paper with a yellow colored pencil, the result is pretty light right? Now, If you color over that yellow with a purple pencil, no matter how light the purple may be, the end result will be darker than the yellow you started with. Feel free to test this out for yourself at home to see for yourself!
The brightening effect caused by purple shampoo is actually illusionary and happens because of an effect called bluing. While your hair might be very slightly darker than before, it will not look darker, because of the ways our eyes perceive color.
This is pretty complicated, so let's use an example.
If you've purchased a bleach-free laundry product to whiten white clothes, you're probably more familiar with this phenomenon than you may think. Like grey or blonde hair, white clothing can acquire a yellowy color after continuous use. Yellowing causes the crisp, cold white of clothing to become warmer, and appear darker and more used.
By adding trace amounts of fluorescent blue colors to detergents, laundry products are able to re-introduce a cool tone to these fabrics, and make them appear lighter, colder, and less yellow, which translates to looking fresher and newer.
As humans, we have learned to associate certain yellowy warm tones (such as the faded yellow color of old white clothing) on certain surfaces (like hair or fabric) with environmental grime, sweat, and general icky-ness. We generally perceive these colors as being more undesirable and less fresh.
When cooling hues are added to mask these warm tones, the result feels fresher to the eye, and therefore brighter and more desirable. The less warm, the better we think it is.
Who knew that your hair and your laundry had so much in common, right?
As we've established, purple shampoo is a pretty complicated aspect of cosmetic chemistry and should be formulated by the best experts available. Check out our hair quiz, and have a chemist make an affordable purple shampoo just for you!
The Formulate Team