chemistry has always played a big role in art and culture.

Just take colors for example!

But what is a color really?

And what led to the use of some colors in the first place?

Let's trace a color back to its roots. And leaves.

One color story started with this plant, called Indigofera tinctoria or Indigo.

It's native to India and the name comes from the Greek work indicon,

meaning Indian substance.

Substance?

In this plant there is a colorless molecule that looks like this.

But under some conditions, this molecule can react and change,

looking like this instead.

So what's the big deal then you say?

In chemistry, rearranging the molecular structure like this

can be like night and day, or in this case like green and blue.

Because this last molecule is blue.

After its discovery, people now wanted the blue indigo molecule,

especially for dying clothes.

But this is where it gets a little tricky.

You see, this blue indigo molecule is insoluble,

meaning the blue dye simply won't stick.

We now know that to overcome this, the solution that the dye is in has to have a high pH.

Well, people did still figure this out a long time ago.

So what did people have a few thousand years ago to raise the pH?

Did you know that urine becomes basic over time?

What is believed to have happened is that leaves from the indigo plant

got accidentally soaked in urine.

So if a textile came in contact with the basic urine-indigo solution

it turned blue!

So the high pH actually helped the molecules stick to the fabric.

But wait a minute...

How can this molecule be colorless and this be blue?

Hey Louise, can you take it from here?

On it!

When we look at the two molecules again, we can see that the blue molecule is larger

and has a greater number of double and single bonds.

It is this molecular structure that ultimately makes us see the colors.

But first we need light.

Light contains wavelengths of all colors.

If something is black, all the colors from the light are absorbed

and none is reflected back to our eyes.

We therefore see the object as black.

Now if we look at something colorful,

we see the red color because the flower reflects back the red wavelengths and absorbs others.

And the reason the flower absorbs particular colors comes down to its chemical structures.

So these alternating double and single bonds are the reason the indigo molecule is blue.

And if certain atoms are added to the molecule the absorbed wavelengths can change,

and that makes us see a different color.

The discovery of indigo color was huge for ancient art and culture.

And by understanding the chemistry behind it we can now synthesize the same molecule that

was for so long extracted from this plant.

And the use of indigo is still booming,

in fact we use about 13 000 metric tonnes every year.

And if we weren't synthesizing the molecule,

we would have needed about 3.9 billion kilograms of plants per year.

By the way, you might even be wearing some of it right now.

So we've learned that the colors,

that have an important role in art and culture, have some interesting chemistry histories to tell.

And the reason we see colors in the first place comes down to the structure of the molecules.

And just by changing the molecular structure slightly we can even change the color we see.

And here's a challenge.

Can you think of any other colors that have come from plants or animals?

And remember,

Chemistry is all around you!