What makes paint stick?

DAKARI: You're listening to Brains On, where we're serious about being curious.

VIOLET: Brains On is supported in part by a grant from the National Science Foundation.

[MUSIC PLAYING]

MOLLY BLOOM: That paint on your wall--

AIDAN BAY: Or on a firetruck.

MOLLY BLOOM: Or a park bench.

AIDAN BAY: It's stuck there.

MOLLY BLOOM: You could get it off, but it wouldn't be that easy.

AIDAN BAY: Today we're asking how. How does paint stick?

MOLLY BLOOM: We'll find out right now.

AIDAN BAY: Keep listening.

MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly Bloom, and my co-host today is 11-year-old Aidan Bay from Los Angeles. Hi, Aidan.

AIDAN BAY: Hi, Molly.

MOLLY BLOOM: Aidan, you are a painter. And what kind of paint do you like to use?

AIDAN BAY: Acrylics. Water-based paints.

MOLLY BLOOM: And how long have you been painting for?

AIDAN BAY: As far as I can remember. I think since preschool, which was four or five, maybe even younger.

MOLLY BLOOM: And what kind of subjects do you like to paint?

AIDAN BAY: I like sports. I do sports players, like baseball players and football players. But then I also like doing things like robots, because I think they're really cool looking. And it's really fun to do it with paint.

MOLLY BLOOM: For people who haven't painted before, how does it start? How do you first start your paintings?

AIDAN BAY: Well, I've done this-- started this not too long ago. But how I start is I get this one thing called gesso. It's like this white paint. And you put it onto the canvas before, so it becomes really nice and smooth. And then when the paint comes on, it comes on a lot easier. So that's how I start.

MOLLY BLOOM: And then do you sketch first with a pencil?

AIDAN BAY: Yeah, I sketch with a pencil. Sometimes I do it freely and I just start with paint, maybe. But usually I'll do it with pencil. And then I paint it with the colors I want. And then I'll keep on doing more layers, because the first layer, it's probably not going to come on as smoothly as maybe you want it to go.

MOLLY BLOOM: So the painting is made up of many layers of paint.

AIDAN BAY: Yes. It's not just one. Sometimes it may, but not really.

MOLLY BLOOM: So people who look at paintings, they might just see a painting and they might have no idea how many layers went into it.

AIDAN BAY: For some people, they're probably not even-- if they didn't know paintings, they'd probably think that they just put on one layer of paint.

MOLLY BLOOM: Aidan, do you mix your own paints?

AIDAN BAY: Yeah. I have this one chart. And actually, you know multiplication tables?

MOLLY BLOOM: Uh-huh.

AIDAN BAY: There's a big chart and then it shows you. Well, it's like that. You have to get two colors, like these base colors, and I have them all. And then you have to think of the color you want. The strokes, what two colors you need to mix it.

MOLLY BLOOM: That's really cool. So if you want to make some green color, you would need a yellow and a blue, for instance?

AIDAN BAY: That's the base. But also, you might put-- you might get a regular green. You can add a little bit of white if you want it lighter. And some people think you might need black to make it darker, but it sometimes can be-- it's goopy. So stick around maybe a gray or a brownish.

MOLLY BLOOM: Do you ever think of painting as science or a math because of the adding and subtracting and the mixing that you're doing?

AIDAN BAY: Not really. Because I like painting because it's really stress free. It gets complicated that sometimes. But then I think after a while, I've been painting for a while, so it's got really easy.

AUDIO TRACK: Brains On!

MOLLY BLOOM: Aidan knows a lot about painting, and we heard from another painter. Eight-year-old Sadie from Oakland. She emailed us with a question.

SADIE: What makes paint stick? I thought it was a good question because I don't know, and I don't know if many people do. And I just really want to know. I think it's probably a material in the paint. But I don't know what material.

MOLLY BLOOM: To find out how paint sticks, we're going to start by zooming in, way in, to learn more about what paint and really everything else is made of. Our pal Jackie is going to take it from here.

JACKIE: Have you heard of atoms before? They're kind of a big deal. Even though they're very tiny. Like a million times smaller than the width of a human hair. Pretty much everything on Earth is made up of atoms. You, me, everything. Now, some atoms like to link up with other atoms to form bigger things called molecules. Like how a few smaller LEGO pieces go together to make a bigger LEGO piece.

For paint to stick, the atoms that make up the paint molecules have to interact with the atoms that make up the wall molecules. So how do atoms and molecules interact with each other? To find out, let's visit a molecule party.

[PARTY MUSIC]

PARTY: Molecule party!

ATOM: Hey, H2O. I haven't seen you since the pool. How's it going?

H2O: Oh, just floating by.

ATOM: Oh, here you go.

JACKIE: Much like friends hanging out, atoms like to interact. It's how they link together to form molecules. But they interact for different reasons. Sometimes it's because these atoms share something in common, called an electron. These are tiny negatively charged particles that spin around the atom. Atoms really like electrons. If they get just the right amount, they feel balanced and right with the world.

Take these two atoms over here, for instance.

ATOM: Hey, cool electrons you got there.

ATOM: Yeah, I got a bunch. Actually, they're pretty nifty.

ATOM: I've only got a few. It's not as fun. I wish I had more.

ATOM: Yeah. Hey! Hey, wait a minute. Why don't we share some of mine? Then it'll be like we both have a ton.

ATOM: Whoa, you'd do that for me? Bro, we are going to be the best friends.

JACKIE: When atoms share electrons like this, it's called a covalent bond. Those are very hard interactions to break up. Sometimes atoms don't just share, though. They straight up give away their electrons. This can happen when a negatively charged atom and a positively charged atom interact to make a molecule. These two atoms are really attracted to each other the same way the positive side of one magnet is drawn to the negative side of another.

Take this couple, for instance.

ATOM: This is so fun. I just love parties.

ATOM: Sheesh, parties are lame.

ATOM: Seriously? What's not to love? There's pizza, there's soda.

ATOM: I prefer salads and sparkling water.

ATOM: You don't like talking to friends?

ATOM: Rather be reading books.

ATOM: Dancing?

ATOM: I'm sitting.

ATOM: Games?

ATOM: Meditation.

ATOM: Hanging out late?

ATOM: Getting up early.

ATOM: Dogs?

ATOM: Cats.

ATOM: Sunshine?

ATOM: Rain clouds.

ATOM: You are--

the most fascinating person I have ever met. I think I'm in love.

ATOM: Me, too. I've never met someone so different, and yet, I just can't get enough of your positive attitude.

ATOM: I want you to have something.

ATOM: What is it?

ATOM: Here. Open it.

ATOM: Electrons? I've never felt so balanced. You're good to have around.

JACKIE: Isn't that sweet? They're bonding to form a molecule. When one atom gives electrons to another like this, they form what's called an ionic bond.

DJ: Ionic in the house say yeah.

CROWD: Yeah!

DJ: Covalent in the house say, yeah.

CROWD: Now!

JACKIE: Now, ionic and covalent bonds usually help to form molecules. These are the bonds that allow certain atoms to link up to become paint molecules. So once you've got your paint molecules, how do they stick to the wall molecules? Well, this takes a different kind of interaction, one that's not so intense.

Like over here. We have a group of friend atoms sitting on one side of a table. They're chatting with a different friend group on the other side of the table.

ATOM: Oh my gosh,

[CHATTING]

JACKIE: Now, at any given moment, one friend might be really interested in what someone on the other side of the table is saying.

ATOM: So once we were bonded, I mean, nothing could break us up. Until water came along.

ATOM: Wait, wait, what? Water enters the picture? Tell me more.

JACKIE: But that interest may only last a few seconds before that atoms attention drifts.

ATOM: Well, water used to be my best friend. But then, things got a little crazy and then water wasn't really my best friend.

ATOM: Speaking of water, I'm thirsty. Maybe I should go get a drink.

JACKIE: But before that friend can leave, his pal to the right might suddenly get really interested in what someone else across the table is saying.

ATOM: Hey, dude, you hear the story carbon is telling? It's so funny. Check it out.

ATOM: What? Tell it to me.

ATOM: Well, I'm like one of the key building blocks of all life on Earth.

JACKIE: In this case, no one atom at the table is strongly interacting with any other one for very long. But as a group, they stay put because at any given moment, a few of them are interested enough to keep talking. On an atomic level, this kind of interaction happens because those atoms sometimes have very brief moments where one side becomes positive or negative. As we mentioned earlier, positive atoms like to stick around electronegative atoms.

So for this ultra short period, an atom might be attracted to another atom, but only for that instant before it goes back to feeling neutral. If it happens enough times dispersed across enough atoms, things stick. See?

ATOM: Hey, should we get going?

ATOM: Nah, let's sit here and talk a while longer. I wanted to ask that atom over there about valence.

ATOM: Oh. No, that sounds cool. OK, I'm down to stick around.

JACKIE: This kind of interaction is called a dispersion force. It's an example of an intermolecular bond that's weaker than covalent or ionic bonds. But it's just as important. Paint usually sticks to things thanks to these weaker intermolecular bonds. So next time you brush on some paint, imagine the paint molecules sitting at a table with the wall molecules chatting. They'll keep the conversation going, and that'll keep the paint stuck to the wall.

[PARTY MUSIC]

DJ: Y'all ready to spell with me? Somebody say B.

CROWD: B!

DJ: O.

CROWD: O.

DJ: N.

CROWD: N.

DJ: D.

CROWD: D.

DJ: B-O-N-D. B-O-N-D. Say it with me. Molecule party, yeah! Molecule party.

MOLLY BLOOM: Now we're going to zoom out a little more and find out what ingredients make up paint.

AIDAN BAY: To find out, we talked to someone who knows a lot about paint.

RICH SIMON: My name is Rich Simon.

MOLLY BLOOM: Rich is a chemist who works at Valspar.

AIDAN BAY: They make paint.

MOLLY BLOOM: And Rich's job is all about solving paint mysteries. To start off, he told us paint is made up of four parts.

AIDAN BAY: Pigment, which is the color.

MOLLY BLOOM: Solvent, which is the liquid.

AIDAN BAY: Resin, which carries the pigment.

MOLLY BLOOM: And additives. Now paints go through a transformation when they go from being wet to dry.

AIDAN BAY: The solvent for most paints is water.

MOLLY BLOOM: And the resin can be something like latex. When you look at a latex molecule, it looks like a long chain bonded together. Those kinds of molecules are called polymers.

RICH SIMON: What's happening in that situation is your water is evaporating off. Your polymer are in-- you can think about it as little beads that are floating around inside the water. We would use the term dispersed. And as the water is evaporating off, your beads start to come together. You want those beads not only to stick together, but you want them to start forming together. All that water is evaporating off is you want those polymers, those molecules, to start entwining with each other.

MOLLY BLOOM: So as the water evaporates, those beads of resin spread out and create a thin film of paint over the surface. It's that film that's left behind that ends up being the paint we see on a surface.

AIDAN BAY: But not every paint likes every surface. A paint that is perfect for wood might not stick to metal, and vice versa.

RICH SIMON: So you really have to engineer or modify your paints in such a way that's specific for your surface that you want. So if they didn't like going to that surface and they weren't interacting with that surface, you would just be able to pull it off like a sheet of paper.

AIDAN BAY: At Valspar, where Rich works, they make all kinds of paints.

MOLLY BLOOM: From beige wall paint.

AIDAN BAY: To green tractor paint.

MOLLY BLOOM: To a purple grape soda can.

AIDAN BAY: Rich's lab helps figure out which paint will stick to which surface.

MOLLY BLOOM: If someone is trying to make a new paint and it's not working, Rich will figure out why it's not.

RICH SIMON: We're the problem solvers. The ones who have the high tech equipment to be able to understand what is happening in a paint system. Everything that happens is because of changes that are happening at this microscopic and molecular level that we can't see, but we have instrumentation to be able to help us understand.

[VOCALIZING]

AUDIO TRACK: Brains On.

MOLLY BLOOM: And now Aidan, before we go any further, we have some important business to take care of. It's time for the mystery sound.

[MYSTERY SOUND CUE]

AUDIO TRACK: Mystery Sound.

MOLLY BLOOM: Are you ready? Here it is.

[RUBBING SOUND]

Do you have any guesses?

AIDAN BAY: It sounds like a jet from a plane engine. How it starts. And also, it sounds like the waves from the ocean.

MOLLY BLOOM: And did you hear that little noise that was like a swishing noise, like a-- over top of that?

AIDAN BAY: Yeah, sort of.

MOLLY BLOOM: While you think about it, we're going to come back to it in a little bit and we'll hear it again.

AIDAN BAY: OK.

MOLLY BLOOM: And you can see if you have any other guesses.

AIDAN BAY: All right.

[MUSIC PLAYING]

MOLLY BLOOM: Right now, we're working on a series of episodes all about the science of cooking. And we want to hear from you. If aliens landed and it was your job to introduce them to the food of planet Earth, what dish would you serve them, and why? Send your ideas to hello@brainson.org.

You can also send your mystery sounds, drawings, and questions to that same email address. That's what Aisha did.

AISHA: My question is, how does the sand get on the beach?

MOLLY BLOOM: We'll have an answer to that question during our Moment of Um at the end of the show. That's also when we'll read the latest group of listeners to be added to the Brains Honor Roll. Those are the brilliant minds that keep us going by sharing their ideas with us. Stick around.

So glad you stuck around, because we're about to talk to someone who uses paint that doesn't come from a lab.

AIDAN BAY: James Griffith lives in Los Angeles, California. He paints animals using a very special medium.

MOLLY BLOOM: We won't ruin the surprise. Let's let James tell us about it himself. Welcome to Brains On.

JAMES GRIFFITH: Good to be here.

AIDAN BAY: So what do you use for paint?

JAMES GRIFFITH: Well, I use tar. And I get the tar at the La Brea Tar Pits.

MOLLY BLOOM: For those of us not in Los Angeles, what are the La Brea Tar Pits?

JAMES GRIFFITH: The La Brea Tar Pits is a magical place. Right in the middle of Los Angeles is a portal to the ancient past. And it's a big hole in the ground. And in that hole bubbles out this tar from an underground lake. A reserve of tar that's been there for millions of years. And that tar is famous because over those millions of years, various animals that have once lived and now are extinct got trapped into that tar. And as a result, it has one of the largest warehouses, if you will, of ancient bones of animals that no longer exist.

AIDAN BAY: Do you use tar, do you add things to it, or you just use plain tar?

JAMES GRIFFITH: Well, if I use tar straight from the Tar Pits, it would stay sticky for millions of years. And that could be a real problem if anybody wanted to keep the painting for very long or didn't want to have things stick to it.

AIDAN BAY: Right.

JAMES GRIFFITH: So I add a lot to it. It's an alchemy of chemicals. But as you probably are aware of how paint is made, there's a lot of chemicals that can go into paint to make it work and stay dry.

AIDAN BAY: Do you paint on wood, canvas, paper?

JAMES GRIFFITH: The tar is fairly acidic. And what that means is that if you were to put it on a fabric or paper, it would eventually cause the paper to rot. So I have to put it on a neutral medium that will be easy to preserve. So I use metal. And I spray it with a primer, and then I put gesso on top so it's white. And then I paint with a tar in very thin layers. And so far, the years I've been doing this, it hasn't broken down yet.

MOLLY BLOOM: Well.

[CHUCKLES]

JAMES GRIFFITH: Tar is dark and it's fairly brown even when you thin it down. And so my paintings look like they're made with coffee. And I thought, I need some more color in here. So I hike a lot. I go off in the wilderness, so to speak, and nature. And I'm always looking around at the materials around me to see, what else could I stick in a painting?

Pollen is one thing. It's yellow. And so I collect pollen in the right season. And sometimes I mix that with chemicals to be like a paint. But sometimes I simply sprinkle it on the paint when it's wet, the tar paint. I use sometimes minerals. Old rocks and things. If I see a bright red rock in Utah, I might pick it up and see if I can grind it into a powder and make paint out of it.

MOLLY BLOOM: Whoa.

AIDAN BAY: Yeah, I saw some blue in some of your paintings.

JAMES GRIFFITH: Yeah. That's copper sulfate. And it makes a beautiful blue. The trouble with working with that is it has a dangerous side to it. It's poison. But it can be handled carefully. And it's beautiful, beautiful blue.

MOLLY BLOOM: And if kids were interested in making their own paint out of natural materials, is there somewhere you would recommend they start?

JAMES GRIFFITH: You can make paint in many simple ways by just taking acrylic varnish that you can buy in a store, an art store. And just add stuff to it. You could add sand that you find in the playground. You could add glitter that you buy in a store. But you can just start sticking stuff in paint, and it'll dry. And essentially, that is paint.

MOLLY BLOOM: Thanks so much for being here today, James.

JAMES GRIFFITH: My pleasure. Good to meet you.

AIDAN BAY: Head to our website, brainson.org, find out more about James Griffin's paintings.

[MUSIC PLAYING]

We know you're curious. What questions do you want to see answered on Brains On? Send them to us.

MOLLY BLOOM: You can email them to hello@brainson.org.

AIDAN BAY: If you're a Brains On superfan, help us out by leaving a review on iTunes. The more reviews we have, the easier it is for other kids and parents to find us.

MOLLY BLOOM: It's quick and easy, and you can tell the world there while you listen to Brains On. Thanks.

Ears open, brains on. Let's go back to the mystery sound. Here it is.

[RUBBING SOUND]

Any final guesses?

AIDAN BAY: It sounds like a brush going like on a canvas or some type of surface really quickly.

MOLLY BLOOM: You are so very close. Here is the answer.

KRISTY JEFFCOAT: That was the sound of using a cotton swab to clean a painting.

MOLLY BLOOM: That's Kristy Jeffcoat. She's a painting conservator at the Midwest art Conservation Center in Minneapolis. She helps restore paintings that have been damaged or have deteriorated over time.

KRISTY JEFFCOAT: As soon as the paint is applied onto the surface, it starts deteriorating, actually. It starts aging, just like people do. When a painting comes into the lab, the first thing we do is what we call an examination. As is the case with this painting, it had a very yellow oxidized varnish on top. The traditional varnishes while in the beginning give it a very nice saturated, beautiful gloss look on the surface, yellow over time. And that was the case with this one.

And then also, there was just a lot of retouch. So somebody had tried to clean it at some point in its life. And in doing so, overcleaned it. Removed some original paint. And they covered all those spots up that they had overcleaned with a new paint. And so as a conservator, one thing that we do, we don't become the artist. We never cover up original paint.

MOLLY BLOOM: Kristy works with really old paint. Some of it is up to 600 years old. But what do you think the future of paint is?

AIDAN BAY: I think there's a lot of paint still and it's baby steps. I think it's going to get a lot more advanced.

MOLLY BLOOM: So what would you like to see paint be able to do that it can't do now?

AIDAN BAY: I think change colors would be awesome. But I think that's pretty far in the future. I think I can just think of a color I want it to be. And then when it comes on, it will be the exact same color I want. And also, the paint never really runs out on your brush. One dip could last an entire canvas. That'd be really cool.

MOLLY BLOOM: That would be really cool. Maybe someone will invent that one day.

[MUSIC PLAYING]

The explanation of why paint sticks is complicated.

AIDAN BAY: It has to do with what the paint is made of.

MOLLY BLOOM: Solvent, resin, pigment, and additives.

AIDAN BAY: And how it dries.

MOLLY BLOOM: The solvent evaporates.

AIDAN BAY: And the molecules the paint and surface are made of.

MOLLY BLOOM: And how they bond together. That's it for this episode of Brains On.

AIDAN BAY: This episode was produced by Sanden Totten, Marc Sanchez, and Molly Bloom.

MOLLY BLOOM: Many thanks to Keith Bey, Remi Emdor, Rich Simon, Colin Turner, Francisco Zeira, Steven Hobbs, Chelsea Martinez, and Colin Campbell. And thanks to our molecule actors, Jackie Fuller, Eric Wringham, Meg Martin, Curtis Gilbert, and Tom Weber.

AIDAN BAY: To hear more episodes, head to our website.

MOLLY BLOOM: brainson.org. While you're there, you can subscribe to our newsletter to find out about new episodes and other fun stuff.

AIDAN BAY: And you can always subscribe in your favorite podcast app. And if you are on iTunes, leave us a review. We'll be really, really, really grateful.

MOLLY BLOOM: Totally find us on Facebook and follow us on Instagram and Twitter at @brains_on. Or you can email us at hello@brainson.org. Now, before we go, it's time for our Moment of Um.

AUDIO TRACK: Uh. Um. Um. Um. Um. Um. Um.

AISHA: Hi, my name is Aisha. I live in Marietta, Georgia. I'm six years old. My question is, how does the sand get on the beach?

SAM GREENAWAY: Well, I'm Sam Greenaway. I'm a Lieutenant Commander with NOAA. And I run the technology program at the [INAUDIBLE] in the National Ocean Service. My field's mapping, so I go and map the ocean.

Sand on beaches comes from mountains, comes from ground up rocks. They get washed down into the ocean. And then get moved around by currents and waves and sometimes fetch up on beaches.

Sometimes there's bits of shell in there. That obviously comes from bits of living animals. Sometimes bits of ground up coral. Sometimes different kind of rock, depending on what kind of rocks are in the area. Black sand usually comes from volcanic rocks. Light colored sand are largely quartz. And if you pick up a handful of it, they even look clear.

I've even been to some beaches where the sand squeaks quite loudly when you watch over it. A lot of the white sand beaches on from, say, Hawaii are bits of ground up coral. And that coral gets ground up by a fish, a parrotfish that chews on reefs, and poop it out as nice ground up white sand. And that washes up on beaches. I'd encourage anybody next time they're at a beach to just grab a handful and have a close look.

MOLLY BLOOM: No time to relax on a sandy beach right now because I need to read this list of listeners who are going to be added to the Brains Honor Roll. These are the magnificent minds who have shared ideas, questions, mystery sounds, and drawings with us. It's true. Thousands of minds are better than one.

[MUSIC PLAYING]

[LISTING HONOR ROLL]

AUDIO TRACK: Brains Honor Roll. High fives.

MOLLY BLOOM: We'll be back soon with more answers to your questions.

AIDAN BAY: Thanks for listening.

[VOCALIZING]

AUDIO TRACK: Brains On.

ATOM: Come on the dance floor.

ATOM: Molecule party.

ATOM: Party, party, party.

[LAUGHS]