Glass bottles at Anchor Glass in Shakopee, MN
Molly Bloom
The process that turns sand into glass is very cool – or rather, we should say very hot. Very, very, very hot as it turns out. Humans have been turning minerals from the earth’s crust into glass for 3,500 years. Find out how it’s done and how it’s evolved – from blowing glass by hand to a factory that makes hundreds of glass bottles every minute.
See the glass armonica in action:
The Corning Museum of Glass has a great collection of glass-making demos (see them all here):
Find out more about the FOCI Minnesota Center for Glass Arts.
And check out this glass-making machine at Anchor Glass. It makes hundreds of bottles every MINUTE.
Decoding glass
And have you ever noticed little dots on the bottom of a glass bottle or jar? Those are part of a code that the machines can use to sort the containers quickly. Here’s what the numbers and dots mean:
Decoding glassMolly Bloom
Audio Transcript
Download transcript (PDF)
[PEACEFUL MUSIC] MOLLY BLOOM: You're listening to Brains On from NPR News and Southern California Public Radio. We're serious about being curious. I'm Molly Bloom.
Glass is pretty amazing stuff. It's transparent and strong, beautiful and breakable. It can be used to make windows, bottles, screens, lenses, cups, beakers, aquariums, marbles, beads. It's even making this music.
[PEACEFUL MUSIC]
That's a glass harmonica, an instrument invented by Ben Franklin. It uses rotating glass bowls and water to make music.
Since glass is such a big part of our lives, it makes sense that lots of you have written in with questions about it. 7-year-old Audrey from Cortland, Nebraska asks what a lot of you want to know.
AUDREY: My question is, how do they make glass?
MOLLY BLOOM: The first thing I can tell you about how glass is made, it is hot. Really hot.
BRIA: I'm a heat person, so I like the heat. No, the heat isn't as fun.
MOLLY BLOOM: Bria and her sister Bryn know all about the heat. Bria is into it. And Bryn, not so much. Their friend Eliza agrees.
ELIZA: You just get really tired, and sweaty, and gross really fast. The glass is surprisingly heavy. But once you get used to it, it's not that heavy.
MOLLY BLOOM: I met the three girls at Foci Minnesota Center for Glass Arts. They were learning how to make glass and how to shape it into things like cups and sculptures. When I met them, they were making paperweights.
But why was it so stinking hot in there? Well, it's all because of the ingredients. Glass is made up of minerals mined from the Earth's crust.
The main ingredient is silica sand. And in order to change that sand into glass, it needs to melt. But there's a problem with silica on its own.
KATHRYN WIECZOREK: It has a very high melting point. It's close to 4,000 degrees Fahrenheit. That is really difficult to melt in a furnace.
MOLLY BLOOM: Kathryn Wieczork knows a lot about glass. She's a science educator at the Corning Museum of Glass in New York. She says there's a way to lower the melting point of silica sand.
If you add sodium carbonate, also called soda ash, into the mix, the melting point is lowered to about 2,300 degrees. Still very, very hot. But not quite as hot as 4,000 degrees.
KATHRYN WIECZOREK: The last ingredient is the limestone. So limestone is another mineral that is mined out of the ground. And it has calcium in it. And the calcium helps the sodium and the silica kind of all stay together.
Without the calcium, it would be really unstable. It would be really prone to weathering. And the glass would just kind of deteriorate.
The calcium kind of acts like an emulsifier. So if you've ever made homemade salad dressing, you'll have oil and vinegar. And then you have to add something else because those two things don't want to stick together. So that's kind of what the calcium does.
MOLLY BLOOM: This kind of glass, the kind that's made out of silica, soda ash, and limestone is called soda-lime glass, and is the most prevalent kind of glass made today. It also kind of sounds like a delicious drink, one that would be very refreshing in that hot glass-making environment. So how does a mix of minerals that looks like sand turn into smooth, clear glass? When the silicon dioxide atoms that make up silica sand start out, they have a very uniform crystalline structure.
SUBJECT 1: Molecules, line up.
SUBJECT 2: We're aligned, Sarge.
MOLLY BLOOM: But when we heat it way, up the bonds between the molecules are broken. And the molecules get all jumbled up.
SUBJECT 2: It's hot in here.
SUBJECT 3: It's like a furnace.
SUBJECT 4: I need to go look for some shade.
SUBJECT 5: Get some ice cream
SUBJECT 6: Anyone else want an ice cream?
SUBJECT 1: Get back in line.
SUBJECT 2: Are you kidding? It's way too hot for that. We're just going to go about as we please.
SUBJECT 1: Oh boy, it's hot. You're right. At ease.
SUBJECT 2: Way ahead of you.
SUBJECT 3: I've been lying down for five minutes already.
MOLLY BLOOM: This process is kind of like what happens with ice which melts into water when it heats up. But unlike ice, which goes back to being ice when it cools down, silicon dioxide stays all jumbled.
[WHISTLE BLOWING]
SUBJECT 1: It's starting to cool down. Back in line, molecules.
SUBJECT 2: Are you kidding?
SUBJECT 3: It's way too hot now.
SUBJECT 4: Let's just stay like this. It's not so bad.
SUBJECT 1: I give up.
MOLLY BLOOM: This kind of material where the molecules are all jumbled up is known as an amorphous solid. And once glass has solidified, you can melt it again by applying heat. But it doesn't just go from solid to liquid.
KATHRYN WIECZOREK: Glasses are different. They start to soften. And then as they keep heating up and keep heating up, they begin to flow more and more easily.
And the same thing when they cool down. They go from really flowy, to not as flowy, to rigid. And so it's over a range of hundreds of degrees Fahrenheit that this happens.
MOLLY BLOOM: As Bryn, Bria, and Eliza learned in their glassmaking class, once the molten glass is removed from the furnace, it starts cooling down quickly. So you have to work fast. It becomes too solid to work with when it goes from very, very, very, very, very hot, around 2,700 degrees, to only very, very, very hot, around 1,300 degrees Fahrenheit. But when it's in between those two temperatures, you can work with it and shape it.
ELIZA: Feels like honey
BRYN: I thought I felt like a marshmallow, marshmallow fluff kind of.
BRIA: Yeah, it's like that. When it gets a little harder, when you put your tweezers on to there, it feels like glass. And then when you turn it again, it feels like marshmallows.
MOLLY BLOOM: We're going to find out more about how glass is shaped in just a minute. But first, it's time for the mystery sound.
CREW: Mystery sounds.
MOLLY BLOOM: Here it is.
[CLANKING]
Any guesses? We'll be back with the answer right after this.
[UPBEAT MUSIC]
OK Brains On listeners, you only have a couple more weeks to send in your debate topics for Sanden and Marc. They've hashed out bridges versus tunnels in the past and whether or not cats are evil or just misunderstood. Now they want your help deciding what to debate next, fire or water, carpet or linoleum, squirrels or chipmunks.
Send in your debate topics by Thursday, August 25. We'll narrow down the list. And then you'll get to vote for your favorite.
Now it's time to announce the latest group to be added to the brain's honor roll. These are the kids that keep us going with their questions, mystery sounds, drawings, and high fives.
[LISTING HONOR ROLL]
[TECHNO MUSIC]
(SINGING) These are all [INAUDIBLE].
Now back to that mystery sound. Let's hear it one more time.
[CLANKING]
Any guesses? Here's the answer.
STEWIE: Hi, my name's Stewie.
SILAS: My name's Silas.
STEWIE: Our mystery sound was--
SILAS: --us stirring lemonade in a glass.
CREW: (SINGING) Ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, Brains On.
MOLLY BLOOM: Now back to glass. Where were we? Oh, yeah, where is my random announcer dude? Oh, here it is.
ANNOUNCER: When we last left glass, it was in a molten state. Hot flowing liquid glass in a furnace at nearly 2,700 degrees Fahrenheit. Will it ever cool down? What will become of it? Maybe a tumbler or a window. Only time will tell.
MOLLY BLOOM: Aren't random announcer dudes the best? Anyway, I visited Kyle Fiebelkorn at the Anchor Glass Factory in Shakopee, Minnesota to find out how they turn molten glass into bottles and jars. It starts with a very hot furnace.
KYLE FIEBELKORN: It's hot enough. My one furnace is at 2,860 degrees Fahrenheit on the top side. The other furnace we run about 2,760, 2,770. It's 24/7 operation. I got guys that work around the clock for me. And Christmas is just-- it's just Wednesday.
MOLLY BLOOM: The molten glass inside the furnace is 59 inches deep. That's over 300 tons of molten glass. At the bottom of the furnace under that deep pool of molten glass is what is called a throat. Molten glass goes through that throat to smaller channels that condition the glass, and then send it to machines where it's molded. At this point, the glass has become less liquid.
KYLE FIEBELKORN: Would be kind of like a taffy consistency. Comes out in cylinders. Then we use what are call shear blades to cut that glass cylinder in certain sizes, depending upon what the machine is making, what type of bottle, what size a bottle.
MOLLY BLOOM: Here's some cool bottle-making lingo for you. Those smaller cylinders are called gobs. When the gob is put into a mold, a hole is pressed into the top of the bottle.
That top part of the bottle is known as the finish. Once the gob has the hole pressed into it, it's then known as a parison. Air is then used to blow the parison into the shape of the mold.
KYLE FIEBELKORN: We have what's called the blow-and-blow process. And then you have the press-and-blow process. And then you have narrow-neck press-and-blow process.
MOLLY BLOOM: So sometimes vacuum or plungers are used to help it along. But at its most basic, the shaping of the bottle involves blowing air. Maybe you've heard the term glass blowing. It's a technique that dates all the way back to about the year 50 BC.
KATHRYN WIECZOREK: The Romans realized that they could actually take this glassy molten substance, and put it at the end of a hollow tube, and blow it, and inflate it kind of like a balloon. So that's where glass blowing started.
Before glass blowing, they were making core-formed vessels, which are basically vessels where they would take a stick, and the end of the stick would be covered in a core. And the core was made out of probably clay, maybe some horse manure, and things like that. And they would dip that core into a pot of molten glass, and then let it cool very slowly. And then they would scrape out the core, and they would be left with a tiny little vessel. Maybe can only hold an ounce or two.
MOLLY BLOOM: Humans have been making glass for 3,500 years. But nature has been at it even longer. Take obsidian, for example. It's a black glass made by volcanoes.
KATHRYN WIECZOREK: The volcano gives off lava. And when this lava is cooled very quickly, the atoms don't have time to arrange themselves into nice, orderly patterns. So it cools so quickly that they're left all jumbled.
MOLLY BLOOM: There are also fulgurites. This is glass made by lightning strikes.
KATHRYN WIECZOREK: So basically, lightning will strike a beach. And it melts the sand together really, really fast. And then the lightning goes away. And then the sand cools really quickly. And it forms kind of a glassy structure.
MOLLY BLOOM: And then there are tektites. These are formed by meteor strikes. So in order for glass to be made from raw materials, a lot of heat is necessary. But melting down already-manufactured glass takes far less energy. So glass manufacturers like Anchor like to recycle glass since it makes the process more efficient.
KYLE FIEBELKORN: As much glass as we can get in from the public, well, we'll run it.
MOLLY BLOOM: Recycled glass as well as raw materials help supply their furnace with enough molten glass to feed the bottle and jar making machines. And those machines are hungry.
KYLE FIEBELKORN: We have machines that make 400 bottles every minute.
MOLLY BLOOM: Anchor Glass uses that soda lime mix you heard about earlier. It makes a clear, colorless glass.
KATHRYN WIECZOREK: But we can add different metal oxides to glass to give it different colors. So blue glass is made by adding cobalt oxide to the batch. Green glass is made by adding iron oxide.
MOLLY BLOOM: Manganese makes purple. And adding gold will make glass red.
If you want to see glassmaking in action, the Corning Museum of Glass has live streams of glass-blowing demonstrations. We'll post the link on our website brainson.org. While you're there, you can also see some cool videos of the glassmaking machines in action at Anchor Glass. And you can find out what the code at the bottom of glass bottles and jars means. We'll also post a video of people playing this thing, the glass harmonica.
That's it for this episode of Brains On. Thanks to Sam Chou, Nancy Yang, Meg Martin, Peter Cox, and Phil Piccardi for sharing their vocal talents. Also thanks to Kim [INAUDIBLE] from Anchor Glass and Kelly Nezworski from Foci.
You can send your questions, mystery sounds, and high fives any time. Just email them to brainson@M, as in Minnesota, PR.org. Thanks for listening.
[PEACEFUL MUSIC]
Glass is pretty amazing stuff. It's transparent and strong, beautiful and breakable. It can be used to make windows, bottles, screens, lenses, cups, beakers, aquariums, marbles, beads. It's even making this music.
[PEACEFUL MUSIC]
That's a glass harmonica, an instrument invented by Ben Franklin. It uses rotating glass bowls and water to make music.
Since glass is such a big part of our lives, it makes sense that lots of you have written in with questions about it. 7-year-old Audrey from Cortland, Nebraska asks what a lot of you want to know.
AUDREY: My question is, how do they make glass?
MOLLY BLOOM: The first thing I can tell you about how glass is made, it is hot. Really hot.
BRIA: I'm a heat person, so I like the heat. No, the heat isn't as fun.
MOLLY BLOOM: Bria and her sister Bryn know all about the heat. Bria is into it. And Bryn, not so much. Their friend Eliza agrees.
ELIZA: You just get really tired, and sweaty, and gross really fast. The glass is surprisingly heavy. But once you get used to it, it's not that heavy.
MOLLY BLOOM: I met the three girls at Foci Minnesota Center for Glass Arts. They were learning how to make glass and how to shape it into things like cups and sculptures. When I met them, they were making paperweights.
But why was it so stinking hot in there? Well, it's all because of the ingredients. Glass is made up of minerals mined from the Earth's crust.
The main ingredient is silica sand. And in order to change that sand into glass, it needs to melt. But there's a problem with silica on its own.
KATHRYN WIECZOREK: It has a very high melting point. It's close to 4,000 degrees Fahrenheit. That is really difficult to melt in a furnace.
MOLLY BLOOM: Kathryn Wieczork knows a lot about glass. She's a science educator at the Corning Museum of Glass in New York. She says there's a way to lower the melting point of silica sand.
If you add sodium carbonate, also called soda ash, into the mix, the melting point is lowered to about 2,300 degrees. Still very, very hot. But not quite as hot as 4,000 degrees.
KATHRYN WIECZOREK: The last ingredient is the limestone. So limestone is another mineral that is mined out of the ground. And it has calcium in it. And the calcium helps the sodium and the silica kind of all stay together.
Without the calcium, it would be really unstable. It would be really prone to weathering. And the glass would just kind of deteriorate.
The calcium kind of acts like an emulsifier. So if you've ever made homemade salad dressing, you'll have oil and vinegar. And then you have to add something else because those two things don't want to stick together. So that's kind of what the calcium does.
MOLLY BLOOM: This kind of glass, the kind that's made out of silica, soda ash, and limestone is called soda-lime glass, and is the most prevalent kind of glass made today. It also kind of sounds like a delicious drink, one that would be very refreshing in that hot glass-making environment. So how does a mix of minerals that looks like sand turn into smooth, clear glass? When the silicon dioxide atoms that make up silica sand start out, they have a very uniform crystalline structure.
SUBJECT 1: Molecules, line up.
SUBJECT 2: We're aligned, Sarge.
MOLLY BLOOM: But when we heat it way, up the bonds between the molecules are broken. And the molecules get all jumbled up.
SUBJECT 2: It's hot in here.
SUBJECT 3: It's like a furnace.
SUBJECT 4: I need to go look for some shade.
SUBJECT 5: Get some ice cream
SUBJECT 6: Anyone else want an ice cream?
SUBJECT 1: Get back in line.
SUBJECT 2: Are you kidding? It's way too hot for that. We're just going to go about as we please.
SUBJECT 1: Oh boy, it's hot. You're right. At ease.
SUBJECT 2: Way ahead of you.
SUBJECT 3: I've been lying down for five minutes already.
MOLLY BLOOM: This process is kind of like what happens with ice which melts into water when it heats up. But unlike ice, which goes back to being ice when it cools down, silicon dioxide stays all jumbled.
[WHISTLE BLOWING]
SUBJECT 1: It's starting to cool down. Back in line, molecules.
SUBJECT 2: Are you kidding?
SUBJECT 3: It's way too hot now.
SUBJECT 4: Let's just stay like this. It's not so bad.
SUBJECT 1: I give up.
MOLLY BLOOM: This kind of material where the molecules are all jumbled up is known as an amorphous solid. And once glass has solidified, you can melt it again by applying heat. But it doesn't just go from solid to liquid.
KATHRYN WIECZOREK: Glasses are different. They start to soften. And then as they keep heating up and keep heating up, they begin to flow more and more easily.
And the same thing when they cool down. They go from really flowy, to not as flowy, to rigid. And so it's over a range of hundreds of degrees Fahrenheit that this happens.
MOLLY BLOOM: As Bryn, Bria, and Eliza learned in their glassmaking class, once the molten glass is removed from the furnace, it starts cooling down quickly. So you have to work fast. It becomes too solid to work with when it goes from very, very, very, very, very hot, around 2,700 degrees, to only very, very, very hot, around 1,300 degrees Fahrenheit. But when it's in between those two temperatures, you can work with it and shape it.
ELIZA: Feels like honey
BRYN: I thought I felt like a marshmallow, marshmallow fluff kind of.
BRIA: Yeah, it's like that. When it gets a little harder, when you put your tweezers on to there, it feels like glass. And then when you turn it again, it feels like marshmallows.
MOLLY BLOOM: We're going to find out more about how glass is shaped in just a minute. But first, it's time for the mystery sound.
CREW: Mystery sounds.
MOLLY BLOOM: Here it is.
[CLANKING]
Any guesses? We'll be back with the answer right after this.
[UPBEAT MUSIC]
OK Brains On listeners, you only have a couple more weeks to send in your debate topics for Sanden and Marc. They've hashed out bridges versus tunnels in the past and whether or not cats are evil or just misunderstood. Now they want your help deciding what to debate next, fire or water, carpet or linoleum, squirrels or chipmunks.
Send in your debate topics by Thursday, August 25. We'll narrow down the list. And then you'll get to vote for your favorite.
Now it's time to announce the latest group to be added to the brain's honor roll. These are the kids that keep us going with their questions, mystery sounds, drawings, and high fives.
[LISTING HONOR ROLL]
[TECHNO MUSIC]
(SINGING) These are all [INAUDIBLE].
Now back to that mystery sound. Let's hear it one more time.
[CLANKING]
Any guesses? Here's the answer.
STEWIE: Hi, my name's Stewie.
SILAS: My name's Silas.
STEWIE: Our mystery sound was--
SILAS: --us stirring lemonade in a glass.
CREW: (SINGING) Ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, Brains On.
MOLLY BLOOM: Now back to glass. Where were we? Oh, yeah, where is my random announcer dude? Oh, here it is.
ANNOUNCER: When we last left glass, it was in a molten state. Hot flowing liquid glass in a furnace at nearly 2,700 degrees Fahrenheit. Will it ever cool down? What will become of it? Maybe a tumbler or a window. Only time will tell.
MOLLY BLOOM: Aren't random announcer dudes the best? Anyway, I visited Kyle Fiebelkorn at the Anchor Glass Factory in Shakopee, Minnesota to find out how they turn molten glass into bottles and jars. It starts with a very hot furnace.
KYLE FIEBELKORN: It's hot enough. My one furnace is at 2,860 degrees Fahrenheit on the top side. The other furnace we run about 2,760, 2,770. It's 24/7 operation. I got guys that work around the clock for me. And Christmas is just-- it's just Wednesday.
MOLLY BLOOM: The molten glass inside the furnace is 59 inches deep. That's over 300 tons of molten glass. At the bottom of the furnace under that deep pool of molten glass is what is called a throat. Molten glass goes through that throat to smaller channels that condition the glass, and then send it to machines where it's molded. At this point, the glass has become less liquid.
KYLE FIEBELKORN: Would be kind of like a taffy consistency. Comes out in cylinders. Then we use what are call shear blades to cut that glass cylinder in certain sizes, depending upon what the machine is making, what type of bottle, what size a bottle.
MOLLY BLOOM: Here's some cool bottle-making lingo for you. Those smaller cylinders are called gobs. When the gob is put into a mold, a hole is pressed into the top of the bottle.
That top part of the bottle is known as the finish. Once the gob has the hole pressed into it, it's then known as a parison. Air is then used to blow the parison into the shape of the mold.
KYLE FIEBELKORN: We have what's called the blow-and-blow process. And then you have the press-and-blow process. And then you have narrow-neck press-and-blow process.
MOLLY BLOOM: So sometimes vacuum or plungers are used to help it along. But at its most basic, the shaping of the bottle involves blowing air. Maybe you've heard the term glass blowing. It's a technique that dates all the way back to about the year 50 BC.
KATHRYN WIECZOREK: The Romans realized that they could actually take this glassy molten substance, and put it at the end of a hollow tube, and blow it, and inflate it kind of like a balloon. So that's where glass blowing started.
Before glass blowing, they were making core-formed vessels, which are basically vessels where they would take a stick, and the end of the stick would be covered in a core. And the core was made out of probably clay, maybe some horse manure, and things like that. And they would dip that core into a pot of molten glass, and then let it cool very slowly. And then they would scrape out the core, and they would be left with a tiny little vessel. Maybe can only hold an ounce or two.
MOLLY BLOOM: Humans have been making glass for 3,500 years. But nature has been at it even longer. Take obsidian, for example. It's a black glass made by volcanoes.
KATHRYN WIECZOREK: The volcano gives off lava. And when this lava is cooled very quickly, the atoms don't have time to arrange themselves into nice, orderly patterns. So it cools so quickly that they're left all jumbled.
MOLLY BLOOM: There are also fulgurites. This is glass made by lightning strikes.
KATHRYN WIECZOREK: So basically, lightning will strike a beach. And it melts the sand together really, really fast. And then the lightning goes away. And then the sand cools really quickly. And it forms kind of a glassy structure.
MOLLY BLOOM: And then there are tektites. These are formed by meteor strikes. So in order for glass to be made from raw materials, a lot of heat is necessary. But melting down already-manufactured glass takes far less energy. So glass manufacturers like Anchor like to recycle glass since it makes the process more efficient.
KYLE FIEBELKORN: As much glass as we can get in from the public, well, we'll run it.
MOLLY BLOOM: Recycled glass as well as raw materials help supply their furnace with enough molten glass to feed the bottle and jar making machines. And those machines are hungry.
KYLE FIEBELKORN: We have machines that make 400 bottles every minute.
MOLLY BLOOM: Anchor Glass uses that soda lime mix you heard about earlier. It makes a clear, colorless glass.
KATHRYN WIECZOREK: But we can add different metal oxides to glass to give it different colors. So blue glass is made by adding cobalt oxide to the batch. Green glass is made by adding iron oxide.
MOLLY BLOOM: Manganese makes purple. And adding gold will make glass red.
If you want to see glassmaking in action, the Corning Museum of Glass has live streams of glass-blowing demonstrations. We'll post the link on our website brainson.org. While you're there, you can also see some cool videos of the glassmaking machines in action at Anchor Glass. And you can find out what the code at the bottom of glass bottles and jars means. We'll also post a video of people playing this thing, the glass harmonica.
That's it for this episode of Brains On. Thanks to Sam Chou, Nancy Yang, Meg Martin, Peter Cox, and Phil Piccardi for sharing their vocal talents. Also thanks to Kim [INAUDIBLE] from Anchor Glass and Kelly Nezworski from Foci.
You can send your questions, mystery sounds, and high fives any time. Just email them to brainson@M, as in Minnesota, PR.org. Thanks for listening.
[PEACEFUL MUSIC]
Transcription services provided by 3Play Media.
