SYSK Selects: How Mirrors Work

Whether using polished metal surfaces or clear glass, human beings have enjoyed admiring their reflections for centuries. In this episode, Josh and Chuck reflect on the types, mind-melting physics, superstitions and rather interesting history of mirrors.

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Episode Transcript

Speaker 1 (00:01):
Good afternoon, and welcome to Stuff you Should Know Selects.
It is Charles W. Chuck Bryant here in. My pick
for this week is How Mirrors Work from September fourteen,
two thousand ten. And boy, this one was a tough one.
I remember when we had the idea of doing a
show on mirrors. I thought, well, that's going to be
short and not so interesting. But then I thought, oh,

(00:21):
wait a minute, how do mirrors work? How are those
things made? Where did they come from? It's pretty amazing.
So we get into all that and more, and it's
a pretty fascinating episode. And this will be one where
you can kind of whip out some of these facts
at your next dinner party and amazing to light your
friends and family. So enjoy How Mirrors Work right here,

(00:42):
right now. Welcome to Stuff you Should Know from House
Stuff Works dot com. Hey, and welcome to the podcast.

(01:03):
I'm Josh Clark, there's Charles W. Chuck Bryant. We're about
to talk about mirrors. I set up it's a sinct
how are you were you in the mirrors growing up?
Now that we said, you know, I did it scinctly,
we're gonna just blow like three minutes right. No, I
was asking you if you were into mirrors, in the
mirrors growing up? Yeah, I mean that didn't every kid

(01:25):
go through a phase where they're like very obsessed with
their looks and mirrors and things. Oh yeah, I was
into myself. I wasn't in the mirrors. They were just
a means and end, you know. Yeah, But I like
I was reading this and I kind of was just
thinking myself and remembering laughing about I remember being like
fifteen and like stopping to look at mirrors anytime there
was one to what looked like Yeah, and now I

(01:46):
just I break them. I'd forgotten all about that phase
of my life though, until you just brought it up.
Remember that. Yeah, it's nice to be able to not
look at a mirror. Like some days I'll go out,
you know, after getting ready in the morning, and I
have no idea what I actually look like. But I'm
so And this is um this cross pollination with an
earlier podcast. I suffered from body dysmorphic disorder so badly

(02:10):
that I don't really know what I look like anyway.
What do you think you look like? I think I
look a bit like the top from Taxidermia. I what's
that it's not plusant? Okay, well you don't my friend.
I don't even know what he looks like, but I
can tell you don't look like him. I appreciate that, Chuck, Chuck,
do you want to hear what I had in store? Like?

(02:32):
I could not come up with an intro for this.
Let's hear it. Websters defines mirror. I'm kidding. I always
going to say something equally bad, though, It's going to
be something along the lines with mirrors are ubiquitous. I've
seen at least six of them today. They weren't always
that way, though, Chuck. Well, it says in the article

(02:53):
here the full length mirrors have only been around four years.
That didn't seem right. That's not right. No, um full
length mirrors. There is a type of full length mirror
um that has been around for about four years. Full
length mirrors, as far as I know, are mirrors capable
of reflecting a full image of a person, have been

(03:13):
around since about the first century A d actually um
and mirrors us using surfaces polished surfaces to see our
own reflection. Um has been around since about six thousand BC. Yeah,
the earliest ones were found in Anatolia, Turkey and they're

(03:33):
polished subsidian. Yeah, it's a volcanic glass. Yeah, so it's
it's dark, this interesting, but it's still produced the best reflection,
I guess at the time. At the time, yeah, I
mean you gotta you gotta go with what you what
we have to work with, right. Well yeah, but then
after that they led them to um like silver and
bronze and copper, polished polished reflections basically, And Chuck, I

(03:54):
don't know if you've ever held a hunk of of
copper or bronze I haven't, or silver I have. Okay,
it's heavy, Yeah, it's real heavy. Right. So this actually
limited the size of mirrors for centuries, right Yeah. And
they were just kind of decorative at first, two right,
I think so. And you also had to be extremely rich,

(04:15):
um to own one of these, right, um. And then
around I think the Middle Ages, we became capable of
making glass, and all of a sudden, it was like
mirror technology just takes a huge leap forward. Well true,
but not not super uh forward, because the sand was
pretty impure back then they used to make the glass.

(04:37):
So I think they, um they said in the article,
was until like the Renaissance that it kind of really
started becoming a little more polished, if you will, terrible.
And then the Venetians are who really you know with
a glass and everything. They just they just took in
ran with it. Well. Even still, if you successfully made
a mirror UM, it was probably extremely expensive as well

(04:59):
because they were so rare. The process of manufacturing a
mirror UM very infrequently produced a usable mirror. That's what
you're doing was adhering um melted molten metal onto glass,
which almost always broke the glass. So when it didn't,
I'm sure you're just like, oh my god's the first

(05:21):
one in seven years? Right? Um? But that when I
was reading this article, I didn't really think about it.
That's what a mirror is, isn't it. I've even seen
the back of mirrors and been like others like metal
looks like spray painted on the back. That's exactly right.
And that was a process um what's it called silver
ring that was invented by a guy named Justice von

(05:43):
Liebig and in eighteen thirty five, if he figured out
how to spray very thin layer of silver um or
aluminum on the back or on one side of a
glass and they're my friend. You have the modern mirror. Yeah,
and now that I think they make it now by
heating aluminum in a vacuum in kind of much the

(06:04):
same way or different methods, but the same same concept.
Go ahead, Well, I wanted to say when when you
were talking about the Renaissance, the Venetians were they, I
guess they had the secret of mirrors under wraps like
the Mason's very much so. Um. And if you were
a mirror maker and it got out that you had

(06:27):
told someone how to make mirrors, you were frequently killed, right, yeah,
trade secret. But when mirrors were introduced, um, when good
mirrors were introduced, not polished subsidian, things changed a little bit,
especially with art. Right Yeah, I never really considered that,
but that it spawned something that would become a hallmark
of the art world, which is the self portrait. Right

(06:49):
before that, you couldn't draw yourself because you could not
see yourself. That's exactly right, And you could, but I
mean you're gonna use like maybe a pond or well,
piece of polished medal or something like that. Imagine like
going out and looking at a pond and going back
and sitting down that I was opposed to having a
mirror there. Yes, really simplified it. It's also not coincidental
that UM good mirrors came about at the same time

(07:12):
that UM linear perspective was introduced into art. What. Yeah,
there's a guy named um Filippo Brunus Bruno LLESHI nice, Chuck,
thank you for doing that, UM, and he he I
guess discovered linear perspective because I think it's one of
the things that was always there. We just stumbled upon

(07:33):
it through mirrors. That's how we figured it out. Yeah,
because if you look at a mirror, all of a sudden,
linear perspective really comes into focus, right you will. Well.
And then scientists UM said hey, we could use these
to make like reflecting telescopes, and that was what year
was at. That was a long time ago. The first
reflecting telescope was invented by a guy named James Bradley

(07:56):
just off the top of my head. Very well done. Uh,
And the mirrors were also used by a very very
famous scientist early scientists named Archimedes. Supposedly, Yeah, I wrote
an article on archimedes death. Ray. Oh did you write that? Yeah?
Did you ever read it? I did back in a
while ago. Just out of interest, how about that? Thanks
a lot man. Sure did you see in it? Um?

(08:17):
Some I can't remember. It was one of the Ivy
League schools. They tried to set things on fire with
this system of mirrors. That archie, that's who it was,
and they succeeded. Yes, And the MythBusters claimed it was busted,
like they set a small fire. But I think they
busted it because they said it wasn't enough to like
sink a ship. But m I T I mean, they

(08:39):
caused quite a fire on that boat, and of course
they had. I mean I saw this set up online today.
It was pretty massive. I don't know if Archimedes had
that kind of technology or at least that many mirrors
at its disposal, or maybe he did, and plus they
had I think they used pretty good mirrors too. Yeah,
well it was legend though. They don't know if the
Archimedes sing is true. Right. We know that he invented

(08:59):
the water screw and let's save countless lives. What's that
It's a way to deliver water from the ground top side.
Oh really yeah cool? You have to check it out,
smart dude. Um so chuck, We now know the comprehensive
broad strokes of the history of mirrors. Right, Yes, let's
talk about mirror physics. We work for how Stuff Works

(09:22):
dot com, which means we're pretty much obligated to discuss
the physics of whatever we're talking about any time it applies, right,
And that's true, and mirrors are definitely one of those times. Yes,
So Chuck take it away. Well, I can cover the
first part because it makes sense to me. The law
of reflection um Josh says that when you bounce array
of light off the surface, it bounces back off in

(09:43):
a certain way, and it is um the angle of
incidences is when it comes in the angle of reflection.
It when it bounces off, and it matches so that
the way they pointed out in the article, which makes
sense to me, is like at sunset, the sun is
very low on the horizon, so it bounces off at
a low angle, or approaches the water at a low angle,
like at a lake. Let's say, then it bounces off

(10:05):
of that lake at the same low angle, like right
into your face. Right, But if it seems brighter, if
the sun's overhead though, the sunlight is coming down under
the lake and it's reflecting back up basically over your head.
You're looking at a horizontal angle pretty much, and this
is happening on a vertical angle. Yeah, that's why you'll

(10:26):
get like more glare at a sunrise or a sunset scenario. Um.
And what you're saying, the angle of incidence equals the
angle of reflection. Right. Indeed, if you take if a
if a beam of light is shot at a ninety
degree angle or no, let's say eighty degree angle, it's
going to bounce off at an opposite eighty degree angle.
So both are at eighty degrees. But if you look

(10:48):
at the whole thing, the incidents and the reflection, it's
going to cover a hundred and sixty degrees right right,

(11:19):
all right, So that's the first part. That's that's how
that explains how light reacts with with reflection, and that's
where the smooth surface with with most things like say,
look at my hand man, Take a look at these hands, um,
the the light that's bouncing off of them. What's giving
us the ability to see these huge, awesome hands, um,

(11:41):
is they're not huge. Are they are smaller than average size? No,
they're they're bigger than mine. I got small hands. I
wouldn't see you have small hands. Let's see now those
are like, those are totally normal. I don't have hair
on the back of my hands either. I've got hair
in my first knuckles. Yeah, Robin Williams. Um, what's allowing
us to see our hands right now and judge their

(12:03):
size and scale is, um, what's called diffuse reflection. Which
the light that's coming off of all of these light
bulbs right now are hitting all these different areas, these
different services on my hands, and it's bouncing off, it's
being scattered right the mirror with the highly reflective surface. Um,
what we have is called specular reflection. And that is

(12:26):
where it's pretty close to the law of reflection, where
the angles coming in at one or the lights coming
in at one angle and coming off the at the
same degree in the opposite direction. Right, Um, Which is
why we're allowed to see ourselves in a piece of
glass with metal on the back. And what this creates

(12:48):
when you're looking at yourself is called the virtual image. Right.
I find it fascinating. Yeah, me too, And it's a
little brain melty for me, of course. But at the
same time you realize, like, well, you've grown up around
mirrors the whole time, and no one has any real
concept of of how they work. Right, We just take
for granted that they do work, but you don't really

(13:10):
give much thought to how they're working. Right, Like the
Venus effect. Did you read about that? Yeah, that that's
explained that because this is where when we talk about
Actually the Venus effect is two different things, and both
of them kind of melt my brain. That the left
and right being reversed, which is not actually true, and
then the venus effects. So let's talk about both of those. Okay, Well,

(13:30):
the Venus effect is basically just shows how little we
can grasp or how little we grasp mirrors and how
they work. If you look at paintings of the Venus
de Milo, Venus the goddess um almost always she's holding
a hand mirror, and in the painting you can see
her face in the mirror, but she's looking at herself
in the mirror, and her face is painted in the

(13:53):
mirror for the benefit of the viewer. But you take
for granted that she's viewing herself, when in actuality, if
you could see Venus is in the mirror, she wouldn't
be able to see herself she'd see you in the
mirror because of the angle or the law of reflection. Yeah,
and that's the only way I finally understood that was
when I remembered, like in my film set Days, when
you shoot a person looking in a mirror, they aren't

(14:16):
They don't see themselves in the mirror, clearly, because you
would see the camera behind them so that the mirror
is angled, and it looks like they're looking at themselves
and primping, but they're not seeing themselves. Pretty cool, right,
So that makes sense to me now it does, isn't it. Yeah? Okay,
the other thing you were saying is left and right, Yeah,
it's not actually left and right. Yeah, this one was
a little brain melty, but I think I finally got

(14:36):
it too. Okay, So consider that what you're not, what
you're seeing isn't actually your reflection, but another version of
yourself in the mirror world. Right. If you look at
it that way, then the mirror represents the halfway point.
It's always halfway between you and your virtual self, right, right,
Because your virtual self, that image of yourself in the

(14:57):
mirror is always twice as it's always two times away
from you. With the mirror representing the halfway point right,
So your two feet from the mirror, and your virtual
self is another two feet away from you. Right, You
see what I'm saying. Yeah, And the left and right
thing isn't really left and right, it's really front and
back that are reversed. You again, think of yourself as

(15:17):
the virtual image you walk into the mirror world, you
take you go another two feet away from where you're
just standing, so you're now for your four feet away
from where you're just standing and turn around right, Which
is weird because it actually gives the virtual image something
of its own identity, doesn't it does. It's a little creepy. Yeah,
So when you're looking at a mirror, you're it's not
a reflection of you from the mirrors perspective. It's like that.

(15:41):
The one example they gave was if you wrote something
on a piece of paper and then held that paper
up to the light and looked at it from the back,
it would appear backwards. But it's not right. You're just
behind it, yes, man, isn't it. Yeah? It's pretty interesting stuff.
And I gotta say when you two things, when you
mentioned doing mirrors, I said to myself, really, And then

(16:01):
when we told Jerry what we were doing this on.
She was like, really, yeah, but it's I think it's
much more interesting than I originally thought. Well again, it's
like the butterfly swings, you know, like we just have
to know that if we're gonna understand absolutely everything that's
going on in the world, which is our mission. Yes. Uh,
should we talk about curved mirrors now? Yeah, because we
were talking about virtual images, there's actually a way to

(16:23):
project a real image where this thing isn't in the mirror.
It's outside of the mirror, but it's not really there.
It's a projected image and that uses, um, concave mirrors.
You might be familiar with holograms, right, is that the
same concept there? He uses concave mirrors. And actually, if
you want to see a really cool example of a

(16:44):
hologram produced by a set of concave and flat mirrors, um,
you should type in mirrage in YouTube and look for
the one that's a lowercase just mirrage And it's a
little piggy um And it's pretty cool the demonstration that
this guy does. Yeah, I'll check that out. But Chuck,
there's concave and convex, right, yeah, convex is the one

(17:05):
that curves outward and it reflects at a wider angle
near the edges in the center, So things are actually
smaller and you can cover more areas. So that's why
they'll use those. Uh, they'll stick them on like your
passenger mirrors, so you can see more area around your car.
And it also notes you know, objects are smaller than
they appear or closer than they appear. Objects are smaller

(17:26):
than the appear. But they are smaller than they than
they appear. But that's not really that doesn't matter. It's
whether they're like in your back seat or not. Yeah,
and they actually um, there are have been rumors over
the years at department stores put convex mirrors, slightly convex
mirrors in their changing rooms to make you like a
pear tallerant thinner in the clothing that you try on.
Remember that Seinfeld where Eline like buys that dress, figured

(17:48):
that they had a skinny mirror, And I think Barneys
are blooming deals. Yeah, forgot about that. Yeah, I don't know.
I think that's probably urban legend, but who knows, um chuck.
The other one, like we said, was concave convert jing.
We use those for holograms. They also use that to
light the Olympic torch. Yeah, I didn't realize that either.
I think that's a nod to Archimedes too. Probably, so

(18:09):
you're probably a little more um acquainted with convex mirrors.
No concave mirrors for like shaving or No, those horrible
mirrors that show your like hair and detail. Those are awful,
they really are. Don't ever look in those nonreversing mirror,
which really is pretty simple. It's just two mirrors perpendicular

(18:31):
to each other, right, Yeah, And the deal is with
that they meet at the angle and so you technically
can see a non reverse image, but you've got that
line running down the center of you. They don't make
like a flat, single nonreversing mirror. No they don't. I
think it's physically impossible. It's not like they don't make
it like they're not interested. It's just can't be done.

(18:51):
But what's funny is there's a guy named um John
Derby who has a patent. In seven when he was alive,
he had a patent for a nonreversing mirror. By sticking
two mirrors together, I could get a patent for that.
I could fill out the patent application for that you could. Yeah,
it's like take mirror A and stick it perpendicular to

(19:11):
mirror B. Right there, give me my patent. Well, but
then John Derby's family would come after you. Hopefully it
ran out by now. And just for simpleness, Josh, two
way mirrors as seen in every cop shakedown movie ever made. Yes, now,
this is fascinating, Chuck. How does the two way mirror work? Well,
it's really pretty easy. It's just it's the same concept
of the mirror, but it's a very thin. It's very

(19:34):
much a lighter reflection the material they use and the
coated side. When it faces the lit room, some of
the light reflects and some goes into the dark room
behind it. So basically like you know, you can't you
can see only see one way right because of the
light mainly. So it's just like very thin reflective surface

(19:55):
where if you're not if you turn in, if you
turn on lights in both rooms, you'd be we'll see
through that reflective surface, right, Yeah, it's all about the lighting. Yeah,
and that's a movie there. There's several movie mirror things
that are done in like every movie, and that's one
of them. With the cop movie and inevitably the person
getting questioned will always walk right up and like be
staring into the face of the person on the other

(20:16):
side that they can't see. And then the other favorite
of mine, which one of the SNL shorts aped, was
um the classic horror movie scene where you where you
look in the medicine cabinet and the mirror and then
you open the medicine cabinet and then you close it
and the dude is right behind you. That's a classic.
It is there's um again on YouTube. I think there's

(20:36):
a a montage, like a four minute montage of that
being used over and times. Dude and it still gets people. Yeah,
but now that the whole spin is to do that
and then there's not someone there, and then they'll turn
around and that's where they are something. Yeah, just jerking
the audience around. That's in there too. Uh oh it
is huh yeah. Yeah, it's not just people closing there

(20:56):
someone saying there's ones where they're not standing there. Yeah.
I love those movie conventions that are The other one too,
is it doesn't even do with mirrors, but the scene
where you're where someone is searching for the files and
then the person's office after dark, and you know they're
coming up the steps and they opened the door and
you're like they're pinched. And then they opened the door
and the person is gone, and there's like a window open, right,

(21:18):
and it's just like the curtains. Hundreds and hundreds of
time is still done yet I'm still like, oh my gosh,
here they come. What about Poultergeist, the great classic mirror
scene where the guys like picking at that little blister
and ends up pulling his whole face off. Yeah, that's
pretty creepy. Yeah, classic, Thank you Toby Hooper? Did he
make that? Yeah? I like got this right? He produced it, right,

(21:40):
that's right. I always think he directed that. What else, Chuck, Well,

(22:07):
there's some superstitions around mirrors in folklore, um summoning Bloody
Mary by saying her names three times in a mirror,
or candy Man, if you're a little more recent, that's
a good one. Breaking a mirror supposedly bad luck because
um for seven years, because they believe that the soul
regenerates every seven years. Yeah, that explains it, doesn't it. Yeah,

(22:29):
And that's why vampires have no soul. That's why they
can't see themselves in mirrors, and a couple of them
I haven't heard of are if you give birth and
look in a mirror too soon afterward, you will see
ghostly faces peek out from behind the reflection. I've never
heard that one in you know, I had heard of
sitting shiver though. Yeah, what's the deal with that one? Well,
if you're Jewish and somebody dies, part of the morning

(22:51):
process is to cover all the mirrors in the house.
Uh to say that in the Talmud? Shut up, chuck. Also,
we have gotten conflicting um information about whether or not
it is taboo among Judaism to be cremated, did you notice? Yeah?
And what we and I'll stand behind what we found,

(23:13):
which was that reform Jews will do it, but they
it's still not like encouraged. And then but it is
actually forbidden in the actual Jewish text. So there, fine,
is that it? I think that's about it? Um? Oh,
New Year's Eve, right, Yeah, I hadn't heard of this
one either. If you go up to a mirror on

(23:33):
New Year's Eve with a candle in your hand, and
you say the name of a dead person, probably a
dead loved one, um, in a loud voice, their face
should appear in the mirror. Never heard that. And this
is my favorite one, the ancient Chinese mythology. Um, you
know how you see weird movement in like the corner
of a mirror every once in a while. Have you

(23:54):
ever noticed that? Uh? Sure, I just figured it was
like your mind playing tricks on you. I'm sure it
is on the through Chinese pal Then what it is are, um,
the mirror people the mere Kingdom. There's a group of
opposites who live in the mirror Kingdom, and they are
sworn to do battle with us. Yeah, and if this
were North mythology, we'd lose, and we may lose in

(24:17):
this case too. But they are in a I guess
a magical slumber. Um. But when we catch a little weird,
unexplained movement in the corners of mirrors, Um, this is
these people stirring in their sleep, waiting to wake up
and kill us all in our sleep. I'll remember that
next time I see something in the corner of my eye.

(24:37):
So that's it for mirrors. Um, that's it, I mean,
that is it? Nothing else? There is literally nothing else
to say about mirrors. Nope. And uh, if you think
that there is we defy you to go to how
stuff works dot com and type mirrors into the search bar.
Pale listener, mail time listener, Maile John, this is a little,

(25:01):
uh cool organization that we want to support here And
how long you've been smoked free, buddy? It's over four
months now? Crazy so proud, Hi Chucking Josh. I travel
outside the city every weekend listen to your podcast, and
I always share my new knowledge with friends. Needless to say,
I'm the Friday Night's smarty pants and I rather like it.

(25:21):
Why I'm writing, I want to promote the New York
City Walk to Beat Lung Cancer. I'm one of the
head chair persons. At twenty years old. I never thought
I would share anything, but I love my new responsibility
as I am making a huge difference to an underdog
cause how could cancer be an underdog? Josh? Is the question?
I don't know. I think it's pretty bad. When you

(25:42):
hear someone has lung cancer, the first thing that comes
to your mind is, probably did hear she smoked? It
never fails. It is a valid question. Uh. Funding for
lung cancers completely dwarfed by other cancers that are nearly
as fatal and is completely due to the stigma of
a smoker's disease. I get turned away by sponsors and
media all the time him because no one wants to
support a disease that is so preventable. But the thing is,

(26:04):
it isn't people who get LC second hand for no
reason at all happens all the time. Why don't people
ask those with skin cancer if they wore sunscreen, or
people who have heart attacks if they ate. Well, it's
just silly. But looking at the numbers, it just doesn't
add up. Um. So here's what we're gonna do, Jess,
since you were the chair, there's an event in New

(26:25):
York City, New York City. It's called the Walk to
Prevent I'm sorry, the Walk to Beat Lung Cancer Lung Cancer,
and it is October two thousand ten in Battery Park.
And if you would like to take part in this
Walk to Beat Lung Cancer, Jess would really appreciate it.
You can go to a website www. Dot longevity see

(26:47):
what they did there, dot org slash NYC walk, so
that is l U n G E v I T
Y dot org slash NYC Walk, or Twitter. You can
follow this and get information at Walk number four lung
cancer all one word or Facebook at Walk to Beat
Lung Cancer and Jess would appreciate your participations. Are New

(27:10):
York City buddies that we met while we were there,
spread the word and get out and walk. Yeah that's awesome.
And if you're one of those people who poo poo's
lung cancer or helping battle lung cancer, yeah, maybe it's
time you took a long look in the mirror because
you could be a jerk. If you have any kind
of organization like chucking out and give a shout out

(27:32):
to we consider those on a case by case basis.
Don't we chuck We sure you? Um, it definitely doesn't
help or it definitely doesn't hurt to uh grease the wheels,
if you know what I mean. And we're not talking
about cash prizes now, we can't legally do that, can't
we know? Uh. You can tell us about your organization

(27:52):
in an email to send it to stuff podcast at
how stuff works dot com. For more on this and
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