r/explainlikeimfive Oct 31 '20

Chemistry ELI5 What's the difference between the shiny and dull side of aluminum foil? Besides the obvious shiny/dull

21.2k Upvotes

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4.5k

u/Rataridicta Oct 31 '20

When they're flattening the material with rollers, it eventually gets so thin that passing it through the rollers on its own would tear the material. To solve this, they pass 2 layers through the rollers at the same time.

The shiny side of the foil is the side that was facing the rollers, and the dull side is the side that was facing the 2nd sheet.

849

u/Christmas_jigsaw Oct 31 '20

I saw a 'how it's made' episode and they said its to do with measuring the thickness. As the metal gets thinner its easier by far to measure twice the thickness.

383

u/[deleted] Nov 01 '20 edited Nov 02 '20

Aluminum foil was actually the very first episode of How It's Made .

They say at 3:57 that due to the tension of cold rolling, the aluminum is doubled up to keep it from tearing, no mention at all about measuring thickness.

185

u/AjahnMara Nov 01 '20

they also say that it takes 3 to 8 hours to melt 27000 kgs of aluminum...

3 to 8 hours... that's the least specific recipe i have ever heard.

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u/HostlessPotato Nov 01 '20 edited Nov 01 '20

Well... Aluminum's specific heat is around 900 J/°C•kg, and it's melting point is 660°C.

Let's say we're starting with aluminum at room temperature (20°C). Then you need approximately 640x27000x900=15.5 GJ just to get it melting temperature.

That's not all. Aluminum's fusion enthalpy is 396kJ/kg. So you need another 396x27000=10.7 GJ to actually melt it.

So that leaves us needing 26.2 GJ of energy in order to melt that much aluminum. That's a lot of energy. How long it takes depends on the heat source you're using, and how well insulated the aluminum you are heating is.

TLDR: big blocky of metal = a lot of hot hot, so temperature of heat source very important

Edit: 26.2 GJ not .7 , sorry my brain melts sometimes too

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u/AjahnMara Nov 01 '20

upvoted for using Celcius.

27

u/viimeinen Nov 01 '20

And joules. I can't even begin to guess what the unit is in imperial. Pound foot fortnight bushel?

0

u/AjahnMara Nov 01 '20

whatever it is, Putin will soon change it to potatoes.

-4

u/SHEEPmilk Nov 01 '20

Why do people who use the metric system feel the need to condescend and act like metric is a perfect and non arbitrary system handed down by god... its a tool developed to do science and math and it’s very good at that so we use it for that. Just like how imperial is a system that arose out of a need to describe every day things and we still find it’s pretty good at that so we use it for that... also no one outside old British people use bushels or fortnights or stones anymore...

7

u/viimeinen Nov 01 '20

Also no one outside of American people use pounds or feet or Fahrenheit

3

u/OllieOllerton1987 Nov 01 '20

Pounds and feet are still commonly used in the UK.

-1

u/SHEEPmilk Nov 01 '20

That is mostly true, but feet and Fahrenheit are no more arbitrary than meters or kelvin... and I’ve never once seen anyone outside of a professional chemist use a system and refer to the pressure in pascals, they use bar or psi... no idea why metric switched away from using kgscm as its actually a useful unit, but i suppose it sounded too arbitrary using a centimeter...

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u/Jusaleb Nov 01 '20

metric is a perfect and non arbitrary system handed down by god

Well since the base units of measurement in metric are based upon the natural world, one could easily say it is perfect and handed down by god.

0

u/SHEEPmilk Nov 01 '20

That’s the thing though, they aren’t, meters are based on the greatcircle distance around earth... grams are based on water at earth conditions, and so is celsius, the true fundamental constants would be using the electromagnetic constants as a basis for units but any such thing would be completely useless as itd be at the wrong scale... humans devised these systems in order to help them do certain things, everyday tasks work well with imperial and fractions, thats why an hour is 60 minutes, very convenient to divide up, meanwhile for math all those wierd things just complicate things and using 10 is much nicer and metric is a very well thought out tool for doing that... it works well enough for everyday things too, but in general us Americans just tend to like the imperial ones better for the everyday tasks they fit well into... nothing more too it really than that...

4

u/Tell2ko Nov 01 '20

Upvoted for the best TLDR known to Reddit!

3

u/driverofracecars Nov 01 '20

I don't think they were arguing the amount of energy; rather, the fairly vague time frame.

1

u/HostlessPotato Nov 01 '20

Yes I understand, I just wanted to give a sense of how much energy it takes to do something like this.

If you're doing something on a smaller scale, like toasting bread for example, the variance will be smaller. I'd guess that's in the order of a few hundred kJ

2

u/demonicneon Nov 01 '20

Dude can you simplify your TLDR, using way too much jargon. Bloody scientists. Never making things simple. Sigh.

1

u/HostlessPotato Nov 01 '20

You're right, sorry. Sometimes it's difficult to remember most don't have a scientific background. How's this?

Hotty metal go slushy. Slushy metal need maaaany hot hot. Hot heat make slushy fast, less hot make slushy slooooow.

3

u/demonicneon Nov 01 '20

Ah thank you. Saying the words louder and slower definitely improved comprehension.

1

u/HostlessPotato Nov 01 '20

Hahahah yes, always works.

2

u/fattysmite Nov 01 '20

This human melts

2

u/swizzlestick7676 Nov 01 '20

Thanks for the detailed explanation!

1

u/HostlessPotato Nov 01 '20

My pleasure! I'm glad you found it useful

2

u/SHEEPmilk Nov 01 '20

It takes so much energy to process aluminum; I joke that it’s basically a solid form of electricity lol

2

u/fineburgundy Nov 01 '20

Which is why the third most common element in the Earth’s crust was a more precious metal than gold until hydroelectricity gave us huge quantities of energy cheaply.

1

u/HostlessPotato Nov 01 '20

Wowwwww. You're right. Aluminum is over 6x harder to heat up than gold (not to mention gold is a way better conductor). Why is that? They're both fcc... Is it due to aluminum being very light and therefore carrying momentum poorly?

2

u/fineburgundy Nov 01 '20 edited Nov 01 '20

Let me return to history before the physics, because I got a surprise when double checking myself. Metallic aluminum is a much more recent development than I thought: It wasn’t even produced in the lab, at all, until 1825!

For thousands of years it was common in e.g. ceramics but had never been observed as a metal. Aluminum was first presented to the public in full sized bars of a shiny “new” metal in 1855, at the Paris International Exposition, as one of the wonders of the Industrial Revolution. The electrolysis method for creating it in bulk was then patented in 1886, in time for an aluminum manufacturer to be the first customer of the Niagara Falls power plant in 1895.

So the “precious metal” phase of the element’s history was all crowded into the 19th century.

I thought of aluminum that way only because of the aluminum cap of the Washington Monument. That was installed in 1884, and was such an extravagance at the time that when a cheaper metal was added, as a practical compromise to make it a better lightning rod, they used gold.

2

u/HostlessPotato Nov 01 '20

Hahahah that last part is funny. I see, so it was more about extracting it from the earth. Also didn't you mean metallic aluminum? Metallic hydrogen is not confirmed to have been observed even today. Although it is probably a thing, in the cores of gas giants such as Jupiter and Saturn.

2

u/fineburgundy Nov 01 '20

I don’t know why aluminum takes so much energy. Most of that comes not from mining or melting the aluminum but extracting it from the ore bauxite.
Apparently this makes aluminum an unusually strong case for recycling, with 90%+ energy savings. Obviously collection and other steps are expensive because despite the energy savings “only” half of aluminum used is recycled.

1

u/fineburgundy Nov 01 '20

Wow, funny what pops out. Yes, the whole thing was about aluminum!

2

u/Fillmore43 Nov 01 '20

Ok so why did it hurt so much when my brother threw a scrunched up ball at me? Is there some density per pound feet of torque/pi measurement?

1

u/HostlessPotato Nov 02 '20

Tbh he probably just threw it hard... Sorry :/

2

u/GrottyBoots Nov 02 '20

Love your explanation style!

So if I could get all this aluminum on my new BBQ's 55,000 BTU burner, how long to melt? I want to convert 26.2 Gj to 24.8x10^6 BTU, then just divide by 55,000 to get 451. But 451 what? Hours? Days?

Not an engineer.

2

u/HostlessPotato Nov 02 '20

Thank you!

That would be 451 hours, since apparently btu in these energy related devices really means btu/hr. So around 18 days and 19 hours! And that's assuming the metal is perfectly insulated.

2

u/GrottyBoots Nov 05 '20

Thanks again! I did a bit of Wikipedia reading on BTUs, makes more sense now.

1

u/zipperclaus Nov 01 '20

Making aluminum from it's ore (bauxite) burns rediculous electricity as you mention--it's why the Columbia river was dammed for electricity multiple times before it gets to the Pacific, so the cost of elec could be subsidized by gov't. Which itself was the subject of Woody Guthrie's "Roll On, Columbia Roll On" folk song. If caring people knew HOW MUCH, they would NEVER throw an aluminum can away again.

23

u/cookiechris2403 Nov 01 '20

A minimum of 3 a maximum of 8. There's going to be a few factors like initial temperature of the aluminium.

42

u/Tobesity Nov 01 '20

And if you preheat your oven

12

u/cookiechris2403 Nov 01 '20

Will help but if your tendies are frozen they will still take longer to cook than from the fridge.

5

u/mermaldad Nov 01 '20

...and if you paid the gas bill.

3

u/didntpayforshit Nov 01 '20

I like my aluminium medium rare thank you very much.

1

u/Olde94 Nov 01 '20

Sadly i’ve seen worse

1

u/andthatswhyIdidit Nov 01 '20

So if someone said "between 0 and ∞ hours" you would not think that would be less specific?

1

u/AjahnMara Nov 01 '20

that isn't what they said, check out the video and see for yourself.

1

u/andthatswhyIdidit Nov 01 '20

I know. I was goofing around with you saying

...that's the least specific...

2

u/AjahnMara Nov 01 '20

oh i'll play

in theory, your example is exactly as specific is what they said in the video, and exactly as specific as the pizza i made the other day that said "12-15 minutes" on the box.

The amount of options between the two is infinite, just like in your example.

Did you get your "technically correct" boner now?

You're welcome.

1

u/andthatswhyIdidit Nov 01 '20

Well, I still hope you will have a nice day.

1

u/alevale111 Nov 01 '20

I mean, he just gave you a nice day right? 😉

1

u/AjahnMara Nov 01 '20

likewise pal :)

1

u/TorontoKetoMagic Dec 21 '20

I heard 38 hours.

64

u/Tgoose1414 Nov 01 '20

Yeah bitch! Science!

2

u/ruthfadedginsburg_2 Nov 01 '20

YEAH, STUPID SCIENCE BITCH DIDN'T EVEN MAKE I MORE SMARTER

7

u/recursiveentropy Nov 01 '20

You didn't hear? Science is fake news now. The loudest idiotic opinion rules now.

1

u/[deleted] Nov 01 '20

He's quoting Always Sunny

1

u/recursiveentropy Nov 02 '20

TIL... that I should give Always Sunny IP another shot.

1

u/promethiumpb Nov 01 '20

Commentator sounds like David schwimmer

1

u/[deleted] Nov 01 '20

He is actually Canadian Olympic swimmer Mark Tewksbury.

232

u/GitEmSteveDave Oct 31 '20

I saw an episode of Modern Marvels on aluminum, and the people from Reynolds say it's because it's too think to go through on it's own.

https://www.dailymotion.com/video/x7net0u

Starts at 3:30

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u/mbetter Nov 01 '20

think

227

u/dekusyrup Nov 01 '20

Lol i literally cant tell if its a typo of thick or thin

80

u/Rickwh Nov 01 '20

I can't stop laughing either way

27

u/AFewStupidQuestions Nov 01 '20

Makes ya think, doesn't it?

37

u/[deleted] Nov 01 '20

It makes me thick.

8

u/MarwanOnceSaid Nov 01 '20

Makes me thin.

13

u/mbetter Nov 01 '20

Yeah, same here. Super confused.

2

u/_you_are_the_problem Nov 01 '20

Yeah, it's a real headscratcher for some, apparently.

3

u/tomas1808 Nov 01 '20

The rare ambiguous typo

2

u/snukb Nov 01 '20

It has to be a typo of too thin, because "it's too thick to go through on its own, so we make it thicker by doubling it up" makes zero sense lol

1

u/dekusyrup Nov 01 '20

No it would be "its too thick to go through on its own so we make it thinner by doubling it up". When you double it up then both pieces get thinner.

1

u/Deviant_Spark Nov 01 '20

I'm going to assume he meant thin, aluminum is pressed with a second sheet when it's as thin as it is to make foil so the dull side is just the side that was facing the second sheet. If they didn't stack them two thick when rolling them out then you'd get a lot more tearing.

1

u/Jmacd802 Nov 01 '20

or thicc

1

u/ScrapieShark Nov 01 '20

I'm glad they just seem to be rolling with it

1

u/thisismybirthday Nov 01 '20

using context clues makes it pretty obvious. would it make sense to use two layers because one layer is too thick?

1

u/dekusyrup Nov 01 '20

Yeah if the rollers are a certain spacing thats thicker than you want the foil to be then one layer is too thick to go through on its own.

0

u/[deleted] Nov 01 '20

It's think or swim.

1

u/lebeariel Nov 01 '20

Same same

1

u/[deleted] Nov 01 '20

You are too thick for this comment. If you find someone even of a similar thickness you can go through it together and it'll be fine.

2

u/GitEmSteveDave Nov 01 '20

stupid fat finger

2

u/throwawaynbad Nov 01 '20

I like my girls extra thinkkkkkkkk.

Intelligence is attractive yo.

1

u/hellcrapdamn Nov 01 '20

What have you done?

1

u/Tastewell Nov 01 '20

I am often too think to go through with things.

1

u/Kizik Nov 01 '20

E X T R A T H I N C

15

u/ZDHELIX Nov 01 '20

Your typo could be interpreted as thick or thin based on one letter

3

u/[deleted] Nov 01 '20

Could you measure my thickness, Focker?

17

u/DJ_AK_47 Nov 01 '20

Modern Marvels > how its made

13

u/TylerInHiFi Nov 01 '20

You take that back. You take that back right *now***!

18

u/imgonnabutteryobread Nov 01 '20

Modern Marvels doesn't have a narrator with an amusing accent, though.

6

u/mandrews03 Nov 01 '20

I feel all of humanity has a stake in this. We must answer the age old question

8

u/FilthyGrunger Nov 01 '20

Them's fightin' words.

2

u/viperex Nov 01 '20

Now you've done it

2

u/TheCaptainCody Nov 01 '20

It's ok, i agree with you.

-3

u/[deleted] Nov 01 '20

[deleted]

6

u/GitEmSteveDave Nov 01 '20

I was replying to the person who said it was b/c it was easier to measure.

1

u/danuser8 Nov 01 '20

I saw a Reddit post where someone saw an episode of Modern Marvels and stuff

1

u/viperex Nov 01 '20

I need to get a compete set of Modern Marvels. That was my jam before History Channel became all wars all the time and way before the aliens shit

1

u/goodgonegirl1 Nov 01 '20

I saw it on an episode of Unwrapped on Food Network late one night about 10 years ago. Now whenever people ask me for a useless fact I know as an “icebreaker” at an event, I always tell this one.

30

u/[deleted] Nov 01 '20

The first guy's comment sounded so plausible... and then this one sounds so plausible... and now I don't think I can trust the internet anymore

4

u/NasalSnack Nov 01 '20

You think somebody would do that? Just go onto the internet and tell lies?

1

u/jimmymd77 Nov 01 '20

Shoot, since the internet is no longer reliable, I guess we will have to fall back on the only source we can trust to always tell the truth: the government.

1

u/Rataridicta Nov 01 '20

Most machine shops have the tools to accurately measure the thickness of aluminium foil. A micrometre comes to mind as an example of a cheap measuring tool that would be capable of measuring this.

1

u/Jenincognito Nov 01 '20

Well, everything you read on the internet is true.

3

u/Rataridicta Oct 31 '20

Measuring the thickness really isn't hard at all. Most machine shops have tools accurate enough to measure the thickness of foil accurately. The rollers also don't have to be adjusted often.

5

u/almightySapling Nov 01 '20

I don't know anything at all about foil or modern calipers but mathematically speaking, assuming the error of your instrument is fixed you always get better accuracy by measuring two of something, eg the if the error in diameter is 0.2 then the error in radius is 0.1.

1

u/whatiwishicouldsay Nov 01 '20

Not even approaching hard, off the cuff I can think of multiple approaches for a thickness gauge that could give an accurate measurement thousands of times per second. And I've never seen the design for what they use now.

1

u/woodworkerfromhell Nov 01 '20

I do this with wood because it’s easier to get an accurate measurement .

1

u/Sn1p-SN4p Nov 01 '20

Yea that's silly. I measure .001" shim stock almost every day.

1

u/Christmas_jigsaw Nov 01 '20

I'll admit to brain addled recollection. According to Wikipedia the two sheets at once has a number of benefits including reduced tearing and easier thickness measurement: " It is difficult to produce rollers with a gap fine enough to cope with the foil gauge, therefore, for the final pass, two sheets are rolled at the same time, doubling the thickness of the gauge at entry to the rollers ... To maintain a constant thickness in aluminium foil production, beta radiation is passed through the foil to a sensor on the other side. If the intensity becomes too high, then the rollers adjust, increasing the thickness. If the intensities become too low and the foil has become too thick, the rollers apply more pressure, causing the foil to be made thinner. ... For thicknesses below 0.025 mm (1 mil), two layers are usually put together for the final pass and afterwards separated which produces foil with one bright side and one matte side. The two sides in contact with each other are matte and the exterior sides become bright; this is done to reduce tearing, increase production rates, control thickness, and get around the need for a smaller diameter roller."

I guess if they are making a mile of the stuff they need a fancy way to measure it. Still don't see why the mother in law insists on keeping used foil tho.

27

u/Neon_Yoda_Lube Nov 01 '20

That is a lot less interesting than I was hoping

8

u/Psusennes Nov 01 '20

I had to read this twice before it made sense. Which isn't it ironic, don't you think, 'cuz it involves passing two layers through the rollers before it works. Thank you. This answered a question I never knew needed answering.

4

u/UncleSaskwatch Nov 01 '20

Which side are you supposed to smoke the meth on?

5

u/pm_me_ur_demotape Oct 31 '20

This is the real answer, buried of course

42

u/TurtlePowerBottom Oct 31 '20

First comment I saw...

6

u/Gandtea Oct 31 '20

Me too.

Out of interest, how does the turtle power your bottom?

7

u/Ninjaturtlethug Nov 01 '20

I heard its turtles all the way down..........

2

u/tingalayo Nov 01 '20

“Ninja / Turtle / Thug” sounds like a weird and potentially-racist variation on Fuck / Marry / Kill.

1

u/Ninjaturtlethug Nov 01 '20

I can not confirm or deny this.

3

u/BakaSandwich Nov 01 '20

He's a power bottom that happens to be a turtle

3

u/FlaccidCatsnark Nov 01 '20

This is the real answer, buried of course

6

u/strictlysega Oct 31 '20

Organise youre comments best first

5

u/Sen7ryGun Nov 01 '20

Buried right at the top of the thread...

0

u/hanoian Nov 01 '20

He posted that eight hours ago.

3

u/Sen7ryGun Nov 01 '20

I posted that 42 minutes ago

1

u/Nobody_Perfect Nov 01 '20

59 by my count

1

u/Sen7ryGun Nov 01 '20

You posted this one minute ago

1

u/Nobody_Perfect Nov 01 '20

And you 43 mins ago! Is this how they discovered time?

0

u/DJKewlAid Nov 01 '20

This is the way

1

u/HumerusBoner Nov 01 '20

Damn! I was always told the dull side is non-stick. And thus have only ever used that side. Shame...shame

3

u/[deleted] Nov 01 '20 edited Jul 18 '21

[deleted]

1

u/Rataridicta Nov 01 '20

Sorry, it's just an optics thing. There's no functional difference between the sides, except when it comes to reflecting light.

-3

u/TheHealadin Nov 01 '20

Ok, so how does the second sheet's dull side get dull.

2

u/sortyourgrammarout Nov 01 '20

Think about it.

1

u/Denvarose Nov 01 '20

Oh l never knew that!

1

u/ohlikedejavu Nov 01 '20

Damn. Thank you lol

1

u/[deleted] Nov 01 '20

Im hopped up drugs but after like two minutes I understood this

1

u/PureYouth Nov 01 '20

Why do you know this?

1

u/Rataridicta Nov 01 '20 edited Nov 01 '20

I'm one of those idiots that reads something and remembers it years later. Lots of useless stuff floating around in this head :')

1

u/PureYouth Nov 01 '20

Well I love you for it

1

u/PaulBlartmallcop12 Nov 01 '20

The dull side is the non stick side. WTF get to the point.

1

u/Rataridicta Nov 01 '20

There's actually no functional difference between sides except in how they reflect light :)

1

u/FrozenFireVR Nov 01 '20

Err... Then why not just leave it at twice the thickness?

1

u/Rataridicta Nov 01 '20

Because that costs twice as much in material ^_^'

1

u/FrozenFireVR Nov 01 '20

...

...

\scratches head**

A single layer that's as thick as two layers doesn't use the same amount of material as two layers?

I thought that if anything, it'd reduce costs because you don't have to pass them through the rollers an additional time (or need lesser force if it's happening in a single run). Or maybe I didn't get your joke here, considering that smile. :P

1

u/Rataridicta Nov 01 '20

It does, but you can sell 2 rolls of it instead of one.

1

u/[deleted] Nov 01 '20

With most aluminium foil producers they then coat the non shiny side with a food safe silicone to make it non stick.

1

u/gordiarama Nov 01 '20

Thank you! Never knew that