The authoritative public forum
  for Metal Finishing since 1989
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Does a penny rust?

Q. Hi, my question is "does a penny rust?" I am asking this question because I need to know the answer for homework and I was wondering if any one at this site knew the answer.

Chad H [last name deleted for privacy by Editor]
- Akron, Ohio

A. Hi Chad,

A penny doesn't rust.

Why no rust? Because RUST refers always and solely to iron (yes, even stainless can rust, I've often seen it!)

Even steel (a refined species of iron) contains ferrous materials. The natural state of steel/iron would be Fe₂0₃ or Fe₃0₄, ie. iron oxide or rust. There is another state of rust ... the saying that Old Soldiers Never Die they Just Rust Away!

I hope that this highly useful information will give you an honorable pass at your homework!

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

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The term "rust" usually refers to the process of oxidation of iron-based materials. Pennies do oxidize, but this oxidation is called "patina" or "verdigris". Newer pennies are made of zinc with a thin film of electroplated copper over the top. Zinc can also corrode, as well, but it's not called "rust". So the logical answer would be "No, pennies do not rust..."

George Brackett III
- Utica, New York

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Hello Chad,

Contrary to popular opinion, there are some pennies that could rust! I have a collection of pennies, and during WWII, the government rationed copper and produced iron pennies. I do believe iron is a ferrous material and when exposed to ^^the elements it forms iron oxide, also known as rust.

Jake Koch
G. J. Nikolas &Co.,Inc.

Bellwood, Illinois

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You're absolutely correct- I think the teacher asked a "trick question". Due to a copper shortage during WWII, 1943 pennies (most of them, although a rare handful of a copper alloy are known to exist and are quite valuable) were minted from steel with a zinc coat. Since the zinc quickly wore off, many of these steel pennies have already rusted into oblivion...the correct answer is, "Yes, most pennies minted in 1943 can rust..."

George Brackett III
- Utica, New York
 

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Pennies aside, iron IS ferrous. It's an element. If it's got iron in it, then it's ferrous. Steel is a more useful alloy of iron and carbon, plus lots of other stuff.

Yours pedantically,

Ian Brooke
university - Glasgow, Scotland

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Hello Ian,

Thanks for the clarification. Sorry, my fingers sometimes work faster than my brain, that should read "the" elements, i.e. sunshine and rain.

Jake Koch
G. J. Nikolas &Co.,Inc.

Bellwood, Illinois

Yes a penny can very well rust. Rust as you might want to know, is caused by pollution in the air. However, acid rain helps speed up the process. I don't know anything else and I would like some help of my own. I need to know more than what causes a penny to rust besides rain and oxygen. So if you can help me I would greatly appreciate it!

Gabriel S [last name deleted for privacy by Editor]
- California

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Gabriel, you don't say what grade you are in, but as previously explained, today's pennies cannot rust because rust is iron oxide and pennies do not have iron in them (except for 1943 pennies).

Although you are not quite right about rust being "caused by pollution in the air", there is a degree of truth to the statement because some kinds of pollution can accelerate rust and other corrosion. So some things that can cause pennies to corrode would include rain, oxygen, acid, other forms of water besides rain, salts, and pollution.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Hi I am doing a project on Iron and couldn't help but saying that iron penny's seem to be an interesting subject. I think it is cool that they actually made iron pennies. My teacher has never heard of them before I know for a fact that iron does rust I have seen it on cars like that other dude so to answer your question yes iron does rust and there are old iron pennies.

Dillon B [last name deleted for privacy by Editor]
- Newport Ctr., Vermont
2006

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Is a 1943 zinc penny worth anything? Robin Mcgee hobbyist - Jackson, Michigan 2006 Probably between a dime and a dollar, Robin. See the eBay listings immediately below. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey 2006

In reference to everyone's inquiries to whether pennies are able to 'rust' or not; all pennies ,regardless of being forged of copper or iron (1943 zinc ),have the same properties that enable them to oxidize. All ferrous and even nonferrous metals,have this same quality. The only difference is the time of decay.

Cory P Murphy
- Houston, Texas
2006

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Not really, Cory!

You can make flour from rice or corn, you don't need wheat. But you can't make wheat flour from rice or corn.

And you can get other metals to corrode, you don't need iron. But you can't make rust from other metals because the word 'rust' means corrosion products of iron, just as wheat flour means flour from wheat.

Gold and some other precious metals don't corrode regardless of how much time you wait. That's why they are still found in metallic form in a world that is billions of years old.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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I think that a penny does rust because if you had an old car made out of iron...don't you think it would rust.its just the same but,it a penny that's rusting.also a penny is made out of copper iron so..what does that mean...o yeah it can rust!i know this cause I'm doin an project on it and I'm just 12 and the 6th grade.

IF YA HAVE ANY ? BOUT MY COMMENT ......RESPOND BACK

Edriana J [last name deleted for privacy by Editor]
- Palm Bay, Florida
2006

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2006

Your response was incorrect, Edriana. Only things that are made from ferrous metals (iron, steel) can rust because rust is defined as the corrosion product of iron. Pennies are not made of steel (with the exception of 1943 pennies) so they cannot rust.

Fish can rot and cabbage can rot, but a cabbage can never become a rotting fish. Pennies can corrode but they can never become rusty. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

OK WELL THANKS FOR THE HANDS UP TED MOONEY, BUT I STILL THINK THAT AN PENNY CAN RUST...EVEN THOUGH you SAY NO....I'M STILL GONNA TEST IT AND SEE... TRYING THINGS WANT HURT RIGHT?.....RIGHT. ALSO I HAVE AN ? FOR you TED MOONEY SINCE you RESPONDED BACK....IF AN PENNY DOESN'T RUST?THAN HOW COME WHEN WE HAVE PENNIES THAT are BRAND NEW...WHY DO THEY TURN INTO DARK DARK DARK BROWN? ALSO,I'M DOING A PROJECT ON WHICH TYPE OF LIQUID WOULD RUST A PENNY THE FASTEST?AND I'm USING WATER, VINEGAR, AND BLEACH ⇦ bleach/sodium hypochlorite in bulk on eBay or Amazon [affil links] AS MY LIQUIDS?WHICH ONE DO you THINK WOULD RUST IT THE FASTEST? ALSO,TED MOONEY CAN you GIVE ME SOME WEB SITES ON RUSTING PENNIES PLEASE CAUSE I CANT FIND ANY MORE INFO. PLEASE AND THANKS YOU VERY MUCH FOR YOUR HELP BYE!

Edriana J [returning]
- Palm Bay, Florida
2006

You are right that it can't hurt to test it, but there are many things that are brown that are not rust, including coffee, chocolate, tobacco, wood furniture, and the tarnish on pennies. As a tree leaf dies it curls up and turns brown -- but the leaf is not rusting. As a penny tarnishes it turns brown but it is not rust because, as I said before, the word "rust" has a particular meaning: the corrosion product of iron or steel. The brown stuff on old pennies is "tarnish", not rust.

If you travel up north in the winter you may see white powder falling from the sky and it may look to you like confectioner's sugar, and you may want to call it sugar -- but that doesn't make it sugar.

There are hundreds of letters about pennies and science projects on this site; use the search engine and look for "cleaning pennies". Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

I'M DOING AN EXPERIMENT ON WHAT TYPE OF LIQUID WOULD RUST A PENNY THE FASTEST? AND I'm USING WATER,VINEGAR,AND BLEACH AS MY LIQUIDS.SO IF you KNOW ANY THING ON DAT please LET ME NO CAUSE I NEED DIS FOR MY SCIENCE RESEARCH please AND THANKZ/ALSO EXCUSE ME FO MY WRITIN ITS KIND OF GHETTOISH...LOL

Edriana J [returning]
- Palm Bay, Florida
2006

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Please be very proud of your heritage, Edriana; our parents, grandparents, and ancestors worked hard in hopes of things being good for you and I. But be careful not to be proud of misspelling, whether deliberate or accidental, because it will probably interfere with you getting what you want and doing what you want as they hoped for you. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey 2006

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Hi Ted Mooney its me again sorry for writing you to much um....u were right about how a penny doesn't rust I went on www.answer.com and it said this :Nothing will make a penny rust because only things with iron in them can "rust", whereas a penny is made of copper plated onto zinc. But anything acidic or salty will cause the pennies to corrode.
that's what it said is it true?

Edriana J [returning]
- Palm Bay, Florida
2006

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Yes! You've got it, Edriana.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

YOU GUYS SAID PENNIES DID NOT RUST WOULD A NICKEL,OR A DIME,RUST?

SARA S. [last name deleted for privacy by Editor]
school - PITTSBURGH, Pennsylvania
2006

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There is no iron in nickels or dimes, Sara, they are both made of copper-nickel alloys today, although old dimes were made of silver.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2006

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Thank You so much Ted for helping me out with my science project based on rusting pennies.I got a HIGH A+ on my science grade thank you so much bye! Edriana J [returning] - Palm Bay, Florida 2007 Great work, Edriana! I'm proud of you, and appreciate that you acknowledged our very small effort. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey February 1, 2007

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HELP! COPPER OR SILVER? WHICH RUSTS FASTER?
I am doing a science fair on which metal takes longest to rust in tap water. I have zinc, copper, silver, aluminum, and a galvanized metal. I really need to know, which metal rusts fastest, copper or silver?

Lenny M [last name deleted for privacy by Editor]
student - Tulsa, Oklahoma
2007

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2007

We put your question onto a page that mostly already answers it, Lenny. But to repeat, a cod can rot and a cabbage can rot. But if you ask "which becomes a rotting fish faster if you leave it in the sun?", the answer is that a cabbage can never become a rotting fish. Similarly, rust is iron oxide, sort of "rotted" iron; copper and silver can never become rotted iron because they are not iron.

So your question might actually be which corrodes faster or which tarnishes faster. Now, which tarnishes faster is something your science fair project will determine. But neither will corrode a lot; after all, the copper piping in your house and your mom's silver service wouldn't be very useful if they quickly corroded away.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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um dear ted mooney..... I would like to thank you I read each of your responses and they helped me a lot! my science project was a 87 thank you so muchhhhh. maria m [last name deleted for privacy by Editor] hollywood, Florida December 9, 2008 December 10, 2008 Thanks so much for the kind words, Maria. You made my day. But YOU did the project, so be proud of your effort. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey

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Pennies do not rust. The stuff that gets on them is a form of corrosion. Corrosion is, when on copper, brown-ish mold begins to form. The word for this mold is Patina. I hope this helps you! Best of luck...

T. Hickson
- Chicago, Illinois
January 5, 2009

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February 13, 2009

The composition of pennies changed in late 1982, when zinc became the primary metal instead of copper. Before 1982, pennies were forged of 95 percent copper and 5 percent zinc. However, as copper became more expensive, it was abandoned as the primary metal. Pennies are now made of a zinc core and a thin copper coating. Coins made of zinc can cause a corrosive reaction when they are exposed to gastric acid. O'Hara and associates conducted a study to determine the radiographic appearance and features of corrosion in coins exposed to gastric acid.

The authors became interested in the effects of corrosion of a coin in the stomach when they encountered a two-year-old boy who presented to the emergency department with abdominal pain and vomiting four days after he had swallowed a coin. Initial radiographs of the child showed an intact metallic disk, which was presumed to be a coin, in the stomach. However, radiographs four days later showed a metallic object with a moth-eaten appearance. Endoscopy yielded a blackened, corroded 1989 penny and revealed a bleeding gastric ulcer.

The authors analyzed corrosion after exposure to hydrochloric acid in four types of coins: three silver-colored coins (a quarter, a nickel and a dime), six pre-1982 pennies that were worn but not intentionally damaged, six post-1982 pennies in good condition and six post-1982 pennies that had been scratched by scraping the edges until the zinc was exposed. Each group of coins was immersed in hydrochloric acid in a concentration that approximated gastric acid. The coins were rinsed and radiographed daily for seven days. Each group of coins was weighed at the beginning and at the end of the study. In addition, the penny retrieved from the two-year-old patient was weighed.

Immersion of the damaged post-1982 pennies in the hydrochloric acid was immediately followed by the development of bubbles of gas, indicating an immediate chemical reaction. With the undamaged post-1982 pennies, bubbles were seen on the surface by the third day of immersion in hydrochloric acid. Bubbles were not seen at any time on the silver-colored coins or the pre-1982 pennies. The surfaces of all of the coins grew increasingly dull as the duration of exposure to hydrochloric acid increased.

Radiolucent erosions were radiographically visible on the post-1982 pennies within 24 hours of immersion in the hydrochloric acid. After two days of exposure to the acid, full-thickness holes developed through the flat surface of these pennies. No radiolucent erosions or holes developed on the silver-colored coins or the pre-1982 pennies after seven days of exposure to hydrochloric acid.

All of the coins lost weight over the seven days of testing. The quarter, nickel and dime lost 12 percent of their initial weight. The post-1982 pennies lost between 5 and 8 percent of their weight. The penny retrieved from the child weighed 26 percent less than would be expected. The amount of weight lost in this penny far exceeded the amount of weight lost in the post-1982 pennies exposed in the hydrochloric acid experiment.

According to the authors, the chemical reaction between gastric acid and post-1982 pennies yields a highly absorbable form of zinc, zinc chloride. The zinc could have toxic effects. The two-year-old patient had absorbed a quantity of zinc that was equivalent to 22 cold-prevention lozenges. Reported toxic effects of excessive zinc absorption include local corrosion and ulceration of the esophagus and stomach, and gastrointestinal symptoms such as nausea and abdominal cramping.

The authors conclude that recognition of coin corrosion may become increasingly important as the number of zinc-based coins in circulation increases. They state that the radiographic appearance of a scalloped border and holes in an ingested coin should prompt endoscopic removal, because such features indicate that the coin has been retained for longer than one or two days. In such a situation, the potential for zinc-related morbidity is increased.

Nick,

Nick DiGi
- Newport Beach, California

My science fair project is testing after market rust inhibitor coatings on steel (I am going to use nails since they are cheap). For control I am using a steel nail that is not treated at all and one that has been galvanized. How can I speed up the rusting process for my coated nails to see which one works best?

Kendra F [last name deleted for privacy by Editor]
- Lakewood Colorado
October 5, 2009

Hi, Kendra. Interesting question because professionals also come to this site to ask how to accelerate corrosion and correlate it to real life. But the answer is that trying to accelerate corrosion changes its essential nature; the mechanism of accelerated corrosion is fundamentally different, so your accelerated test would only indicate that the rust preventative worked in an accelerated corrosion test, not in real life :-(

But you could try spritzing the nails with salt water several times a day, while leaving them out where they are exposed to the sun and the dew. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 6, 2009

I am in 5th grade and I'm doing a science fair project about rusting pennies.I used coke sprite and Sunkist to see which one can rust a penny fastest.And I made a big mistake! I waz reading all the things you know and found out that I was using 2009 pennies! What should I do!

Karen r [last name deleted for privacy by Editor]
student - Dallas,Texas
October 8, 2009

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Hi, Karen. People have spent their time explaining seven (7) times on this one page alone that pennies can't rust, so please use different words in describing your science experiment :-)

But I don't see a problem with 2009 pennies; the results should be fine.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 9, 2009

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hi, I'm in eighth grade and I am doing an experiment on oxidation on a penny and paper clip when submerged into different liquids. the liquids I used were coke,water,and oil. so far in my experiment both the penny and paper clip are turning black. just thought I could use some help on my research...

thanks

Andrea R [last name deleted for privacy by Editor]
- Jackson Heights, New York
January 4, 2010

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Hi, Andrea. You are asking, if I understand you, why does exactly the same thing happen (the items just turning black) regardless of whether you use pennies or paper clips, and regardless of whether you use coke, water, or oil?

I'm very surprised if that summarizes your observations; but if it does, then you are left with trying to explain why one of the objects turns darker black or turns black faster, or why one of the liquids causes that to happen more pronouncedly.

If I were you I'd probably get six clean bowls, fill two each with fresh liquids of the three kinds, and put a penny in one bowl of each and a paper clip in one bowl of each. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 5, 2010

i am doing a science project and I wanted to know what causes pennies to turn dark? What is the chemical make-up of lemon juice and of salt and vinegar ⇦in bulk on eBay or Amazon [affil links] ?

Rudy r [last name deleted for privacy by Editor]
science - Sacramento, California
January 19, 2010

Pennies don't rust because they have no iron in them to make rust occur.

bob willemhigner
- Cooperstown New York
February 1, 2010

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Rock Tumbler on Amazon (affil links) Yes, I have a purse full. I find them when I am out walking my dog. Maybe they don't rust but they rot. I took them to the bank and they told me to throw them in the garbage. I don't think that is fair. How do I clean the pennies and nickels and dimes up? Michele Hance - Hamilton, Ontario, Canada September 7, 2010 Hi, Michelle. Try a rock tumbler [affil links]. . . . which is basically a coffee can with a rubber liner that you fill with the coins and some corn cob grit and detergent, which you then put on onto a small motor that rolls it for a day or two. Good luck. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey October 26, 2010

I read through all the responses and Im sorry because this must be the 8th time someone has bothered you about this ted but I'm doing a project and I'm in 7th grade myself and I need a little more information for my conclusion. Can you go into a little more detail on how the acids in sodas react to the pennies and I mean the current ones

Neil V [last name deleted for privacy by Editor]
- Naples Florida
November 21, 2010

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Hi, Neil

Today's pennies consist of a zinc core that has been copper plated, so the zinc is not supposed to be exposed. The copper slowly reacts with oxygen in the air (and maybe a bit with sulfur in the air) to form copper oxides (and maybe copper sulfides), which tend to be brownish as opposed to the bright shiny orange color of a new penny.

Mild acids found in soda are generally not strong enough to actually dissolve bare copper, but they do react with the copper oxides, dissolving them into the soda as metal salts, and releasing water and some hydrogen gas. The usual acid in soda would be mild and dilute phosphoric acid, H3PO4.

I am a little reluctant to write the equation for the reaction because it could start a debate, but I think it is:

3Cu2O + 4H3PO4 --> 2Cu3(PO4)2 + 3H2O + 3H2

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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Hi. I'm a senior in high school, and I need to look for a science project. I remember doing this project a year ago, where I wanted to rust pennies (I know now that they corrode, not rust), and I was hoping to do it again, but I can't come up with any ideas. I was hoping for some inspiration or something. I'm considering corroding the pennies again, but with what...maybe Ill do a penny cleaning experiment...hmm. Any ideas?

Actually, I've noticed that pennies have a white rust like substance on them when they are really old. Is this a chemical reaction that pennies go through, and what speeds this reaction up?

Isaiah B [last name deleted for privacy by Editor]
- Larado, Texas, United States
December 9, 2010

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Hi, Isaiah. The corrosion products of copper are not white; they can be brown (as in old pennies) or green (as in old roofs and statues); but pennies after 1982 are zinc cores with a thin copper plating, and the corrosion products of zinc can be white.

Maybe you could sand the copper plating completely off of a post-1982 penny, and make a battery out of this penny and a regular penny stuck into a lemon and measure the voltage it generates. Then you could compare the corrosion resistance in lemon juice plus salt of a batch of pre-1982 pennies vs. a batch of post-1982 pennies, hypothesizing that the voltage difference because of the dissimilar metals will accelerate the corrosion?

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 9, 2010

Thanks for responding. Although I have already completed my science project, your idea with the battery sounds like something I'd like to try in the future. Thanks again for the idea, and god bless ^_^

Isaiah B [last name deleted for privacy by Editor]
- Larado, Texas, United States
December 13, 2010

What color is a corroded penny?

Norah J.
student - New Jersey
October 27, 2011