Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Cleaning copper pennies
USA pennies today are copper plated zinc. Try cleaning a penny by immersing them in a solution of 5% acetic acid ⇦this on eBay or Amazon [affil links] (that's vinegar ⇦in bulk on eBay or Amazon [affil links] , pinch of cream of tartar (my Webster's Collegiate Dictionary says it is used especially in baking powder and in certain treatments of metals), a pinch of table salt, and a drop of dishwashing liquid (sodium lauryl sulphate, probably).
Cream of tartar is used to help whip egg whites to greater heights; my cookbook, Joy of Cooking [on on Amazonaffil links], warns not to use it in the copper bowls preferred in French cookery for this purpose. The whites will turn green.
The same cookbook says that you can degrease plastic bowls with a mixture of lemon juice and vinegar. These bowls are degreased before whipping egg whites since the grease will inhibit the foaming of the whites.
Electroplaters know how oil sticks to polypropylene. I wonder if it is the terpenes in the lemon that are doing the trick. I'll have to get some lemon skins for my next experiment.
Tom Pullizzi
Falls Township, Pennsylvania
1997
I feel that the best cleaner for home plating is toothbrush and toothpaste. The mechanical action with the very mild abrasive serves to simultaneously remove both tarnish and light soils like fingerprints -- and it's about as "green" as you can get.
For heavier tarnish you can use a stronger abrasive like Bon Ami ⇦this on eBay or Amazon [affil links] or Ajax ⇦this on eBay or Amazon [affil links] .
If you start with a new, bright penny, clean it with toothpaste, zinc plate it using Tom's vinegar/sugar/epsom salt formulation, then 'buff' it with the toothpaste again, you will have produced a bright and adherent plate (adherent enough for a science class demo, if not for industrial use) without having used anything poisonous. It would be interesting to know the solubility of zinc in this solution and whether one could safely ingest a small quantity of it.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1997
Multiscrub, that soft abrasive cleanser, does a nice job, and leaves a water-break free finish. BTW, Ted's comment on the toxicity of home plating solutions reminded me that I had previously written on this subject. The following originally appeared in a finishing.com chatroom. I have adapted the story for the Hotline:
Recent experience with demonstrating electroplating to young people.
I brought my plating solution to show a 10 year old, and her 7 year old twin sisters. They were interested, as long as their little attention spans will allow.
The 10 yr old was first impressed with the glassware, clips, wires, stirring rods, beakers, etc. They were "cool" - unquote. Where did I get this "cool" stuff? So at least if you can't impress them with your brilliance, dazzle them with lab equipment.
I have been working on a plating solution that is made completely from items available in the home, and without using concentrated acids or bases. It is mighty tempting, I'll tell you, to augment my supplies from finishing houses which I visit. But I have resisted, and I have not resorted to using muriatic acid ⇦this on eBay or Amazon [affil links] or caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] . I was glad for this after my test with the nieces.
But at any rate, it is a MISTAKE to tell a kid that you made all these solutions from stuff in the kitchen. As soon as 10 year old heard this, she tasted the solution. Quick as a kid. Unstoppable. Sounds dumb if you are an adult, a beast of burden, or a baby rabbit, doesn't it? Not to a 10 year old.
I had also decided to use only low voltage batteries for the test. Benchtop Rectifiers would be nice in many ways, but again, I am glad that I am sticking with batteries, and will continue to develop my apparatus using a battery power supply.
As soon as we got started hooking up the cell to the penny, the 10 year old asked if she was going to be electrocuted by the 1.5 Volt, D-cell battery. When I said no, she tried to zap her sisters. I guess she figured: she couldn't kill her sister, but it would be funny to see her fly across the room.
So,
- make the solutions as nontoxic (and dilute) as possible
- don't mention the K word
- use batteries, and you have less to worry about. I can just (shudder) imagine what a little kid will think about when she sees rectifiers plugged into a wall socket. And worse than that, the questions you would have to field.
- kids seem to be aware that electricity and water don't mix. Hmm...This electroplating demonstration is going to be harder than I thought.
- Make EVERYTHING spill proof. Don't do anything remotely messy, like cleaning pennies on a sponge pad with: a. toothpaste, b. cleanser, c. vinegar, using: a. toothbrush, b. paper towel, c. rag.
- While we are talking spill proof: leads, wires, clips, etc. are being phased out of my equipment.
I am going to bus everything with either soft wires in tracks from here to there, or stiff wires in a bus.
I think kids should get to touch the equipment, they love that, but it is too easy to knock things over, especially when they start fighting for the next space in the plating cell. Unless you can do this demonstration outside. Then let them go at it, and stop the action by pouring a bucket of soapy water on them. This method also works on fighting dogs, but is much more effective on the animals, I mean the dogs. Just another reason to use low voltage. - If you say something you consider pithy, and the 7 year old doesn't share this belief, be prepared for a "duhh". Kids get this from television, which is why it should be banned in favor of the internet. (duhh)
- You need a plating cell which has its own source of illumination, built in. Kids and flashlights don't mix at all, unless you want to be blinded by the thing every 3 seconds during the entire show.
- Any thought about shaking the children is caused by your own inadequacy as a chemist and showman, so be prepared with a system that works.
The plating solution must work flawlessly every time, this includes the cleaning cycle. A few chemists from Technic came to the Garden State AESF branch with a gold plating demonstration for Family night a few years back. They did a fantastic job, and the kids went wild. Also, as Ted Mooney has observed, kids immediately grasp Faraday's Law when it comes to time in the tank and gold thickness. They also know shiny, complete coverage, and immediately compare their work to the others. If they see a discrepancy, you will be trying to plate all night. Their young lives will be hopelessly ruined if their sister has a shinier penny.
My test ended rather unceremoniously, as usually happens when you fail to keep giving the kids new reasons to look, and when the table got a little messy. Plating bright copper pennies with a blue, bright zinc plate in this demo was impressive, however flawed. The kids wanted to clean and plate all by themselves, and they enjoyed the process. Now I have to work on making it enjoyable for the adult, keeping the kids enthralled for as long as I want, and teaching some chemistry at the same time.
I think when I get my act together, I will take it on the road. I wonder if a substitute teacher could find happiness showing magic to kids all day?
Tom Pullizzi
Falls Township, Pennsylvania
1999
I am doing a science project on what juices clean pennies best. I have found citric acid ⇦this on eBay or Amazon [affil links] can clean copper. Could you please give me information on the decaying of pennies.
I NEED IT BY TONIGHT!
-TRACY
Tracy A. [last name deleted for privacy by Editor]Did you wait too long to start the project, Tracy? I'd guess that lemon juice cleans pennies best, since it seems to be stronger in acid than other juices are. Is that what you found? As for decaying of pennies, did you know that they actually consist of copper plating on a zinc core? Please see our FAQ: What Cleans Pennies Best -- it has all the info you need. Good luck!
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1999
I am in fourth grade, and am also working on a science project cleaning pennies! We have tried lots of cleaning agents, and found that fresh juices like lemon and grapefruit juice clean pennies fairly well, but vinegar with one teaspoon of salt was by far the best cleaner. Why would cream of tartar make it work even better?
What is the chemical reaction that is occurring? Why didn't red wine vinegar clean nearly as well as distilled white vinegar? I found one internet site that talked about oxidation and hydrogen ions being free to bind, which resulted in cleaner pennies...Can you help me understand the process that is happening?
I really appreciate any help or references you can provide.
Peter W [last name deleted for privacy by Editor]- Fairbanks, Alaska
1999
by Steve Spangler
on AbeBooks
or eBay
or Amazon
(affil links)
by Janice VanCleave
on AbeBooks
or eBay or
Amazon
(affil links)
My name is Keven and I am doing a big science fair project and 5 page report on what acidic household product cleans pennies best. I saw that all of these people have e-mailed you and I was wondering if you could tell me what you told them because I am new to the internet and don't know how to e-mail them. I really don't need the answer quite yet but if you could tell me where I could find different information for my report. THANK YOU, Keven
Keven F. [last name deleted for privacy by Editor]- Beaverton, Oregon
1999
Nobody answers these letters in private, Keven; what you see here is what you get :-)
I think the point of your assignment is for you to TRY some safe chemistry experiments. Stick with fruit juices, toothpaste, soft drinks, and vinegars and you won't have trouble. Do not try any other household products ESPECIALLY NOT bleach, ammonia, window cleaner, oven cleaner, Drano, or liquid plumber-- some of these can burn you right out of the container, or can release poisonous fumes when mixed with other stuff.
We've already said that our GUESS is that lemon juice is the best juice. So, now try it, and a few others like orange, grapefruit, pineapple, tomato, grape, and apple juice, and see what you learn.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1999
If you want to shine a penny coin...and perform MAGIC at the same time...drop a Penny in a glass containing "Coke" (c)...[yep...The Pause That Refreshes kind]. Set it aside...and check it in a week or so. Leave it set long enough and the Penny Disappeared! (Dissolved). Cleans the rust off car bumpers too. Hmm...wonder WHAT it does for a stomach? (Note This is not disparaging to a product of any kind...just natural Chemistry at work)...try it...ED
ED CherneyMay 23, 2012
Hi Ed. Sorry, but I think I have to bust that myth. Even vinegar working on a cut open zinc-core new penny took over a week to do much. Coke did almost nothing in a week, even on a penny I cut into pie shapes to let it get at the zinc core.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
You can clean copper pennies by soaking in hot sauce. You do not want to rub the pennies while the hot sauce in on them. Rinse first, after soaking, so you don't rub off surface.
C. Moore- Ohio
1999
See the FAQ on how to plate pennies for a school project. Remember that Nothing Succeeds Like Success, so don't waste too much time studying the subject and spend a lot of time experimenting, and recording your experiments in a notebook using lots of drawings and detailed descriptions.
Nothing will impress your teacher more than a notebook with the results of your experiment. You don't have to discover a new element, but you should be totally honest about the information you found during a search (like in reading these letters), and the results and experiments you made after reviewing the literature. Give references for what you found in your literature search right in your notebook, and separate it from what you discovered for yourself. That is the start of science. That is why you were given your assignment.
The start of failure in your project is when you take information that someone else found, and you try to pass it off as your own work. This approach becomes more enticing the longer you put off your assignment, and the closer the deadline date approaches.
If you ask for information, be sure to thank anyone that helps you. It will make it more likely that people will help the next student that asks for help. You don't have to make a big production out of it; just write a thank you email in the form at the bottom of this page, and we will post it in the same letter. Never give personal information to anyone on the internet. We expect that email addresses posted here are supervised and monitored by an adult guardian. Always tell your parents or guardians what you are doing on the internet, where you go, who you meet, who sent you email and why.
Happy science project!
Tom Pullizzi
Falls Township, Pennsylvania
1999
I HAVE BEEN TRYING FOR MONTHS TO FIND OUT ......
WHAT ACTUALLY IS SCIENTIFICALLY HAPPENING WHEN I IMMERSE MY PENNIES IN WHATEVER!
I NEEEEEEEEEEEEEEEEDD THIS INFO PRONTO!
Jenny s. [last name deleted for privacy by Editor]- Taos, New Mexico
2000
If you are asking what is happening when a penny dissolves, Jenny, the zinc of which it is made (underneath the copper plating) ionizes into a zinc 'salt'. Ionized materials have totally different properties than their metallic form. Table salt, i.e., sodium chloride, i.e., NaCl, for example, is sodium ions and chlorine ions and behaves completely differently than sodium metal and chlorine gas. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000
I'm doing a project on which juices cleans pennies the best. I was wondering, which juice really does? Also, I have to do research tonight on it, and I have no clue what to write. What's in the juice to make it clean the penny? Well thanks a lot for your help....but I really need this info and FAST!
Sarah E. [last name deleted for privacy by Editor]- Chesterfield, Virginia
2000
What juices did you try and what were the results so far, Sarah? I think that after you tell us the result of your experiment, you or we will be able to make some conjectures about "What's in the juice to make it clean the penny". Good luck!
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000
My daughter is doing a science fair project on what juices cleans copper pennies. We know that the answer is lemon juice, but she must also do a research paper. Can you provide some type of information in which we can use is this report. Your help will be greatly appreciated.
Thanking you in advance.
Donna Unruh- Sauk Village, Illinois
2000
This question has come up so many times, Donna, that we've created a cleaning of pennies FAQ.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000
I'm doing a science fair project.Its a grad standard . we have all these pieces to turn in at different times. Well I'm doing what cleans pennies the best.
HELP ME GET THROUGH THIS!
KAMMY S. [last name deleted for privacy by Editor]- MINNESOTA
2000
2000
After reading this page, and the FAQs it referenced, what questions do you still have, Kammy? Please express them in terms of what has already been said. Thanks.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Thanks your info helped
One last question, you did this test before right? How did you make sure that all the pennies were equally dirty to conduct a fair test!
THANKS
tiffany h. [last name deleted for privacy by Editor]- New York
2000
Hello, Tiffany. There could be invisible oils on some pennies and not others, or small variations in the copper purity, etc. The oxide that gives the dark 'aged penny' look could be thicker on some than on others. So I don't think there is a good way of PROVING the pennies are equally dirty just from looking at them. Rather, I'd rely on statistics, which in turn depends on randomness.
So what I would do is gather a number of pennies that looked fairly close in age and dirtiness, but I wouldn't kill myself that they be identical. If I was testing 4 cleaning solutions I would get about 20 pennies. Then I would mix the 20 pennies all up. Now with my eyes closed I would divide them into 4 piles. Resist any temptation to re-sort them after you have randomized them this way!
Then I would clean 5 pennies with each solution, rather than just cleaning one. Hopefully when you clean 5 in each solution and look at the stack of 5 you will see a conclusive difference. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000
What in certain liquids cleans pennies the best? I heard it had something to do with oxidation. If you could use "oxidation" in your response that would be great.
Thanks.
student - Washington, Ohio
January 7, 2008
Hi Leon. Suppose your teacher asked you how big a tank you need to hold a mixture of 1 gallon of water plus 1 gallon of oil? You know that the word "tank" means a container like an aquarium tank or a gas tank or an oil tank, and you would answer: "a 2-gallon tank". But if you never heard the word "tank" before with that meaning, and you believed that the word refers only to an armored fighting vehicle, you would be none the wiser for posting your question here and receiving the answer "a 2-gallon tank"; I can't even imagine the weird mental images you would draw up to try to understand the answer :-)
So you should always feel free to ask a question if you don't know the answer, but you should not ask a question that you don't understand, because then we're all just talking jaberwocky and you won't actually learn anything from the answer :-)
You need to have your teacher explain the question and the words in it so that you clearly understand what the question is. Sorry, and good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Note to students with science projects: Please see our
FAQ on Cleaning Pennies; it will tell you everything you need to know! 
what should my hypothesis be if I'm shining a penny? what should my conclusion be?
THANKS SOOO MUCH!
- riverhead, New York
February 16, 2010
February 16, 2010
Hi, Miranda. Either you did not yet read the FAQ or else you did not understand it so you need to talk to your teacher. If you do not understand what s/he wants you to do or why, and what s/he expects you to get out of this, sorry, but we really can't help with that part :-(
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 22, 2011
I'm a science teacher, and a favorite lesson of the kids is the cleaning of pennies, zinc plating them, and then turning the coating to brass by heating. I've got the science behind this pretty well in hand except for one thing that has me stumped.
I've been having the students clean pennies by putting them in a salt and vinegar solution (100 ml vinegar + 1 tsp salt). This cleaner works well most of the time, but occasionally the pennies get coated by this black residue instead, especially if many pennies are dumped into the solution simultaneously.
The black residue feels slightly greasy to the touch and won't be removed by putting the penny into a fresh salt and vinegar solution. Nor does it come off with toothpaste and toothbrush. I can't find anything about this black stuff anywhere? Anyone know what it is?
- Santa Monica, California, USA
Hi, Ray.
Pennies from 1983 and later are made of copper plated zinc. If the copper plating is compromised, the vinegar + salt can reach the zinc core, which is rapidly attacked. I suspect that this is the source of the black smut, and that the reason it happens when many pennies are immersed is both that the chances of a compromised penny in the batch are increased, and the heavier load can exhaust the vinegar (with no more acid, the zinc can't stay dissolved). Just my theory.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 25, 2011
May 19, 2012
Thanks Ted. It's a good idea, but it happens even with pre 1982 pennies. I'm still baffled.
On another note, Tom said in a post above that he plated zinc onto pennies for his nieces. Tom, could you share what the electrolyte solution was that you used? I'd like to do that in the classroom but can't ever get it to work right.
Thanks,
- Santa Monica, California, USA
May 22, 2012
Hi again. I suppose sometimes a penny could have some organic material on it that reacts with the vinegar. Have you ever tried cleaning the pennies with TSP or pumice before putting them into the vinegar & salt, and still observed the same problem?
Tom's electrolyte is in our FAQ, "How Electroplating Works". I've done it several times and it works. But a couple of things to note:
1. It's a very very thin plating and not bright; you have to polish it with toothpaste and toothbrush to get it bright.
2. You have to plate at 1-1/2 volts; any higher and it will probably produce a lot of black smut.
3. You have to go easy on the salt or epsom salt. If you make the solution too conductive, the "extra" current (exceeding the amount that can be used by the available zinc in solution) liberates hydrogen, which both causes a smutty deposit and neutralizes your vinegar.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I have used toothpaste but not pumice. Does it make a difference if the toothpaste is whitening toothpaste?
The zinc tips did the trick. Thanks, Ted.
- Santa Monica, California, USA
May 30, 2012
A. Hi Ray. The toothpaste is just a generic way of safely cleaning the pennies, and I don't think it matters too much what brand and type are used. I believe that whitening toothpaste contains hydrogen peroxide (which is an oxidizing agent), but I don't expect that it will significantly affect the plating. (Haven't studied it).
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 31, 2012
Q. Hi, I am doing this experiment using various liquids, and I am working on the independent and dependent variables. I came up with the same variables that were posted in the FAQ page, but my question is how exactly would I gauge "consequent cleanliness" in order to graph it? I was thinking maybe percentage removed by taking before and after pictures and comparing. What do you think? Any help would be appreciated. Thanks!
John Harandow- Jacksonville, Florida, USA
September 9, 2014
October 2014
A. Hi John. There are quantitative ways of judging cleanliness, like particle counters that are used in "clean rooms", or reflectivity meters, etc. If you can find a free or inexpensive "light meter" app for a smartphone, it just might be vaguely possible to measure reflectivity. I don't want to suggest that such a thing is actually practical, but I also don't want to discourage you from looking into it ... so look around and make a judgement whether it seems at all practical or not.
Assuming that actually measuring reflectivity isn't going to work, then a practical answer for a student would probably be to use somewhat qualitative measures, like assigning a rating of 9 to what you "feel" is the brightest of pennies, and a rating of 2 for the dullest (I would not use 10 or 1 because you might someday find a brighter or duller penny). Taking photos to support your assessment sounds like a good idea.
I wouldn't use the term "percentage removed" because that introduces another variable (the original "dirtiness"). Instead I'd look for a group of pennies of virtually the same dullness as the starting point, and try to randomly pick 5 pennies for each liquid and average your rating, and graph the average for each liquid. Best of luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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