Fruit – Polishing Pennies (Weekly Unplugged Project)

By , September 29, 2008 3:53 am

This week’s Unplugged Project theme was fruit.  We tried a really cool fruit project that was less than successful.  I would have posted about our failure, except that I KNOW it can succeed since I did it successfully as a child.  It needs a bit more fiddling (so we’ll keep working and post when it is perfected).

Instead I’ll post about a fruit science project from our book 730 Easy Science Experiments: With Everyday Materials.  My oldest daughter found this in the book last week and for some reason was desperate to do it: polishing pennies. (I reviewed this book here if you want to know more.)

The idea is to show how lemon juice (very acidic) can clean the oxidization off a grungy old penny. If you live outside the US, any copper coin will work for this.

We ratcheted this one up.  I had always heard that Coca Cola was acidic enough to strip enamel off teeth and polish stainless steel sinks, so a comparison test seemed in order.  I had a Coke in the fridge from leftover guests so we gave it a go.

I was hoping that the Coke might perform up to the standard of the lemon juice and prove once and for all that it is BAD for your teeth.

Here are the ingredients:

Squeeze the lemon (pretty fun):

Put some lemon juice (and some Coke-if you choose to try the comparison experiment) into separate bowls and drop pennies into each bowl:

Leave them for 15 or 20 minutes then remove and compare:

We probably should have kept a “control penny” for comparison (actually, you can see the originals in the “ingredients” photo) but trust me, the lemon juice pennies were like new!  The Coke pennies only slightly shinier.  So much for my anti-Coke campaign.


What did you do this week for fruit? If you joined in this week’s fruit project, then please leave a link to your project in Mr. Linky below. If you want to learn how to join in the Unplugged Project, then please read more here.


Next week’s Unplugged Project theme will be:



14 Responses to “Fruit – Polishing Pennies (Weekly Unplugged Project)”

  1. Berry says:

    The coke won’t work to remove the patina from copper, but it WILL remove rust from bolts, etc. Try that with a comparison of lemon juice!

    Another example you could have used for the penny experiment is tomato ketchup. It works exactly the same.

    Berrys last blog post..I Love My Cat

  2. Linds says:

    Fun experiment!

    Lindss last blog post..Unplugged Project: Fruit

  3. I was under the impression that Coke would do the job too. There’s a lot of coke myths posted at Thanks for sharing all the fun science.

    Julie K in Taiwans last blog post..Art Lesson – Henri Matisse

  4. Heather says:

    We actually have this book to. It has lots great projects. This one looks like lots of fun that you did.

    Heathers last blog post..Fuzzy Caterpillars

  5. Meg says:

    E will really enjoy cleaning her coins. Thanks for the great idea!

    Megs last blog post..Unplugged – Fruit

  6. Nature Mama says:

    I thought that coke was able to eat a penny up to nothing, good think you disproved that *grin*. Fun experiment!

  7. Ashley says:

    What a cool science lesson.

    Ashleys last blog post..Unplugged Project~Fruit

  8. Alicia says:

    We’ve done the same experiment but last time we tried a whole bunch of solutions, from orange juice to ketchup to baking soda & water to milk. The kids hypothesized first about which ones they thought would get cleaner and then we compared. There were a lot of surprises! Milk did a pretty good job of cleaning, for one! We left ours overnight but we’re going to try it for a shorter time period too. It’s fun, huh? :)

    We made watermelon playdough this week for the fruit theme. Thanks for a fun challenge, as always!

    Alicias last blog post..Watermelon Playdough

  9. I think I saw on someone’s blog where they took a baby tooth and left it in coke for many DAYS. The tooth was majorly decayed.

    Great way to work in fruit! Fun project and very educational ~ even for us “old folks”! :)

    Becky@BoysRuleMyLifes last blog post..Fruit – Unplugged Project

  10. shawna says:

    Awesome! I think as I kid I did this project with a vinegar solution. I like how you compared the two techniques!

    shawnas last blog post..Unplugged #5: FRUIT!!!

  11. Michelle says:

    I think my kids would enjoy cleaning money… of course a couple of them still tend to put coins in their mouths… maybe in a few years ;).

  12. We have rejoined the project!
    We did this penny experiment in Kiddo’s science class a while ago using vinegar. He was a little young at the time, maybe we should give it a go again.

    Mom and Kiddos last blog post..Free Books at the Library

  13. Gerky says:

    What a great science project! We will have to try that.

    This week we made shrunked apple heads. You can find it at

    Off to think up a project for next week!

    Gerkys last blog post..Unplugged: Fruit

  14. […] week’s Unplugged Challenge theme was fruit. We have been doing so many things with apples over the past few weeks (you can […]

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