Please Help! Measuring the cleanliness of pennies

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I doing my science project this year and i'm going to be testing which cleaning solution cleans pennies the best but I cant figure out how to measure the cleanliness of them numerically.
Dominique

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Hi there!
This sounds like a really cool project!! Would you mind sharing some more info on how you will be conducting your experiment so I can better answer your question?

You could measure cleanliness in a number of ways. I think you will like the second one best with the percentages!
It could be:
- bacterial cleanliness
You could check to see which cleaning product makes the penny most clear from bacteria. To do this, you could possibly swab a penny with a sterile swab that has been dipped in sterile dH20 and inoculate a nutrient plate (agar petri dish) with what you have swabbed, and then count colonies and compare which plates have the least amount of bacterial growth and hence, which product cleans the pennies best.

- color or luster
You could use a penny's color or shine to determine which of the products worked the best.
I suggest reading this article that outlines what makes a penny shiny and the role that copper-oxide removal plays in how clean a penny is. You might find it helpful. https://www.scientificamerican.com/arti ... e-a-penny/
You could take pictures of the pennies and compare them with each other, however, this wouldn't give you a numerical value per se.

Another way to put a numerical value to it is to make up your own number scale. For example, you could pick the shiniest penny you can find and call it 90% bright. Find the dirtiest old penny you can, and call it 10% bright (Not 100 percent or 0% brightness because you might find a brighter or duller penny). Then you could rate their brightness as compared to your 90 percent and 10 percent samples. Then, you can carry out your experiment and rate the cleaned pennies by percentage brightness according to your scale. Now you've got numbers that you can graph.
You could even make a graph on a big sheet of paper and glue the actual pennies to it for a cool visual effect!!

Please let me know if you have any more questions and I'll be more than happy to assist!
Best of luck and happy sciencing!

Stay nerdy,
lmp1341