Giving Copper Coins a Brass Layer

In this project we are going to go over my favorite copper alloy ~ brass. Brass is an incredibly interesting metal because it is one of the only alloys that has been around since pre-history. This means that before written records of the world were kept, brass was being utilized to help build stronger tools. Brass is a mixture of copper and tin; however, there are many types of brass that contain other metals as well. The type of brass can also change depending on the composition of copper and tin that is used.

Today we will be making a brass coating on a penny and a copper coin I got from the statue of liberty. The specifically cool thing about this coin is that it is the same thickness as the actual statue of liberty.

This project is commonly taught to highschool students, so with proper precaution this project can be done at home. This project is overall a three step process that can be completed in less than 2 hours.

Preparation Time: 20 minutes

Project Time: 45 minutes

• Proper PPE (gloves, goggles, close toed shoes)
• Zinc Chloride (or sodium hydroxide)
• Any zinc metal (zinc oxide, zinc pieces or mossy zinc)
• Distilled water
• Vinegar
• Table Salt
• Copper pieces
• 2 Beakers (they need to be heat resistant)
• Heat source
• Torch
• Tongs
• Paper towels

During this project, it is a must that you wear gloves and wear goggles at all times. Gloves protect your hand and the penny from oils on your hand and goggles protect your eyes from the chemicals we will be using in this project.

Cleaning the pennies of oils and oxidation is important because the reaction will be less effective on a dirty penny. This step is simple and we add in an amount about 100mL of vinegar with 3 grams of NaCl or kitchen salt.

From here we just add in the pennies into solution for 5 minutes. Once you take the pennies out of solution, clean them with a paper towel or cotton swab. Your penny should now be shiny, and if it isn't, clean it again with this same step.

The solution eats away at the copper oxide and oil that is on the pennies. Vinegar is also known as acetic acid, which usually comes in concentration of around 3-5%. Stronger vinegars are sold, but they should be diluted down to this strength so the acid doesn't start eating away at the copper layer of the penny.

In my video above, I leave a penny in solution for a week and when I came back I could easily poke a hole through the penny.

For this step you will need to make a 1M solution of zinc chloride, to do this you add in about 17grams of zinc chloride powder with 100mL of water into a beaker. This can be scaled up or down, however keeping it at a 1M solution is only semi important. The solution will need to be hot for everything to dissolve, so I put the beaker on a hot plate and wait for everything to heat up.

Once heated up take the 1M solution of zinc chloride and add in about 3-8 grams of zinc pieces. The cleaner the zinc the better, which means if your zinc is oxidized, the pennies will have a zinc oxide layer instead of just a zinc layer. This causes the pennies to not be as shiny as others.

Now the solution is ready to add the pennies!

This step is fairly simple, yet it feels like it takes the longest.

We will add in our pennies to our hot zinc chloride solution and wait until they get a nice silver zinc coating on the outside. I ended up flipping my pennies over about half way through to make sure both sides were being coated evenly. My pennies took anywhere between 10-20 minutes to coat the entire penny.

The trick in this step is to make sure all the pennies are touching zinc pieces, but not touching other pennies.

This works due to the zinc and copper starting to share electrons with each other and they start to chemically bond.

Once the pennies have a zinc coating you can pull them out, dip them in distilled water followed by drying them off with a paper towel. Make sure to not touch them with your bare hands because the oils from your hands can still make the reaction less effective.

This part involves using fire to melt the layer of zinc into the copper layer of the penny.

I use my propane torch, and it just requires 4 seconds of direct heat. This reaction takes place very quickly and is amazing to watch. I even provide a little slow motion of this happening in my video.

After the penny turns a beautiful golden brass, make sure to dip the penny into some water to cool it down. From here this will slow the melting of the zinc and brass and the color of the brass will really start to shine.

This happens because zinc melts at a very low temperature compared to copper, however there are a lot of ideas that come into play when making alloys. We are able to melt the zinc into the copper because molecularly they are very similar sizes. Copper atomic mass is 63.546 , while zinc's atomic mass is 65.4. This alloys the two metals to bond under easier conditions, which is why it was one of the first alloys.

THIS STEP INVOVLES THE USE OF OPEN FLAME OR HOT PLATES.

Please be care if trying this at home. I feel very comfortable personally with this project, though I always make safety my number one concern.