If you stick an egg in vinegar for a few days, the shell will dissolve and you’ll be left with a shell-less egg (as shown in some Instructables projects, like this one). How does this work? The eggshell is made up of calcium carbonate, and this can react with acid (e.g., vinegar) to dissolve and make some carbon dioxide bubbles in the process. Not only do you end up with a fascinating product, but the fizzy chemical reaction is fun to watch too. (This is also the same thing that happens with limestone rocks to create sinkholes.)

But there are some other neat things you can do using this reaction besides creating a shell-less egg. For example, if you “protect” part of the shell from vinegar, then it won’t dissolve while the surrounding shell does. The tricky part is finding something that sticks well to the eggshell and doesn’t dissolve in acid (i.e., vinegar). After playing around some, I found that fingernail polish works well for this. So, this means you can decorate an eggshell with nail polish, leaving parts un-coated that you want to dissolve, and then it effectively “carves” out the un-coated parts of the shell when the egg is dunked in vinegar.

You could carve eggshells into all sorts of patterns/shapes using this approach (which I’ve never seen used before). In this Instructables project, I used this approach to create a votive shadow lamp (it's also what may be sometimes referred to as a lamp projector). So, if you’d like to make a super easy, inexpensive, and attractive-looking votive shadow lamp mostly using materials you probably already have around your home, then this Instructables project is for you!

Step 1: Materials You'll Need

You just need some simple, common household materials plus a small light source to make your very own votive shadow lamp:

A raw egg
A pencil
Fingernail polish. The more pretty, bright colors the better. I ended up just buying a cheap assortment at the grocery store.
A cup the egg can fit in
Vinegar
A small LED light source. I used these LED lights from Amazon.com for this project, but others should work as long as they’re small enough (or the LED sticking out is small enough) to fit inside of the eggshell.
If you’re using the Amazon.com LEDs, you’ll also want a bottlecap. If you’re using some other light source, you’ll basically want something you can use to draw a circle around the base of the egg that’s big enough for your light source to fit through. See the steps below for details.
White school glue (to attach the light source to the eggshell). Other glues, epoxies, etc. would probably work too.

Step 2: Plan the Lamp's Base

Figure out how large the opening at the bottom of the egg needs to be for the light source to fit through it. For example, if you’re using the LED lights from Amazon.com, you could plan on making an opening that’s about the same diameter as (or slightly smaller than) the diameter of the light fixture, and then have the eggshell rest on top of the fixture (with the LED going inside of the eggshell).

These LED lights have the same diameter as a plastic bottle cap, so it’s easy to place the egg in a bottle cap and draw around the bottle cap to mark where the opening should be. See the pictures for details.

Step 3: Plan Your Designs

You can use a pencil to draw the designs you want to make right on the eggshell. I found it helpful to use a plastic bottle cap as a stand for the egg while doing this. Don’t worry about making any mistakes – you can rub off incorrect marks with a damp cloth, and you will not see any pencil marks when the lamp is all done anyway. You could think about any themes you might want for your shadow lamp – I tried a mix of nighttime/celestial symbols and other shapes. Even small details (like small rays/dots around the sun) came out well.

Step 4: Decorate With Nail Polish

To make the designs you drew be “carved out” of the eggshell, they should not be covered with nail polish. (Remember, the nail polish protects the shell from being dissolved.) I recommend starting by carefully outlining the designs with a layer of nail polish. (Also do this around the base opening that you drew in step 2.) It doesn’t matter what colors you use – just have fun decorating the lamp!

After the designs are outlined, you can fill in the spaces between them with more nail polish. As you do this, you can skip coating any other spots that you’d like to have carved out – for example, I created some rays/dots around the sun at this point. Be sure to let an area dry before adding another layer onto it.

Ultimately, all of the nail polish-coated areas should end up with two to three layers of nail polish. This will really protect the coated areas from being dissolved in the vinegar, and it adds some strength to the eggshell.

Step 5: Dissolve the Designs in Vinegar

When the nail polish on your eggshell is completely dry, put it in a cup and cover it with vinegar. Within a few minutes you should see the un-coated parts of the egg bubble as they start getting dissolved away. (The acid in the vinegar is reacting with the calcium carbonate to dissolve it and make carbon dioxide bubbles.)

After about 24 hours, carefully pour off the vinegar and add fresh vinegar to the cup, again submerging the egg. Before you changed out the vinegar, you should have seen a lot of bubbles on the surface of the liquid – mine were clearly in the shape of the heart that was facing the top of the cup! Pretty cool.

After about another 24 hours, your egg should be done! Carefully take it out and inspect the designs to make sure they’ve been “carved out.” (If there’s still some eggshell left, try leaving it in the vinegar for another 24 hours and that should do the trick.) Over a cup or bowl, carefully cut open the membrane that’s holding the raw egg inside still – it should easily spill out. Then carefully pull out the white, rubbery membrane. Carefully rinse the eggshell with some water and let it dry.

Interesting side note: I tried this with a hollowed-out egg but it didn’t work well because the vinegar dissolved all of the shell, leaving it a shapeless husk. When you use a raw egg, as is described in this Instructables project, the egg actually expands in the vinegar, and so it pushes against the un-coated areas and prevents vinegar from getting inside the shell and dissolving it from the inside out. Neat stuff.

Step 6: Admire Your Awesome Eggshell

Check it out – you just chemically carved an eggshell! It’s amazing what detail you can get from this process. If you have any cracks, you should be able to fix them with a little more nail polish. I only had one minor cracked area (see the pictures) – I easily patched this with nail polish, and you could only tell if looking on the inside of the shell.

Step 7: Attach the Light & Enjoy the Show!

I was able to set the eggshell on top of the LED light fixture and they fit together perfectly. I used a little white school glue to hold the shell in place and this worked fine for me. (If you want something sturdier, you could try other glues, epoxies, etc., that work with plastic or whatever the material of the fixture is.)

Turn on the light and enjoy the show. Take it to a dark room and watch it project detailed shapes onto the ceiling and walls. Check out the videos and pictures in this step for what mine looked like.

Enjoy your shadow lamp and show it off to friends and family!