Hi! You only need three simple ingredients to make gemstones that look pretty realistic.

It's a bit of a messy project, but cheap and simple. No polymer clay, no resin or other more expensive materials are needed.

Supplies

paint (acrylic paint or other)
cornstarch
school glue (clear or white)
recycled containers/cups
something to stir - popsicle sticks, toothpicks, etc.
silicone mat or aluminium foil
optional: latex gloves
optional: clear nail polish

Step 1: Make the Clay

We’re starting with paint. I’m using acrylic paint, but other paints work too.

Put it into a recycled container and next add some cornstarch. The last ingredient is school glue. Clear or white glue - it doesn’t really matter. Add it to your mixture until it forms a dough.

I’m not measuring anything - just add more cornstarch when it’s too sticky, more paint for more color or more glue if it’s too dry.

Now comes the messy part. You don’t have to wear gloves (acrylic paint doesn’t normally stain), but then you have to wash your hands a LOT. And I realized gloves just look much better on camera ;)

Step 2: Color Combinations

Knead the dough until it’s an even consistency and make two more colors, a light one and a dark one.

The color combinations are important for how realistic the gemstones will look.

Ironically, the combination I took the most pictures of (3rd picture) looked less realistic.

The first one looked similar to malachite, the second one created nice dark blue stones.

The ratio of every color makes a difference too.

Step 3: Mixing the Colors

This clay dries out quickly, so I have water next to me to hydrate it.

Now you just need to smush the colors together. I like to hydrate the clay well before I do that, since adding water later on can mess with the nice marbling.

Mix the colors however you like. I like to break up the clay because that creates interesting patterns.

Just keep going until you think the pattern looks natural. But don’t overdo it or everything will blend into one color.

Step 4: Shape and Let Dry

Then create shapes of your choice. The clay is quite soft, so you have to keep the shapes very simple. I place them on a silicone mat, but aluminium foil works well too.

Holes can be added with a toothpick, which is useful for making jewelry.

Let the stones dry overnight and turn them over if the bottoms aren’t dry yet.

You can sand the stones if you want to change the shape a little bit.

Step 5: Store-bought Vs. Homemade

As a comparison, I mixed acrylic paint with store-bought clay, and the results were less vibrant than the homemade clay.

Especially with dark colors it makes sense: Clay is normally white, so you have to add a lot of black paint to get a nice black color.

In general, I felt like more paint was needed for store-bought clay. And it was just as messy. The consistency of store-bought clay is probably better to work with though. So it's up to you what you use!

Step 6: Glaze

Now the stones look a bit matte and less vibrant. We’re going to glaze them because it makes them look polished.

My favorite option is using clear nail polish. With just one coat you get a very glossy finish.

Instead, you can also use the same glue you used for the clay. One coat will make the stones slightly more shiny and the more coats you add, the shinier it gets.