Introduction: Sea Urchin Skeleton From Clay: Display or Jewelry Purposes

About: Clay and Jewelry Artist; All-around Creator

Sea Urchin shells, or skeletons, are interestingly beautiful. They are also as fragile and prone to breaking when handled. In this Instructable I will show you how I made a sea urchin skeleton out of clay that could be used for either jewelry or display because it does not have the fragility of an actual sea urchin skeleton.

I will include tips on using air dry clay at the end of this Instructable. If you have ever wanted to try air dry clay, I highly encourage it.

*For Polymer Clay Artists:

As I work with air dry clay, I am not extremely familiar with polymer clay because it is not my medium of choice. That being said, if you want to make this project with polymer clay I encourage you to read through all the steps so that you can best determine when you should bake your creation.


I have included links to Amazon for some of these supplies if anyone is interested.

1. Mat for workspace (you could use a plastic folder, plastic cooking mat, or a plastic clipboard)

2. White Clay (I use air dry clay, but you could use polymer clay as well. My air dry clay is homemade.)

3. Clay tools (a roller, a knife, a stylus, a ball tool, and a needle tool *The most necessary tools are the roller, the knife, and the needle tool as the knife or needle can substitute for the stylus tool if used carefully)

(At the time I posted this link, they said it was "unavailable", but the photo can at least give you an idea of what to look for.)

4. X-Acto knife or other sharp craft knife

5. Cotton balls (I used three)

6. Reference photos (I have included some on this Instructable that I obtained through Unsplash and Pexels, and Pixaby. These websites offer photos that are FREE for commercial use)

7. Chalk pastels for coloring (I am using a pale peachy pink, a dark magenta pink, and a purple, but you can use whatever colors you want)

( I put these chalk pastels because they seem like they would be good. Mine have been out of a package for years, so I don't know what they are!)

8. Triple Thick or another dimensional glaze (you could also use liquid clay)

9. Water (for smoothing air dry clay and keeping it workable throughout the process)

10. Small paint brush for applying pastel coloring

11. Light brown acrylic paint (I am using 'Butter Pecan' by Folkart)

12. Foam mat (optional, helps air dry clay dry evenly)

13. Vinyl gloves

(I didn't use gloves, but I highly recommend them after making several of these. Wearing them while coloring the piece with the pastels will make you not leave fingerprints, so they would be a really good idea)

Step 1: Preparing the Base of the Sculpture

First, I took my three cotton balls. These were just regular sized cotton balls, not the jumbo cotton balls. They would become the core of the sea urchin skeleton. After my clay has dried, I can remove the cotton center and it will be a hollow sculpture (this is the same principle that many polymer clay artists use when making hollow beads, which is where I got the idea!)

Taking one of the cotton balls, I unraveled/unrolled it. I spread the fibers apart a little bit with my fingers. I took the other two cotton balls and placed them on the unraveled cotton. I folded the unraveled cotton over the two cotton balls, first one side and then the other.

After that I simply began squishing the whole mass as tightly together as I could so that the fibers would contract and form a stiff wad instead of a light, fluffy ball of cotton. I pinched and rolled the cotton in my hands until it was about the size of one of the original balls of cotton, but it was much denser. I set it aside.

Step 2: Covering the Base

The cotton base is made and now it must be covered with clay.

I got my clay and rolled it into a thin sheet with my roller. The sheet shouldn't be too thin (not paper thin!) because it will break too easily when you try to put it over the form. My clay sheet is about the thickness of a wooden popsicle stick, or about 1/8 of an inch (or 0.32 cm, about).

*And, hey, if it breaks, you can just roll out another, thinner sheet of clay and wrap it over top of the first one. I have done that on one that I made and it worked well.

I placed the cotton wad in the middle of the clay sheet. I folded the clay sheet in half, encasing the cotton wad in the fold. Using my fingers, I pressed down on the clay all around the cotton wad, closing the clay as you would when sealing up a pie with pie dough.

Once the cotton form was fully closed in the clay, I trimmed off the excess clay. It kinda looks like a little apple dumpling. If you accidentally cut too close and open the form, just poke the cotton back inside with a stylus tool other stick-like tool and then press the clay back together. I have done that, too!

I rolled this little clay dumpling in my hands to smooth out the trimmed edges. Squishing it with my hands gave better results than rolling, however. When it was uniformly smooth, I took my ball tool and used it to further smooth out the little cracks and flaws. If you don't have a ball tool, you can use your finger. If there is one stubborn spot that insists on being a hole/crack, don't fret. You can use that hole as a starting point for the hole that will be made later on. The side with the hole will be the bottom of the sculpture.

Step 3: Taking Shape

All the little cracks were smoothed out now, so I started on the shape of the sea urchin shell.

After I decided which side would be the top and which side would be the bottom (mainly because I had a small hole), I pressed the clay lump onto my work surface, pushing the edges with my fingers to make a flattened gumdrop shape. The rounded part is the top, the flat part is the bottom.

Taking my knuckle, I pressed it into the middle of the bottom of the form to make an indentation. I furthered this indentation with my thumb. Next I took my ball tool to make the sides indent. Sea Urchin skeletons have a five pointed star shape on them, and at every one of the stars' points the skeleton is slightly sunken in. To do this I used the ball tool to press on the bottom and a bit of the side of the form in five places. I didn't want it to be drastic, so I rolled the ball tool in and out of the indent so that it was a gradual curve, not a sudden drop. These little "ditches" on the skeletons are not evident unless seen from the side, so they shouldn't be too obvious.

I slightly flattened the form by just pressing down on it with my finger.

On the top of the clay form I poked a little hole with my stylus tool. I DIDN'T GO ALL THE WAY THROUGH. This was only to make the dip in the top of the skeleton. And if you do go all the way through, it's fine.

(I have added the little illustrations to the photos to help illustrate the shapes I am making. Because I want them to be subtle, I realize that they may not show very well in some of the photographs, so hopefully the illustrations will clearly show what I mean.)

Step 4: Patterns on the Surface

Sea Urchin skeletons have interesting patterns on their surfaces. The most obvious is the little holes running down their sides in triangle formations.

Taking my stylus, I lightly traced little triangles down the sides of the form. The point of the triangle is at the top and it gradually widens as it goes down to the bottom. These triangles are the same place as the little "ditches" made in the previous step. There are five of them, looking like a starfish on top of the shell. These are only guidelines for where the holes will be placed later.

The second most obvious design on the sea urchin skeletons is a zigzag pattern going down the sides in between the triangle formations. These zigzags are on the larger sections that are left between the smaller triangles. I used my stylus and my knife, so you could just use a knife if you don't have a stylus. Try to make the zigzags pretty small.

Remember: Be light in all of your tracing. These little patterns are not holes in the skeleton, they are simply small crevices.

Now there should be five little triangles and five zigzags in between the little triangles.

The last pattern in this step is a honey comb type pattern that runs between the zigzags. Using my knife, I carved a honey comb pattern with the zigzag being the middle. Don't carve the honeycombs in the triangle spaces. Leave those blank. I included an illustration to help you understand the "honeycomb" pattern, as I call it.

Step 5: Color

I gave my sea urchin shell a base coat after this step. With my X-acto, I carefully scraped off a little bit of my peach pink chalk pastel onto a plastic lid. Using a small paintbrush, I brushed the chalk onto the surface of the clay. (P.S: if you are working in air dry clay and find that nothing is sticking, squirt your sculpture with a very fine mist of water. Don't drown it, just a squirt or two will do. Let it sit until the water has been absorbed and the clay is not tacky, then proceed with coloring.) I was very light in this application because the color will darken as the clay dries.

Taking the magenta colored chalk pastel, I scrapped off some with my knife and then applied it to the sides of the little triangles. Now the star on top of the shell is very visible.

Still with the magenta pastel, I lightly brushed it on the zigzags and very lightly over the entire rest of the surface. The darkest portion should be the triangles.

I gave the triangles a very light coat of the dark purple, too, using the paint brush. The color lines shouldn't be too stark, try to blend the pastels to make the lines more gradual and natural looking.

I scraped some plain brown pastel onto a plastic lid and once again went over the triangle pieces. We are gradually building up colors here. With a very light hand, I brushed the brown all over the entire sculpture just to give it a slight earthy tint. The triangle shapes should still be the darkest portion.

I ended up going back and doing another coat of the brown, but it is personal preference really.

I set the sculpture aside to dry. Since I am using an air dry clay, I have to wait on that, but if you are using polymer clay this would probably be where you would bake it. Since this is a hollow sculpture, I would probably leave it for two to three days to be on the safe side ( I tend to stay "on the safe side" with all my sculptures even if they would be dry before that time).
If you have a foam mat (like is used for stuffing pillows), set the sculpture on that to dry. This helps it dry evenly because the surface of the foam is porous and allows air to get through. If you remember to, you can go back and flip the sculpture over after a while, but I didn't remember to.

Step 6: Punching Holes

Now that my sculpture is dry, I am gonna punch holes in it! AAAHHH!

Ha, no, seriously, I am gonna punch holes in it.

Most Sea Urchin skeletons that I have seen in photos have two holes in the structure. The hole on top is the smallest. With my X-Acto knife, I cut out a little hole in the top of the form, making it a rough "star-ish" shape. It is somewhere between a circle and a five-pointed star.

On the bottom I cut out a similar shape, but it is larger. Then I pulled out the cotton. Wha-la, it is hollow.

The cotton might be a bit tricky to get out, and there will probably always be a bit of fuzz on the inside, but I am going to put varnish over that, so I don't care. Just go slow and careful, and most of it will come out pretty easily. You could use tweezers if you have a hard time getting some of it out.

Also, you can reuse this cotton for either making more of these or making some other type of hollow sculptures. I have reused this same cotton several times now.

With my needle tool (which is actually an oversized pin), I punched tiny holes down the triangle shapes that I made earlier. I made two rows on each line, so each triangle has four lines of holes total. I made sure to go all the way through so that these weren't just surface marks.

So, I would advise to wait on pulling the cotton out until after you have punched the holes with the needle. It is so much easier. I did part of this one without the cotton inside it, but the form wants to squish kinda as you push the needle in it and you risk poking your fingers more. I just stuffed the cotton back inside and continued punching holes.

Step 7: The Little Dots

Sea Urchin skeletons have little knobbly bumps all over them, and to recreate that I used Triple Thick (a dimensional glaze) mixed with a tiny bit of caramel colored paint. Most of the photos I have seen the bumps appear to be brown, so I went ahead and made mine brown, too, but some I have seen are white, so feel free to use whatever color you want.

*If you don't have Triple Thick, liquid clay would also work.

Taking my needle tool, I dipped out just a tiny bit of the Triple Thick (this huge jar is gonna last me next to forever at this rate). Using the FolkArt Acrylic paint "Butter Pecan" I dipped out a teeny weeny bit and mixed it thoroughly with the Triple Thick. I didn't want it to be totally opaque, so I only used a little bit of paint.

I dipped some of the mixture onto the needle tool and then used it to make the little raised dots on the surface. I let the mixture drop onto the clay, then I pulled the needle back up, creating a little blob. On the sections with the zigzags there are generally two rows of dots on either side. However, they seem to be placed rather randomly, so photos are your best bet for "accurate" placement. Honestly I don't think that anyone will notice if you place them wherever. Small dots, medium size dots, and large dots are all good. The sizes of the dots seem to be a mixed lot.

Don't do the dots on the bottom until the ones of the top have dried. Otherwise you are just going to squish them with your fingers while you put the new ones on. A cool way I found to set the form to dry was that I stuck it on top of a glue bottle. It fit perfectly and could stay there and dry without applying weight to any of the wet dots.

To keep my Triple Thick mixture from drying out while waiting for the first dots to dry, I shut it in a little plastic box with a lid. I have had this generally work for glues and paints, but sometimes for unknown reasons (weather?), it doesn't work as well. If your batch gets too tacky and thick for using, just add a tiny bit more Triple Thick and mix it back up. It should be good to go.

The Triple Thick takes a pretty good while to dry. I had one shell that I made that I let sit overnight and thought it would be dry the next morning. I had already put all the dots on it, so I was just waiting for it to all set up really good. It wasn't completely dry the next morning; sitting it on a table the weight of the form squished a few of the dots on the bottom. Just a warning to let it dry much longer than you think. It is the third day for that sculpture and it seems fine now.

Step 8: Finishing Up

Now you can varnish your project and it will be done!

I wish I had a matte varnish, but I don't. Matte would be perfect for this project. If anybody has any suggestions on a good matte varnish for clay, please post it down in the comments. I have tried Varathane Matte and it wasn't good. It peeled.

Anyway, sadness aside, I have Duraclear Satin varnish that I am gonna use on this.

The Duraclear Satin varnish is a non-toxic polyurethane varnish. It and Duraclear Gloss are what I use for all my projects that I varnish. I have been pleased with it. It is a brush on varnish, so I just apply it with a soft makeup brush. You should varnish the top first and let it dry then varnish the bottom and let it dry. You should also varnish the insides. I generally do three coats of varnish, putting on each coat after the first one as dried (it says on the bottle something like an hour).

Step 9: Finished Product

Here is just some photos of the finished product. I think they look pretty good, and of course there is room to improve, but there always is!

I made one into a necklace using a simple lark's head knot. This link will take you to a great tutorial by Rena Klingenberg on how to do that :

The smaller shells are made using about one cotton ball for the form.

Step 10: Air Dry Clay Tips

So I said I would give some air dry clay tips and here they are.

1. Water can be used to smooth air dry clay.

As the clay dries, it can become hard to work with/color. A mist of water can help restore the ability to put in surface details without compromising the clay's strength. Don't douse it in water, though, because then you will risk compromising the clay strength.

2. Tools don't have to be expensive.

Some people will recommend you to get really expensive clay tools, but you can actual do a great deal of work with inexpensive tools. The set that I included the link to in the supplies for this project are my favorite tools even though they are inexpensive. I have actually seen some people call them not very good or pretty cheap in quality, but I don't think so. I have accomplished many things with these tools that show me that it does not matter if the tools are expensive.

3. A good air dry clay doesn't have to be expensive either.

I make my own air dry clay. It costs me around $2:00 US dollars to make a batch that is about the size of a regular sized soup can (that is my math from how much of each ingredient I use vs how much that amount of that ingredient would cost). I can't put how many ounces it is because the clay is extremely light, so that wouldn't give a good idea of size. I think that is a bargain. There are many cold porcelain clay recipes on the internet, including a few on this site.

4. Dry on foam mats to reduce cracking

Air dry clay cracks are often due to a few things. One of these is that it cracks as it releases the moisture inside it. That often can't be helped, but a big reason it cracks is due to not drying evenly. By placing your creations on a foam mat they will dry more evenly due to the porous surface of the foam allowing air to circulate around the clay.

5. Use plastic tools

I have found that plastic tools (as much as I don't really like plastic) are the best for air dry clay because they don't stick. Metal and definitely wooden tools will stick to air dry clay. Plastic mats will help the clay not stick when you roll it out because there is nothing more frustrating than rolling a thin piece only to have to scrape it off the surface and start over.

6. Use aluminum foil or other things for armatures for larger figures

Air dry clay needs armatures for large figures. Aluminum foil crushed together to make a tight wad can be armatures. Clay can then be spread over the foil, but make a thicker layer than you think you need because air dry clay shrinks and if the layer isn't thick enough the aluminum foil will start to poke through.

7. Don't give up on your first batch!

If you decide to make cold porcelain clay at home, don't give up on your first batch! I tried two different recipes before I found one that finally came together. It was so frustrating. I threw out two batches in disgust. Finally I found a recipe I could use. Try, try, again! Mixing it can be hard, but if you keep trying you will get there.

8. It can be colored with almost anything

Pastels mixed in clay, acrylics mixed in clay, pastels 'painted' on clay, acrylics painted on clay, and oil paints. Many mediums can be used to color air dry clay.

9. Polymer clay tutorials can be modified for air dry clay

If you can't figure out how to make something and you look up a tutorial, almost everything is going to be polymer clay in the US. Don't worry; you can modify those tutorials for air dry clay. The main difference is going to be that polymer clay is stiffer than air dry clay and needs to be baked.

10. Homemade clay actually lasts longer than most people say

A lot of people on the internet who have tried cold porcelain clay will tell you "Lasts about a week". That isn't true. It will last a lot longer than a week as long as you wrap it in plastic wrap and store it in an air tight container when not in use. Mine generally lasts around four to five months, and that is because by four or five months after making it I have used it all.

Good luck in your clay endeavors. It is definitely worthwhile, and I hope you enjoyed this tutorial!

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