Gemstone Sculptures : How to Sculpt Minerals & Crystals from Polymer Clay | Stephanie Kilgast | Skillshare

Gemstone Sculptures : How to Sculpt Minerals & Crystals from Polymer Clay

Stephanie Kilgast, Contemporary artist.

Gemstone Sculptures : How to Sculpt Minerals & Crystals from Polymer Clay

Stephanie Kilgast, Contemporary artist.

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8 Lessons (40m)
    • 1. 1. Introduction

    • 2. 2. Materials

    • 3. 3.1. Sculpting : Rhodochrosite

    • 4. 3.2. Sculpting : Rhodochrosite with Quartz

    • 5. 3.3. Sculpting : Vanadinite

    • 6. 3.4. Sculpting : Chrysocolla (normally pale blue)

    • 7. 3.5. Sculpting : Agate Slice

    • 8. 4. Final Words

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About This Class

An extensive class to go into depth on how to mix colors, what materials to use, which sculpting tools to use to sculpt just any mineral you would like.


During this class I am showing how to make five different minerals from scratch with my own color twist inspired from real minerals.
For inspiration, I invite you to check out my pinterest board :


The class is organized like follow :

1. Introduction
2. Materials
3.1. Sculpting : Rhodochrosite
3.2. Sculpting :  Rhodochrosite with Quartz
3.3. Sculpting : Varadinite
3.4. Sculpting : Chrysocolla (normally pale blue)
3.5. Sculpting : Agate Slice
4. Final Words

Meet Your Teacher

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Stephanie Kilgast

Contemporary artist.


Inspired by natural forms, Stéphanie Kilgast’s artwork is an ode to nature and its current biodiversity. Plants, mushrooms, insects and other animals encounter in a vibrant swirl of colors under her brush or sculpting tools.

Since 2017, in her series “Discarded Objects”, she grows colorful organic sculptures on human-made objects, celebrating the beauty of nature in a dialogue with humanity, questioning the lost balance between human activities and nature.
Her work has a cheerful post apocalyptic feel to it, a reassuring reminder that nature has the capacity to grow back, if we only let it.

She built her reputation and her sculpting skills around hyperrealistic miniature food sculptures. Her wo... See full profile

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1. 1. Introduction: Hello. I am Stephanie, I'm an artist and welcome in my interview. I'm going to share with you all I know about sculpting crystals and gemstones. I finished sculpting a lot of them for my sculptural paintings and they are very fun project to do. This is an extensive class and I'm going to share five different crystals and how to sculpt them. 2. 2. Materials: For this class, we are going to need quite a few materials. The most important is the polymer clay. I am going to use Cernit translucent, however, you can use Fimo or Pardo translucent. Those three brands are the only one I really recommend because you are going to have a very beautiful translucency. Also am going to use the Cernit translucent in yellow and in red ruby, although it's more of a pinkish color than red. For other color mixes, I am using acrylic paint, but you can also use oil paints or alcohol inks. We're also going to use some silver and golden foil. I use this one from Fimo, but there are other brands that do it. We're also going to need some white acrylic paint to highlight details, any white acrylic paint will do. This is the study. Acrylic paint, which is perfectly fine, however, for the color mixes, I recommend to take some fine acrylic paint simply because the pigments are going to be a lot better. We are also going to need some varnish at the end, so I use the Vernis Glassificateur from Cleopatre. I cannot really recommend any good varnish outside of France, so maybe ask your local craft store what is best varnish to use for polymer clay. As for the tools, I am going to use some blade, if you are going to need a long blade, an exact knife is optional but always nice and some razor blades with some tape, but you're also going to need a toothbrush or some sandpaper, a silicone tool or shaper, needle tool, a ball and the tool or a few different ones. Those two tools which are spatula tools, these are handmade tools that you can only buy from AMCreatures on Etsy. These other tools you can find in any online or local craft store. A toothbrush, you can find at a glossary store. 3. 3.1. Sculpting : Rhodochrosite: I'm going to show you how to sculpt rhodochrosite or something that looks similar to it. For that I used a base of translucent clay, I used Cernit, but Fimo, or Pardo clay will work just as fine. What I did is to cut three pieces of translucent clay. Then I'm going to condition them, which means simply mixing them and softening them through a pasta maker, but you can do that with your hands as well. Then I'm using two different acrylic paints. The first one is Medium Magenta from Golden, and the other one is Chinacridon Magenta from PRIMAcryl. But any fine acrylic paint will do. As you see, it's getting a bit messy, but I'm mixing the acrylic paint with the translucent clay. I'm mixing paint with clay to keep a high translucency in the clay. As you see, I'm mixing a lot with my fingers and not through a pasta maker simply because if you don't mix it thoroughly before using a pasta maker, you are going to make a huge mess of your pasta maker, and you might end up having paint into your pasta maker and ruining it. So using your hands is the best way. I also made a mix using translucent clay and translucent colored clay. I've used Ruby-Red from Cernit Translucent Clay. The with the three colors I had, I transformed them into five in order to get a gradient from the strongest colors to the lightest one. As you can see, I simply divide the colors I have and then roughly mix them together, and then I have a nice gradient of five colors. I really hope the pictures are a little bit more clear because it's hard to explain. What I did next was to add some gold foil between the layers. It's a golden foil that I got from Fimo, I think, but there are many different brands who do that. Then I simply stuck all three sheets on top of another, and then, again, I roughly mix everything together. Since the rhodochrosite doesn't show any gradual gradient, but different colors always make it more realistic, that's why I did that that way. The reference picture I had and how I wanted it to be was to have a dark base. I'm not sure exactly what kind of rock it is, but I simply mixed black, gray, and a mix of ocher and white. All of these are half translucent, half color, simply because I think when you mix half translucent in any kind of color, it makes your end product a lot more realistic. As you saw, I added some golden leaf between the layers and I roughly mixed them by putting them together through a pasta maker. Here I just roughly shaped the base, and now I'm using a blade, basically, real razor blade that you can find in stores. I really like to use these because they are very cheap and they are very thin, so they make very clean cut. However, they are also very sharp. Hence why I added the tape on the other side so I would not cut myself. Now, I am cutting the crystals into crystal shapes. You want to have a base shape that is rectangular, and then cut a pointy end. Then you put everything together. I also added some liquid clay between the black base and the rhodochrosite crystals. This is to ensure that everything sticks nicely together so it forms a very strong bond because it's polymer clay. It's like soldiering both polymer clays. I do that because I don't push the crystals very much into the clay, so I really need that bond. You cannot really push the crystals in them without altering their shape and you want the crystals to be very straight. That's why I do it that way. You have to keep in mind that you need very sharp edges for the project, otherwise your crystals are not going to be pointy. If they're not pointy, they're not going to look like crystals, so this is really important. One thing that might happen is that your clay is too soft. If your clay is too soft, you have a few options. You can put your clay into the freezer for not too long, maybe half an hour in the fridge. I never really tried with a freezer what I would just say, 10-15 minutes. Or if it's not too hot where you live, you just leave it aside and wait for it to harden a bit. Usually, when you work with polymer clay, and you have it in your hands, it tends to warm up the clay, especially when mixing. Often, just waiting one hour for it to cool down a bit is sufficient to have a more resilient clay, and so you don't smoosh everything together. I think that's not a step that you should take lightly, especially if you want some straight edges. I did cut out a few thinner crystals just to make it more realistic. You don't want them all to be the same size. I showed you reference pictures in the beginning. Now's a good time to have it on hand to really look at it. Also add a few bits of red clay around just to add some more realism. Here I'm working the base. What I'm doing is tearing apart the polymer clay. I'm using here spatula tool, which I really like, but honestly, a toothpick would work as well. As you can see, I'm just tearing everything apart because I have realized when you tear polymer clay apart, it looks like rock, especially if it's not well mixed. This is a very good technique. Here, I'm using a needle-ended tool to just add a little bit more texture. Again, a reference pictures is really helpful in that case, so you can really replicate what you are seeing in sculpting. With all sculptures, I would always recommend to take your time to get it perfect. Usually, you're not in a rush. I would say with art in general, it's better not to rush. Sometimes, it's nice to have something done quickly, but you'll be so much more happy if you took one-half an hour more just to make it look right instead of rushing it and being a bit sad when it's not quite as perfect. Then I baked it. Try to note I'm baking, I tend to bake at around 120 degrees Celsius and for 40 minutes. You can bake as many times as you want the polymer clay, but just be sure that the last time is rather long. That's why I do it 40 minutes. It can be actually longer. The thing is, with polymer clay, sometimes people are afraid to overbake it, but really underbaking is the problem. If you underbake your clay, it can crumble and just not hold it together. Overbaking world just alter the color a bit, but that most of the time can be fixed. Yeah, rather be afraid of underbaking than overbaking. After baking, just to have those nice edges, I'm adding some white acrylic paint on all edges. It doesn't look sharper, but you actually can see the edges a lot more. With crystals, you don't have that problem simply because crystals are lot more translucent and the edges are really sharp. The edges are actually thinner, which makes the light reflect on them a lot better, which isn't the case with polymer clay. It's cheating in a way, but this is how you make your edges look really sharp. Simply dip your brush into acrylic paint. You don't want to put too much on it. In case you put too much on it, it's not too much of a problem either. You can always scratch your baked surface off with a knife or a blade if you put too much acrylic on it, so that's not something to be too worried about it. Just be sure not to miss any spots. You also want to brush some white acrylic paint on the black base. Eventually, you are going to glaze all the crystals, and you're done with the replica of the rhodochrosite. 4. 3.2. Sculpting : Rhodochrosite with Quartz: Now, I am sculpting another rhodocrosite, but on quartz, and for that one I used only one color, I used the translucent clay as usual, and I used medium magenta again from golden and mixed it together by hand simply because it is less messier, or it's not less messier, but it's not going to mess up your pasta maker. Once it was nicely mixed, I shaped it and flattened it, because this time it's going to need to be cut into squares, and for the base I used a mix of various scraps of clay, dark and ocher and black, and also some white with some silver foil, some translucent white with some silver foil that I made for another crystals previously, not in this video but before. Now I am cutting squares out of the pink clay. As you can see on my reference pictures, it's very cubic. I decided to make the squares a little bit smaller or thinner, and I'm simply putting them on that black base. You want to have a firm clay, so if it's not firm enough, let it cool down for a while before cutting it and use a blade that is very sharp. I really like to use those razor blades. Now what I did is, I did have a leftover mix of translucent clay with some silver foil, and I'm using that to add on the black base, and I'm also using a simple translucent clay to make more crystals, the quartz crystals, I guess, to put all around simply because I really liked that reference picture and I wanted to be rather close to that one. For the small crystals, I start to cut very thin stripes and then I make the end of them pointy. I basically cut out a V-shape and then turn it and another V-shape, just a V-shaped if it's really thin. I also added some quartz, some white crystals on top of the pink one. Because it really looks nice when you have crystals on crystals. However, be careful not to squish the first crystals with the segment when you put it on. I'm adding more clay. I thought the clay was too dark. So I did another mix of black and white to have something that is more grayish, and here I'm just continuing to add a few pink squares and more of the gray clay, the gray mix around and crystals. I think with any sculpture and I know I tend to repeat myself, but it's really important to take your time and to use reference pictures, it's always best to have more than one and to try to replicate what makes it look real. In that case, often with crystals is to add many different sizes of crystals, bigger ones and very small ones and to add them in a very random way, and to play with textures a lot, so the crystals themselves are very simple and clean cut. But some, the base often is a bit rough and very textured. So it's this opposition in crystals that makes them look real as the position between the clean cut and the rough texture that usually makes things look real. Yeah, I'm just stressing a bit that the pink rhodocrosite with a blade and just adding a bit more texture all around. I didn't go too much into details about the mix of the black one simply because I usually tend to go with scraps I have at home. If you look at rocks often, it's a mixture of black and brown and ocher and white, and I think that's really what works best is to work with scraps and then just go from there. After baking, I added some white acrylic paint on all the edges to make them stand out more, and roughly also painted the base with some white to show the texture off a bit. Simply put, the acrylic paint is to highlight the details. After letting everything dry, I coated it in vanish and well, this is it for the rhodocrosite with quartz. 5. 3.3. Sculpting : Vanadinite: Now the next crystal we are making is very [inaudible]. And for that I used translucent it in white, in translucent and a bit of yellow, which I mix together. Then I added some acrylic paints, camine, and then I mix both together. It's best to mix lease between your fingers because then you are going to have messy fingers, but not a messy pasta maker. As you can easily wash your hands, but Pasta making or too much. This time I did a very rough mixing. So as I don't have to make different mixes and I already have a lot of interesting shapes in it. Then I added some golden foil. The foil I used is from female, but there are many others. Then I simply stacked sheets of clay and mixed again in a very rough way and then formed of rectangle or brick. It's actually more of a brick. Now to make vanadinite, you are going to cut out hexagons, and for that, you have to keep in mind that hexagons have six sides and they are parallel, two-by-two. I start out with two parallel lines, and then at one side I make a V shape. And then I make the other sides parallel to the two other ones. You also have to keep in mind that all sides are actually the same size. And if you mess up like eyelid here, you just pushed together and then cut a bit of the excess. It's a little tricky to do, but it's not too difficult and you can always cut again to get the exact shape. Also, don't worry if it's not perfect. You just have to recognize an hexagon. Now here again, as I said, two parallels than to V-shapes and try to have all sides of the same size. C parallel, same side. Put together if it's not perfect. Now for the base, so I mix black, white and a very light or cool or champagne together. My technique usually is to put all the colors I want to mix together. If want a rough mix and then cuts them in a veryy rough way and stack them again. This is working great for rocks where you can have two very different colors next to each other and still have kind of makes. Then I mix it very roughly between my hands, and it goes through a pasta maker. After that, I roughly shape the base. It needs to be quite irregular. I add some silver leaf on top of it. I added last this time because I want quite a lot of silver leaf on the outside and interests roughly mixed it in. Now I'm preparing spots to add the very dinettes the orange crystals while also starting to texture the base. In a way you are making indents to add the hexagonal shaped crystals and then add them to the base. You want to add all sizes of crystals, so also aren't very tiny ones. I work on the bass and on the tiny chunks of the colored clay, and also, while also texturing the dark base that is almost black. Here again, I am texturing everything was my spatula tool and also tearing apart the clay to get that rock texture that is so crucial for a mineral or gemstone. It's really about trying to add more and more details. I don't think you can really go overboard when replicating and mineral as reality is full of details. It often is what makes the difference between a good sculpt and gioco sculpt. Then bake, after baking, use some white acrylic paint to highlight all the edges and details and textures. White paint really is what is going to make your sculpture pop. I think it's quite visible. Also, when you are making translucent sculptures, you are going to realize that the color is darkening after baking that is because the translucency actually comes out only when baking and before it's. Your colors, your mixes are always going to look a little bit pastel before baking and a lot stronger after baking. Then ironist the crystal part, not the black one. That's pretty much it. 6. 3.4. Sculpting : Chrysocolla (normally pale blue): For this one, I was inspired by the mineral chrysocolla. As you can see, it's normally blue, but I wanted it in pink. I went with pink. For that pink shade, I simply used the same pink shade I used for the rhodochrosite with quartz. It's translucent clay with a bit of medium magenta acrylic paints. For this one, I started to roughly sculpt a base on top of which I am making tiny balls of clay. Now I knew I wanted to use this mineral with a flat back so I could integrate it in one of my sculpture artworks. However, if you want to be able to hold it in your hands then you probably need to make the back after. Which I don't do and which I'm not sharing. It's not impossible to do. It's not really difficult either. It starts pretty much the same as now. I am simply adding many, many tiny balls everywhere. Well, just looking at the reference picture and trying to make it high and low and to have some interesting indent silverware. After that, I used a silicone tool to smooth everything so you don't really see the edges like we still do now. You could use a toothpick for that. However, this time, a silicone tool really works much better. Because the silicon tool, sometimes it's also called a clay shaper, really helps to smooth everything out. You can find it in any local craft store. After that, I textured with a toothbrush first. I simply pushed everywhere. You can use sand paper as well. However, since it's very sculpted and there are a lot of up and downs, a toothbrush is a lot easier to handle than actual sandpaper. I used a needle ended tool, to add some more texture everywhere. Alternatively, you can use a needle or a toothpick. You want to make sure that you have tiny holes everywhere, and that it must start to look like a rock. I'm only going to texture the tiny balls, the pink balls and not the still flatten things because I'm going to cover them afterwards. Now I'm adding some liquid polymer clay on top of all of the textured balls, and I'm going to put some glitter on top of it. I just add quite a lot. The liquid clay is going to be the glue that glues the glitter to the pink clay. Then I bake, and after baking, I'm using a brush I really don't care for, and I am removing the glitter that is too much. Now glitter is pretty tricky to work with because it tends to go everywhere. So really be careful to remove all the excess glitter and to throw it away. Try to keep everything clean, otherwise you are going to end up with glitter on all your other sculptures and you don't really want that. After that, I prepared the rock part. As you can see, I have a lot of scrap clay from the previous minerals and crystals I made. I'm just adding some more och-re and black and brown and all kinds of odd colors. Making a rock is always quite interesting because you have to analyze what colors can be in the reference picture and then you kind of mix everything in a rather random way. Then I put it through the pasta maker and then I started to cover everything. I'll just cut out a few chunks of clay and then put it around. Now you might notice that I didn't use liquid clay. It is because I push it enough into the baked clay, the raw clay into the baked clay. It's going to stick enough. You can of course brush it first with some liquid clay just to be sure. But usually, if your raw clay is soft enough and you push it strongly enough and on a big enough surface, it's going to be just fine. I thought the the rock was a bit too dark, so I added to the mix a little bit of that white in ocher color just to lighten everything up. This is really where you have to trust your eye and your reference picture to help you out and see if it's enough or not. Then you start to texture everything. I really like to use my spatula tools for that and scratch the surface, remove some bits, use toothbrush, maybe sandpaper. Really, it's about using all the tools you have to try to find which one works best. I don't think there is an ideal tool for that. It really is about adding as much texture as you can. Yeah, I'm just putting the reference picture I was using for that. I'm adding some of that pink crystal pink clay on the edges between the rock and the minerals in the middle. I'm just going to put them all around to have a transition between the pink and rock. I'm adding some of the och-re thumb of the white och-re makes all around us well, just really sticking to the reference picture. Sometimes it's good not to overthink this and look at what you like on your reference picture and then just go for it and replicate that. This is also why it's so important to use reference pictures because unless you've been sculpting certain specific thing for years. Usually you have a very abstract idea of what rock or mineral is. This is where reference pictures really help to bring your sculpture to the next level. Again, here adding a little bit more texture all around the rock with various tools. Then you bake everything a second time. After baking, I added some paint. I did a mix of white and ocher, and I brushed it all around on the rocky part of the mineral. Then I also varnished the pink and that's pretty much it for that one. 7. 3.5. Sculpting : Agate Slice: For the agate slice, it's great to do this as a last project, simply because I am going to use a lot of scrap clay from all the crystals I have previously done and maybe add in some other mixes. You want a fair mix of translucence clay and also opaque clay. Here I am using, as I said, left overs of crystals, but also some yellow, orange, and white which are going to be opaque. Knowing that they're always in all my opaque mix I use half of translucent in them. Then you simply roll them all out through a pasta maker to make thin sheets. Then you are going to stack them. This is the reference picture I used. I didn't do it exactly like that, but I was going for orange, pink color theme, and so it was kind of accurate. As you see now, I am simply stacking different kind of translucent and opaque colors. As the rule I would say white really helps to make the colors pop, so try to alternate a darker color with a lighter one and white in between. Also try to alternate opaque and translucent and sometimes double the color as sometimes the layers are a little bit thicker. But honestly it's mostly, you're going to have to trust your eye on that one and try to find what you like best. There are many agate slices you can find on Pinterest. Don't be shy and see those there will really help you if you need some inspiration. I wasn't too close to my reference picture, so the one I showed previously, but it did help quite a lot to figure out the colors and the layers et cetera. Now for the next step, you're going to need a very sharp blade, and you need a very sharp long blades. Typically, polymer clay blades you can buy in a sharpener crafts store et cetera. Here I made a first cut. You want a very clean slice of those stripy layers, and I worked around a center that I used. I used an orange with golden leaves center. Here I'm trying to replicate the shape of an agate slice using the reference picture I showed. Then just cut and make sure the layers actually fit together, which I am doing here. You can simply brush one clay to the other one just to make sure it looks nice. Then add indents all around to make it look like it's been a rock outside. As you may or not know, an agate slice, is slice of a rock. So the outer edge is supposed to look like a rock with indents and textured and et cetera. This is what I'm doing here. Now I ended up adding another layer of a whites and translucent mix. I actually used the porcelain white from Sonnet, which is already a mix of half translucent, half white. Now this is because I wasn't quite happy with my agate slice and I thought some white around would just make it look neater. However, if you plan a little bit ahead, you can put that in your layers in the first step and then slice it which will make everything a lot easier than what I did. Now I'm mixing a bunch of scrap clay. What I usually do with rock is a mix of dark. Darker shades, black, brown and lighter like white and aqua, and I just cut out stripe, a thin strip and I'm putting it all around. Then I'm going to texture it. I use various tools and I ended up using a ball and a tool and my spatula tool the most. You just want to be sure that the outside looks like rock. It really needs to be rough. You could also use a toothpick instead of those fancy tools that works as well. Toothpicks are great tools to sculpt, and they're really cheap, so don't be shy to use toothpicks. Then I simply flattened the agate slices between two tiles. Just be sure you don't squish one side more than the other, and then bake. After baking, I removed it carefully with blade and then I painted white all around. I did not vanish it because you simply don't need it because the way you bake it on the tile is enough to make it look shiny. 8. 4. Final Words: This is all I have learned sculpting crystals and minerals over the years but now it is your turn to do something. Pick a crystal you like, pick a color you want, and then make your own crystal. I really look forward to seeing your projects and if you have any questions about the tools or certain techniques or maybe something you didn't quite understand, just ask me. I am here to answer all the questions. Thank you so much for watching and I really hope to see you in my next video. Bye.