Making Your First Silicone Mold? Learn From My Mistakes.
Updated: Jul 28
So I had this 3-year-old unopened box of Mold Star 20T silicone mix. I had planned to use it someday for fun, but just never got around to it.
I thought making my first silicone mold would be simple: build a mold box, mix the silicone, pour, and wait. Instead, I found myself questioning almost every step and learning several lessons the hard way. If you're about to make your first silicone mold, I hope these mistakes save you time, money, and frustration.
So my first thought was "I have these beautiful ceramic vintage angels on my refrigerator. They would make some great molds to make more beautiful angels from. They're flat on the back, so these should be perfect."
💡LESSON #1: Don't start with something valuable or sentimental. You'll find out why soon.
Then I needed something to hold the silicone that would fit the angels well. I went to the dollar store and figured I could find something inexpensive. "Too big, too small", nothing fit. And then I found it!...3 glass bowls with lids, one for each angel, made of glass, inexpensive. "Glass is slippery, right? The molds should slip right out. I'll use a bit of rubbing alcohol to help the mold slip out. This should work." I took it home and was so excited to start my project.
💡LESSON #2: Don't use rigid containers such as glass because it doesn't flex. That decision came back to haunt me.
Then I realized the magnet on the back of the angel caused the angel to be slightly elevated off the bottom of the bowl. "This is a 30 year old angel. If I try to pry off the magnet, it will probably break the angel. Ok, we better leave the magnets alone."
💡LESSON #3: Always make sure your entire object is flat on the bottom.
We'll come back to this.
I tested the bowls by setting the angels inside, face up, and they fit, but there was only a tiny bit of space between the angel and the bowl. So if the angel were to shift at all while pouring the silicone, it would be pressed against the glass.
💡LESSON #4: Make sure the container for your mold has at least a 1/2 inch gap between your object and the edge of the container.
"Hmmm, this one keeps moving. If I just set it here and pour the silicone, the angel may move and touch the glass. I have a fix for that. I'll use a tiny bit of double-stick tape."
💡LESSON #5: Don't use double stick tape to mount your object. It seemed like a great idea...at first.
"Ok my molds are ready for pouring. Lets read this box and see the directions. Ok mix equal parts A and B. Stir Parts A and B inside the bottle before using. Easy." Surprisingly, mixing the silicone turned out to be the easiest part. I stirred Parts A and B separately in their bottles before measuring them.
Well...this silicone package was several years old. But even so, there were only a few areas that had thickened up, and I was able to loosen and stir it for the most part.
"Ok, let's mix this stuff". So, just like with epoxy resin, I placed part A in one cup, part B in another cup, then poured them both into a 3rd empty cup, stirred slowly, it mixed perfectly and I was pleasantly surprised that it was clear, not purple like the picture on the box. "That means I can use this for my resin projects too - cool!"
I slowly poured the silicone into the container to the side of the angel and let it spread across the container until the angel was covered. This helps trapped air bubbles rise to the surface as the silicone fills the mold box.
"Doggone it - I should have made more silicone. Now I have to make more for the other two angels". And by then I was near the end of the mix, so I just mixed up the rest and poured one more blank mold. I had some metal earring shapes that were intended to make clay earrings from, but they were perfect to make my own molds out of.
So I waited a few minutes until the silicone had slightly began to thicken, and then carefully set them face down on top of the silicone, and gently pressed them down until they were level with the silicone. Now I had ANOTHER unexpected mold, and I was excited to see how they would come out.
💡LESSON #6: If you know how much silicone you will need, it's better to "Mix once, Pour once". I ended up having to make 3 batches.
Once all 3 angels were covered I let the silicone cure. It will be cured when you can press the mold with a fingernail and it doesn't leave a mark.
"Now comes the fun part. Time to de-mold." This is where all my mistakes hit me at once....
First of all the glass did not slide at all. I poured in a little rubbing alcohol around the edge, and it did help separate the silicone from the sides of the glass bowl. BUT I couldn't get the mold to move at all. It wouldn't twist. And the glass does not flex.
I used a tool but couldn't get it deep enough to get under the mold. I asked hubby to help - always a great backup. But nothing moved. I'm pretty sure it was because of the double stick tape.
And you know that trick with pricing labels when they don't wanna come off, and you can apply heat and it will loosen the glue so the labels peel off easily? Well, I even tried that. Nothing.
I was bound and determined to get this mold out of there. Eventually I gave up, and just decided to try to get the angels back out and forgo the whole silicone process. So....I placed the bowl in a Ziploc bag, and smashed it with a hammer!
The glass broke, and although I could physically reach the mold now, there was also glass splinters all over it. I figured "If I'm careful, and I wear the rubber gloves I should be able to get it out".
💡LESSON #7: Rubber gloves are NOT cut-resistant. Don't do it. No project is worth a trip to the emergency room.
So I took a razor knife and figured "I can cut the mold behind the angel and pull it out thru a hole". After the first poke of glass, I gave up on the whole project. My health is more important than this project.
Unfortunately it was a big loss.
💸 I lost the cost of the silicone package (about $42)
🥣 and the glass bowls (about $6),
❤️ and worse thing was I lost my beautiful angels that I've had for over 30 years (sentimental, and irreplaceable).
✅ So in summary:
For your first project do not use an object that is sentimental or valuable because you're still learning, and if something happens, you may lose that object altogether like I did.
For the container, do not use glass. You can use something plastic and flexible such as Deli containers, Soup containers, Yogurt tubs, Cottage cheese containers, Margarine tub, disposable plastic cups, small food storage containers with smooth sides.
Always make sure your object lays flat on the bottom of the container. If you need to fill gaps or support your original, a soft, non-hardening modeling clay (plasticine/plastalina) is the easiest choice, although polymer clay will also work if you already have it.
Make sure the container for your mold has at least a 1/2 inch gap between your object and the edge of the container. If the object is too small, the object will press against the side of the container and will leave an empty edge of the side once removed. In reverse of that, if the container is too big you'll be wasting more silicone than needed, and that stuff is expensive.
Don't use double stick tape to mount your object. If you need to keep it in place, you can use a small amount of Museum putty or Museum Wax.
If you know how much silicone you will need, it's better to "Mix once, Pour once" - in other words, try to mix it all in one go if possible. And, it's always a good idea to have an extra container nearby in case you need to use up the tail end of your silicone.
If you are working with broken glass, do not use rubber gloves - they won't protect you from the glass. It's better to wear leather work gloves or cut-resistant gloves.
⚠️ Safety Note: Breaking glass creates razor-sharp shards. If you ever find yourself in this situation, stop and reconsider. No project is worth an injury.
Although this project was a disaster, I did come away with a lot more knowledge. Would I do it again? Absolutely, but applying the lessons I've learned to it. In fact, now that I've made my first molds, I'm looking forward to making my second set. My next mold won't be perfect either, but it'll already be miles ahead of my first.
Just a note: in case you're wondering what silicone product I was using, I used the Smooth-On Mold Star™ 20T. The texture turned out like soft rubber. Flexible, but tough. I think next time I might use the 30T instead to be just a little less wiggly. But considering it was 3 years old, I was happily surprised at the final results. The silicone worked perfectly. And my earring mold came out beautiful.
So...in closing, I hope you can learn from my mistakes. And I wish you the best of luck on your silicone mold-making adventure.
Until next time... happy creating!