Silicone mould making is one of those skills that opens a door to endless creativity. Once you learn how to make your own moulds, you are no longer limited to what you can buy in a shop. You can capture textures, shapes, and small details from almost anything around you. From jewellery and figurines to functional pieces like coasters or keycaps, silicone moulds enable the reproduction of consistent results while maintaining the freedom to experiment.
This tutorial guides you through the entire process from selecting materials to creating, curing, and caring for your moulds. It focuses on RTV (room temperature vulcanising) silicone which is the most common type used by artists and makers. The goal is to help you understand why each step matters not just what to do.
### Understanding Silicone
Silicone rubber is a flexible, durable, and heat-resistant material. When it cures, it becomes elastic yet stable, which means it can withstand repeated use with resins, plaster, wax, and even low-temperature metals. It is also self-releasing so the resin does not stick to it once it is cured. That combination of strength and flexibility is what makes silicone ideal for mould making.
There are two main types of RTV silicone: tin-cure and platinum-cure.
**Tin-cure silicone** (condensation-cure) is the most forgiving for beginners. It is cheaper and works well with most resins. The downside is that it can shrink slightly as it cures and does not last as long as platinum-cure.
**Platinum-cure silicone** (addition-cure) is more precise with very low shrinkage and high tear strength. It also lasts longer but costs more and is sensitive to contamination. Sulphur, certain pigments, and some types of modelling clay can stop it from curing properly.
For most craft and resin projects, tin-cure silicone is perfectly fine. Once you have more experience or require higher detail and longevity, consider upgrading to platinum-cure.
### Tools and Materials
Before starting, gather all the necessary materials. Once the silicone is mixed, you are on a tight schedule, so thorough preparation makes a big difference.
**You will need:**
- RTV silicone rubber (tin or platinum cure)
- Silicone catalyst or hardener (if not pre-mixed)
- Mixing cups (plastic or silicone)
- Wooden or silicone stirring sticks
- Digital scales for accurate measurement
- Mould box or container
- Glue gun or modelling clay for sealing
- Release agent (optional)
- The master object (the item you are moulding)
- Nitrile gloves and protective surface covering
Having everything laid out before mixing helps avoid mistakes. Silicone does not wait for you to find a tool once the reaction begins.
### Choosing a Mould Box
A mould box is the container that holds your master and the liquid silicone while it cures. You can buy commercial mould boxes but most makers build their own using simple materials.
Common options include:
- **Plastic food containers:** Cheap, reusable, and come in various sizes.
- **Acrylic or foam board:** Cut panels and glue them together with hot glue.
- **Lego bricks:** A favourite for small moulds because you can build to size and reuse them.
Whatever you use, make sure it has smooth walls and a tight seal to prevent leaks. You can apply a thin layer of petroleum jelly or hot glue along the edges for extra security.
### Preparing the Master Object
The master is the original piece you are replicating. It can be made of almost anything, wood, metal, plastic, polymer, clay, or an existing resin cast. Clean it thoroughly to remove dust, oil, or fingerprints. If it is porous, seal it with a thin layer of varnish, PVA, or clear resin. Otherwise, air trapped in tiny pores can release later as bubbles.
If your object has undercuts (deep grooves or shapes that hook inward) consider making a two-part mould. A single pour mould might tear when you try to remove it.
### Measuring and Mixing Silicone
Accuracy is crucial here. Check your silicone packaging for the correct mix ratio. Some are 1:1 by volume, while others use 10:1 by weight. Always adhere to the manufacturer's instructions.
Pour both parts into a clean mixing cup. Stir slowly, scraping the sides and bottom to blend thoroughly without incorporating air. A slow, deliberate stir is better than a quick one filled with bubbles.
If you have access to a vacuum chamber, degas the mixture for about a minute. This removes trapped air, leading to a smoother final mould. If a vacuum chamber isn’t available, tapping the cup on the table or letting it sit for a few minutes can still help bubbles to rise.
### Pouring the Silicone
Pour slowly from a height of about 12 to 18 inches in a thin, steady stream. This helps break surface tension and allows bubbles to escape as the silicone flows into the mould box.
Start pouring at one corner rather than directly on top of the object. Let the silicone naturally flow around it. This reduces the chance of trapping air against the surface. Continue until the object is covered by at least 10 to 15 millimetres of silicone.
If your master has fine detail, gently tap the mould box or vibrate the table to help bubbles escape.
### Curing
Leave the mould to cure undisturbed at room temperature. Most silicones set in 4 to 24 hours, depending on the brand and mix ratio. Cooler environments slow curing while warmer ones speed it up. Avoid moving the mould during this stage; vibrations can cause surface ripples.
Do not try to speed up the process with direct heat unless the manufacturer specifically allows it. Too much heat can cause the silicone to cure unevenly or even warp.
Once fully cured, the silicone will feel rubbery and flexible, not sticky or soft. If any spots remain tacky, the mix ratio might have been off, or contamination may have occurred.
### Demoulding
Carefully pull the mould away from the box. Gently flex the sides to release the seal, then peel the mould back from the master. If you used a release agent, it should come away easily.
Take your time here. If the silicone sticks or stretches, it might still be slightly uncured inside. Let it sit for a few more hours before trying again.
Inspect the mould. Look for air bubbles on the surface, thin areas, or tears. These clues help you improve next time. Small surface bubbles are normal and often do not affect the cast.
### Two-Part Moulds
When your object has details on both sides or deep undercuts, a two-part mould is necessary. The concept is simple but requires patience.
1. Build a mould box that fits your object with a few centimetres of space around it.
2. Embed half of the object in clay, leaving the other half exposed. Smooth the clay surface.
3. Create small registration keys (tiny round holes) in the clay using a pencil or ball tool. These ensure both halves align perfectly.
4. Pour the first half of the silicone and let it cure completely.
5. Once cured, remove the clay, leaving the object in place.
6. Apply a thin coat of release agent over the cured silicone surface to prevent bonding.
7. Pour the second half of the silicone over it.
8. Once cured, separate the halves and remove the object.
The result is a precise, two-part mould that can be easily opened and closed for multiple castings.
### Using the Mould
Before casting resin, ensure your new mould is fully cured and clean. If there is any residue or dust, rinse with mild soap and allow it to dry completely.
Pour resin slowly into the mould to prevent bubbles. Some makers use a light mist of alcohol or spray mould release to help the resin settle. Once the resin has cured, demold carefully by flexing the sides. With experience, you will learn how much pressure each mould can tolerate.
### Caring for Silicone Moulds
A good mould can last dozens or even hundreds of uses if properly cared for. Always keep moulds clean and out of direct sunlight. UV light gradually damages silicone, leading to yellowing or becoming brittle.
After each use:
- Wash with mild soap and water.
- Allow to air dry completely before storing.
- Lightly dust with cornstarch to prevent sticking.
- Store flat in a cool, dark place.
Avoid using sharp tools when removing resin pieces. Apply gentle pressure instead of pulling or twisting.
If you notice small tears, repair them with a small amount of uncured silicone applied like glue. Let it fully cure before reuse.
### Troubleshooting Common Problems
**Bubbles trapped in detail areas**
Mix slowly and pour in a thin stream. You can also brush a small layer of silicone over the surface before pouring the rest.
**Mould did not cure**
Check your mix ratio and ensure the components are compatible. Some clays or 3D printed materials contain sulphur or residues that hinder curing. Use a sealant or release layer next time.
**Surface feels sticky**
The environment might have been too cold or the silicone was undermixed. Allow more time or double-check your ratios.
**Tearing during demoulding**
Use a thicker wall next time or select a silicone with higher tear strength. Always demould gently.
**Deformation**
Ensure the mould box walls are rigid and well-supported during curing. Flexible boxes can bow under the weight of the silicone.
### Why Make Your Own Moulds
Creating silicone moulds is both practical and creative. You can capture natural textures from leaves, shells, or fabrics, or replicate your sculpted designs exactly as you envisioned them. It enables you to scale your projects, combine different materials, and experiment with various casting media.
The first few moulds might not be perfect, but each one teaches you something. Once you understand how silicone behaves, you'll start to see the world as full of potential moulds waiting to be created. That is the true joy of it. You are not just copying objects; you are learning to preserve form and detail in a flexible, reusable way.
### Final Thoughts
Silicone mould making is a craft that strikes a balance between precision and intuition. The materials are simple, but small details such as mixing speed, temperature, and pouring direction make a significant difference. With time and practice, you will be able to produce moulds that look professional and last for many years.
It is worth keeping notes on every pour, including the type of silicone used, the ratio, the room temperature, and the time it took to cure. These records will help you improve your process. Soon you will start designing objects specifically for moulding, planning how silicone will flow and release before you even begin.
There is something satisfying about holding a perfect cast from a mould you created yourself. It is the moment where technique meets creativity and that blend is precisely what makes resin and silicone such rewarding materials to work with.
