Replicating Polymer Clay Miniatures: Making 3D Two-Part Silicone Moulds

Making detailed polymer clay figurines and charms by hand takes a lot of time and practice. If you want to make several copies of your favourite clay piece, making a 3D two-part silicone mould is the best way to do it.

This guide explains an easy, step-by-step technique to clone your 3D clay creations using liquid resin. You will learn how to make alignment locks (keys), add release cuts, and hold the mould together with rubber bands.

Materials & Tools You Need

• Your Finished Sculpture: A fully baked, clean polymer clay figure or charm.

• Liquid Silicone Rubber: Standard silicone moulding rubber (soft and stretchy silicone works best).

• Mould Box: A simple small plastic container or Lego frame (about 1/2 inch larger than your figure on all sides).

• Sulfur-Free Oil Clay: Non-drying clay (like Monster Clay) to build the base. Note: Avoid regular plasticine that has sulfur, as it stops silicone from curing.

• Alignment Tools: A few small marbles or the round end of a paintbrush.

• Craft Knife: A sharp knife or X-Acto blade.

• Mould Release: Mould release spray (or a thin layer of petroleum jelly).

• Holding Tools: Rubber bands, two flat pieces of cardboard or wood, and liquid casting resin.

Step 1: Prepare Your Clay Miniature

1. Clean the Surface: Wipe off any dust, lint, or fingerprints from your baked clay figure.

2. Add Pour Channels (Sprues): Attach a small stick of clay to the bottom of your figure. This creates a funnel path (pour sprue) where you will pour the resin later. Attach tiny sticks or wire to high points (like ears or hands) so trapped air bubbles can escape (air vents).

Step 2: Set Up the Base and Alignment Locks (Keys)

Alignment locks (called keys) are little bumps and dimples that help the two halves of your mould line up perfectly every time.

1. Build the Clay Bed: Fill the bottom half of your plastic box with non-drying oil clay and smooth it out.

2. Press in the Figurine: Press your figure sideways halfway into the clay bed, leaving the top half exposed.

3. Make the Keys: Use a marble or paintbrush end to press 3 or 4 small round dents into the clay base around your figure.

4. First Silicone Pour: Mix your liquid silicone, pour it slowly over the exposed figure inside the box, and let it harden completely.

Step 3: Pour the Second Half

1. Remove the Base Clay: Once the silicone hardens, peel away the bottom layer of oil clay. Clean off any leftover clay residue.

2. Apply Mould Release: Crucial step! Spray or wipe mould release all over the hard silicone surface and the key dents. Without release agent, the new silicone will stick to the old silicone forever.

3. Second Pour: Reassemble your box around the hard silicone, mix a new batch of silicone, and pour it over the top to cover the rest of your figure. Let it cure.

Step 4: Create Side Slits (Cutting Out the Figure)

Once the solid block of silicone is completely dry, remove it from the box.

1. Find the Seam Line: Look for the line where the two silicone sections meet.

2. Cut Wavy Slits: Use a sharp craft knife to cut open the silicone along the sides until you reach the figure inside.

   • Tip: Do not cut in a straight line. Cut in a wavy or zig-zag pattern. These wavy edges act like teeth that lock together tightly.

3. Keep One Side Attached: Leave one side uncut to act as a hinge. Flex open the silicone block and carefully pull out your original clay figure.

Step 5: Cast Resin Clones Using Rubber Bands

Now you are ready to make duplicate figures with liquid resin!

1. Match the Keys: Fit the two silicone halves back together. Make sure all the round bumps and wavy cuts line up perfectly.

2. Add Flat Backing Boards: Place a flat piece of stiff cardboard, thin wood, or acrylic on each outer side of the silicone mould block. This helps spread pressure evenly.

3. Wrap with Rubber Bands: Put rubber bands around the boards and the silicone mould.

   • Getting the Right Tightness: The rubber bands must keep the seam closed so resin does not leak out. However, do not make them too tight, or they will squeeze and distort the shape of your figure inside.

4. Pour the Resin: Mix your liquid resin and pour it into the main hole at the top. Gently tap the sides of the mould to let air bubbles escape through the vent holes.

5. Demould: Once the resin hardens completely, take off the rubber bands, pull open the flexible silicone walls, and pop out your new 3D clone!

Quick Tips

• Extra Lines on Your Cast (Flash): If your resin figure has thin lines along the seams, your rubber bands were too loose. Simply trim the extra resin off with a craft knife and sand it smooth.

• Missing Details: If small parts like fingers are missing, air was trapped inside. Use a needle to poke a tiny air hole from that point to the outside of the mould.