How to Make Two-Part Silicone Molds for Resin Casting

This tutorial will demonstrate how to create a two-part silicone mold and cast polyurethane resin to replicate a glass bear craft. The tutorial is simple and easy to understand, making it perfect for beginners.

two part silicone mold

Tools & Materials

1. Original model: glass bear
2. Platinum-cured silicone
3. Polyurethane resin + pigment
4. Sulfur-free clay
5. Plastic cups + stirring sticks
6. Hot glue gun
7. Bolts
8. Mold release agent
9. Mold box
10. Ruler

Step 1: Secure the Master Model

According to the shape of the glass bear model, create a parting line using sulfur-free clay, embedding part of the model in the clay. Note: Ordinary clay contains sulfur, which inhibits the curing of platinum-cured silicone.

• glass bear crafts
• fixed glass bear
• embedding clay

Step 2: Set Positioning Holes

Use bolts to create positioning holes in the clay to ensure the two parts of the silicone mold align tightly, producing a seamless casting.

• groove positioning hole
• setting the positioning holes

Step 3: Build the Mold Box

Construct the mold box and seal all seams with hot glue to prevent liquid silicone from leaking out.

• prepare the mold box
• building the frame
• sealing seams

Step 4: Calculate the Required Amount

Measure the length, width, and height of the mold box with a ruler, then calculate the required amount of silicone using the formula: weight = density × volume. It is recommended to use our website's silicone amount calculator.

• measure length
• measure width
• measure height

Step 5: Prepare the Silicone

Prepare the silicone according to the calculated amount, weighing out parts A and B of the platinum-cured silicone in a 1A:1B ratio (by weight or volume) and mixing them thoroughly. Usually, 20-30 Shore A hardness silicone is chosen, depending on the size of the master model.

• addition silicone
• weigh silicone
• mixed liquid silicone
• stirring liquid silicone

Step 6: Vacuum Degassing

Due to air incorporation during mixing, it's recommended to use a vacuum pump to degas the mixed silicone to avoid bubbles in the silicone mold.

vacuum degassing

Step 7: Pour the Silicone

Slowly pour the degassed silicone into the lowest point of the mold box, allowing it to flow naturally until it covers the model. Pouring slowly in a thin stream helps reduce bubble formation.

• pour liquid silicone
• static curing

Step 8: Remove the Mold Box

The silicone curing time varies by brand and ambient temperature, typically 3-5 hours. Once fully cured, remove the mold box.

removing the mold frame

Step 9: Remove the Clay

Carefully peel the clay away from the model and clean the model with alcohol. Do not separate the model from the silicone mold at this stage.

• peeling clay
• one part silicone mold
• wipe the glass bear

Step 10: Rebuild the Mold Box

Reassemble the mold box and spray it with a mold release agent. The release agent is essential to prevent difficulty in separating the silicone after curing.

• rebuild the mold box
• sealed mold box
• spray release agent

Step 11: Make the Second Part

Repeat steps 5 to 8, mixing and pouring silicone to create the second half of the mold.

• pour in silicone
• wait for the silicone to cure
• demolding mold box

Step 12: Separate the Mold

Carefully separate the two parts of the silicone mold and remove the original glass bear model. Thanks to the excellent release properties of platinum-cured silicone and the release agent, this should be an easy process.

• separation silicone mold
• take out the glass bear

Step 13: Assemble the Mold

Reassemble the two parts of the silicone mold, securing them with rubber bands. The positioning holes created in step 2 will ensure proper alignment. For larger molds, use non-elastic straps to prevent deformation during casting.

• combination mold
• bundle mold

Step 14: Prepare the Resin

Weigh parts A and B of the polyurethane resin in a 1A:1B ratio (by weight or volume) and add the desired pigment, mixing thoroughly.

• weigh the pu resin part A
• weigh the pu resin part B
• add pigment
• stirring polyurethane resin

Step 15: Pour the Resin

Pour the mixed polyurethane resin into the mold. Fill about a quarter of the mold and then vibrate or rotate it to ensure the resin covers every detail of the model. Polyurethane resin has a short working time, so mix and pour quickly.

• pour polyurethane resin
• rotary mold
• casting polyurethane resin

Step 16: Remove the Mold

To check if the resin is cured, leave a small amount in a plastic cup and touch it to test its state. If cured, you can demold the cast resin product.

• verify polyurethane resin curing
• take out the resin crafts
• polyurethane resin crafts

By following these steps, you can easily create high-quality two-part silicone molds and replicate exquisite glass bear crafts. We hope this tutorial is helpful to you, and happy crafting!