What You’ll Need

• Sharp craft knife or scalpel
• Permanent marker or fine-tip pen
• Cutting mat or protected work surface
• Thin, flexible ruler (optional for straight cuts)
• Fine talcum powder (optional for tacky surfaces)
• “Pure Mould” – Translucent Liquid Silicone Rubber for Mould Making (ideal if you’re preparing your own moulds requiring a translucent view for precise cutting)
• “Liquid Mould” – Casting Liquid Silicone Rubber, 5-40 Shores, Bi-Component A+B (suitable for detailed, small-section moulds that may require careful splitting)
• “Liquid Mould” – Casting Liquid Silicone Rubber, 15 Shores 20.8 kg (best for advanced users with larger or more technical forms)

Essential Cutting Tools for Silicone Moulds

Always choose a high-quality, sharp craft knife or scalpel when cutting silicone moulds. Precision tools give you cleaner lines and reduce the risk of damaging the fine detail within your mould. Using purpose-made blades designed for flexible materials helps ensure accuracy and keeps your hands safe.

Step 1: Plan Your Cut

Before cutting, study the mould to identify where the seam should run. Look for natural grooves or less-visible areas that will help hide the cut on finished pieces. For complex shapes, consider a zig-zag or keying pattern to ensure your mould aligns perfectly after cutting.

Use a permanent marker or fine-tip pen to lightly mark the planned cut line. Take your time with the design—this is especially important for detailed models or when using a translucent mould made with “Pure Mould” – Translucent Liquid Silicone Rubber for Mould Making, as its clarity assists in guiding your cuts and checking the position of embedded objects.

Step 2: Make the Initial Incision

Place the mould on a stable, protected work surface such as a cutting mat. Select a sharp craft knife or scalpel for the cleanest results. Begin at one end of your marking, gently inserting the blade and following your line with a steady hand.

Always use a sharp, clean blade to prevent dragging or tearing the silicone. For thick or dense moulds—like those made from “Liquid Mould” – Casting Liquid Silicone Rubber, 15 Shores 20.8 kg—start with a shallow incision, ensuring you do not slice too deep in a single pass to avoid damaging the original model inside.

Step 3: Continue and Deepen the Cut Gradually

Work slowly along the marked seam, allowing the blade to do the work with minimal force. It is safer to make several shallow passes rather than one deep cut. This reduces the risk of unwanted splits or accidental damage to mould details.

Avoid cutting too deep in one go. For two-part or thick-walled moulds, gently flex the silicone apart as you go to ensure the blade follows the planned path and doesn’t wander.

Step 4: Completing and Separating the Mould Halves

Once the incision is complete, carefully separate the halves by gently pulling the silicone apart. If the cut catches or sticks, check for any remaining connections along your seam and free them with small, controlled cuts. Dust the cut faces lightly with fine talcum powder if there is any tackiness, particularly with fresh moulds.

At this stage, clean up any rough edges. Flexible silicone moulds produced from “Liquid Mould” – Casting Liquid Silicone Rubber, 5-40 Shores, Bi-Component A+B or “Pure Mould” – Translucent Liquid Silicone Rubber for Mould Making are generally easy to separate without tearing due to their mechanical strength and elasticity.

Tips, Common Mistakes, and Troubleshooting

• Mark and plan your cut line before you start: This prevents wonky seams and alignment issues in your finished casts.
• Work slowly and gently to avoid tearing: Haste or excessive force may cause jagged cuts or damage intricate details.
• Lubricate the blade with a drop of soapy water for smoother cutting in dense or sticky moulds.
• Dust lightly with talc if the mould is tacky: This helps the cut faces release cleanly and prevents them from sticking together afterward.
• Sharpen or replace your blade regularly for crisp, clean edges.

Expert Advice on Cutting Success

Cutting silicone rubber is a skill that improves with practice. Always test your cut technique on a spare or offcut before working on your finished mould. If possible, work in bright, even lighting to make following your marked line easier, especially when using translucent silicone. Clean tools and a tidy workspace make a noticeable difference to your results.