A Mold Rubber Selection Guide for Jewelers

Learn about mold rubber and refer to the included chart to help you find the best rubber for your jewelry designs.

Last edited: 12/11/2020

Mold making allows you to quickly make multiples; it reduces your repetitive work and frees up time for design. Generally used as part of the casting process, molding can help you keep an archive of your work, or the molds can be saved for future production. If you want to make molds for casting and you aren't casting in-house, you can send your vulcanized mold to a caster who will tree and cast the design for you.

Making molds from objects, such as a finished piece of jewelry or a hard wax or resin model, is a simple process:

  • Place about half of the rubber into an aluminum frame.
  • Position your model in the center of the rubber.
  • Press the other half of the rubber over your model.
  • Once the mold is packed, use a vulcanizer to cure the mold; the heat and pressure cures the rubber into a finished vulcanized mold. Follow the recommended time and temperature from the manufacturer for successful results.
  • Once it is cool, you are ready to cut and remove the model from the mold, and then you can begin injecting copies.

The release agents built into silicone mold rubber offer many benefits that streamline your mold-making process. Release powder is not typically needed so your work area stays cleaner and your costs are reduced. Silicone molds produce smoother waxes that need less cleanup before casting. Better waxes result in less finishing time on the casted piece. Other benefits of using silicone mold rubber are:

  • Low shrinkage rates.
  • Faster to pack and prepare the mold for vulcanizing.
  • Master models have less wear and last longer. They do not need to be plated and need less cleaning.

Mold Rubber Comparison Chart

Mold Rubber Item number Usage Cure Time Shrinkage Vulcanization Temp. Durometer
Nicem® Red Silicone 701397 A great all-around rubber that accommodates the majority of jewelry designs. It is slightly more flexible, allowing for easier removal from undercut patterns. The excellent elastic recovery reduces parting lines throughout the life of the mold. If you need more flexibility in a specific region of the mold you can use the purple (701384) as an insert, for items with stone settings etc. 12.7 mins. (per ¼" thickness) 2.5% 356°F (180°C) 42–44
Nicem® Pink Silicone 701380 A great all around general-purpose rubber, with good flexibility and memory; works well for the majority of your designs. It can be used with the purple (701384) to create fixed or removable cores and plugs that need more flexibility to be removed, such as basket settings, charms or small figurines. 12.7 mins. (per ¼" thickness) 2.5% 356°F (180°C) 44–46
Nicem® Light Blue Silicone 701382 This medium-hard rubber is best suited for designs requiring less flexibility to remove, such as flat medallions and coins. It can be combined with the purple (701384) to create fixed or removable cores and plugs for delicate features. 12.7 mins. (per ¼" thickness) 2.5% 356°F (180°C) 44–46
Nicem® Purple Silicone 701384 This softer, flexible, high-tear strength rubber is ideal for inserts and plugs with the 356°F (180°C) rubbers. 12.7 mins. (per ¼" thickness) 2.5% 356°F (180°C) 31–33
Nicem® LTV* Apricot Silicone 701394 This Apricot rubber is a great all around mold choice with a very low shrinkage rate. The durometer is a medium stiffness; it's a good choice for the majority of designs. The LTV* cure temp allows the mold to set at lower temp which works well with hard carving wax and 3D printed models—use the release agent (701985) when molding 3D printed models. If you need more flexibility and easier removal from a specific area of the mold, such as cores or plugs around stone settings etc., we recommend using the reverse electron (701390) for inserts. 19 mins. (per ¼" thickness) .3% 194°F (90°C) 43–45
Nicem® LTV* Transparent Silicone 701395 This rubber is excellent for undercuts and filigree, and a low shrinkage rate makes it a great choice for designs that need less shrinkage, such as rings and items with stone settings. The transparency allows more visibility during cutting and injecting to better identify venting opportunities. The lower vulcanizing temp makes it ideal to mold hard carving wax models; it is also suitable for 3D printed resin models when used with the release agent (701985). The high-tear resistant properties and slightly softer durometer (stiffness) reduce the need for more flexible inserts. 19 mins. (per ¼" thickness) .3% 203°F (95°C) 39–41
Nicem® LTV* White Silicone 701392 This medium-hard, low-shrink LTV rubber is best suited for simple or flat designs with fewer undercuts that require less flexiblity to remove, such as flat medallions and coins etc. 19 mins. (per ¼" thickness) .3% 194°F (90°C) 46–48
Nicem® LTV* Reverse-Electron Silicone 701390 This low-shrinkage, high-tear resistant rubber is specifically designed for molding copper, brass, silver and bronze. These metals have a tendancy to react with many types of rubber during the vulcanization process. Its high tear strength also makes it a great choice for use as an insert or core inside of a harder rubber mold. 19 mins. (per ¼" thickness) .3% 194°F (90°C) 48–50
Castaldo® Super High-Strength Silicone 701113 A high-quality medium-hard rubber with high tear and tensil strength, good for general application including cores and plugs. Can be used with SuperStretch for cores and plugs. 15 mins. (per ¼" thickness) 2.3% 330°F (166°C) 38–40
Castaldo® VLT** Silicone 701005 This very low shrinkage rubber has a low vancanizing temp and it can be used with plastic or resin models, as well as traditional hard carving wax models. 30–90 mins. .1% 160°–190°F (71°–88°C) 38–40
Castaldo® SuperStretch Silicone 7010945 This soft, high-tear resistant rubber can be used as an insert for plugs and cores, or as a high-strength mold that doesn't require the usual cores and plugs. 15 mins. (per ¼" thickness) 1.3% 330°–350°F (165°–76°C) 28
Castaldo® Gold Label® Natural 701148 This natural organic rubber has good flexibility and is ideal for filigree and other delicate designs. 15 mins. (per ¼" thickness) 3–4% 307°F (153°C) 37
Castaldo® White Label Natural 701147 This natural organic rubber is stiffer than the Gold Label® and is suitable for flat or simple designs. 15 mins. (per ¼" thickness) 3–4% 307°F (153°C) 42
Castaldo® No-Shrink Pink Natural 701145 No shrink is a very low to 0% shrinkage organic molding rubber. Note: Extremely precise temp control is required to get to the 0% shrink rate. 15 mins. (per ¼" thickness) 0% 310°F (154°C) 43

*Low-temperature vulcanizing rubber

**Very low temperature