Molding
& Casting

Molding and Casting is a two-step technique used to create exact replicas of an object. Think of it as creating a "stamp" and then using it to make multiple copies — a process refined by civilizations for thousands of years and now accessible in any Fab Lab.

For the group assignment, I worked alongside Andres Mamani at the Fab Lab Universidad de Lima. My specific contribution was documenting the creation of a silicone mold using a master model found in our laboratory: a Chavín de Huántar "Cabeza Clava" — an iconic piece of ancient Peruvian art.

↗ Andres Mamani's Documentation

To replicate the Cabeza Clava, we used SILIKA CAUCHO SILICONA RTV TIPO 6 combined with its specific Catalyst. This material is preferred for its high fidelity in capturing textures and its ease of use for manual casting.

We measured the mold's capacity by filling it with water to estimate the required volume. Based on this, we calculated the amount of silicone needed, intentionally adding a small surplus to ensure the master model was completely covered.

The RTV Type 6 silicone requires a precise mixing ratio of 2% to 3% catalyst by weight. For every 100g of silicone base, we used a precision scale to add exactly 2g to 3g of catalyst. This precision is essential to ensure the material cures correctly and achieves its full mechanical resistance.

We mixed both components slowly and thoroughly for about 3 to 5 minutes, scraping the sides and bottom of the container to ensure no unmixed base remained. Unmixed material would prevent the mold from curing properly.

Once mixed, we had approximately 15 to 20 minutes to pour the silicone over the master model before it began to thicken. We poured from the lowest point of the mold box, allowing the material to rise naturally around the piece to minimize air bubbles.

We tapped the mold against the table so that any trapped bubbles would rise to the surface. The mold was then left to cure at room temperature for 4 to 8 hours depending on ambient temperature.

As part of my group contribution, I documented the properties of all silicones and resins used. Since these are Peruvian-origin products, formal international data sheets are not widely available — the information below is based on regional product specifications and manufacturer guidelines.

Technical Parameter	Detail
Mixing Ratio	1:1 by weight (use a precision scale)
Pot Life	2 minutes (at 23°C)
Hardening Time	5 to 10 minutes
Demolding Time	15 to 30 minutes (thicker pieces demold faster)
Final Hardness	70 Shore D
Viscosity	Very low (similar to water) — excellent for fine details
Linear Shrinkage	< 0.1% (very low)

Technical Parameter	Detail
Mixing Ratio	1:1 by volume
Pot Life	10 to 15 minutes
Viscosity	Low / Medium (self-leveling)
Touch Dry	12 to 16 hours
Total Cure (>0.5 cm)	Up to 24 hours
Total Cure (<0.5 cm)	Up to 48 hours

A food-grade, platinum-cured RTV silicone rubber ideal for high-precision molds and special effects. Its semi-translucent appearance and soft 10 Shore A hardness make it extremely versatile for detailed reproductions.

Technical Parameter	Detail
Type	Platinum-Cured RTV Silicone
Hardness	10 Shore A (highly flexible)
Mixing Ratio	1:1 by weight or volume
Working Time	15 to 20 minutes
Curing Time	4 to 6 hours (heat acceleratable)
Heat Resistance	Up to 250°C

Technical Parameter	Detail
Type	RTV-2 (Room temperature vulcanization)
Hardness	20 Shore A (ideal for undercuts)
Mixing Ratio	2% to 3% catalyst by weight
Color	White base / colored catalyst
Working Time	15 to 20 minutes (at 23°C)
Curing Time	4 to 12 hours (weather dependent)
Viscosity	Medium (excellent detail registration)

Technical Parameter	Detail
Type	RTV-2 Condensation-cured (tin-based)
Mixing Ratio	2% to 2.5% catalyst by weight or volume
Working Time	15 to 25 minutes
Curing Time	2 to 6 hours
Flexibility	High elasticity for easy release
Compatibility	Polyester, Polyurethane, Epoxy, Plaster, and Wax

I started by creating a 50mm base circle on the XY plane, then applied a 10mm extrusion with the Taper set to 0. The key "magic" step was applying a large 4mm fillet radius to the top edge, creating a smooth dome that looks organic and provides a perfect draft angle for demolding.

On the top face, I sketched a pentagon, connected all corners with lines to form the star shape, then used the Trim tool to cut the internal overlapping lines — leaving a clean 5-pointed star. It was extruded 3mm upward (Taper at 0), then finished with a 1.5mm fillet on all top edges to achieve the "puffy" jewelry aesthetic.

In the center of the star surface, I drew a large circle and a slightly offset smaller circle overlapping its top edge — this classic two-circle technique creates a crescent moon silhouette. The main circle was extruded 1.5mm, then filleted to maintain organic consistency. The same process was repeated for the 4 decorative gems.

To prepare for silicone casting, I designed a surrounding box frame to contain the liquid silicone during pouring.

Slicing in Chitubox

I used Chitubox to bridge the gap between my design and the printer. It helped me set up the supports and check every layer to ensure the master model was perfect for molding and casting.

First, I picked the printer profile and used the basic resin profile.

I clicked the plus (+) symbol to load my STL file directly into Chitubox.

In the Print tab, I set the Layer Height to 0.05mm (50μm) — ideal for capturing high-resolution detail with an almost invisible layer line.

I switched to the Support tab and used Autosupport with Medium strength for stability. I intentionally oriented the print so all support marks would land on the back face, keeping the decorative front completely pristine.

I hit the Slice button and Chitubox processed 300 layers. Just like in Bambu Lab, I could check the layers one by one before saving to USB.

The model was exported as a .ctb file to a USB drive and transferred to the SLA printer. After confirming the settings and initiating the print, twelve hours and fifteen minutes later, the high-quality master model was complete.

SLA resin is toxic — nitrile gloves are mandatory. I unscrewed the build platform from the machine to gain better leverage, then used a metal spatula to carefully detach the printed model from the perforated plate. I also cleaned any residue from the plate to avoid accidents and ensure future prints come out cleanly.

I decided to remove the supports before rinsing. Since the "green" uncured resin was still soft, supports could peel off more easily. In hindsight, rinsing first might have softened the attachments further — a useful lesson for next time. My earlier decision to place all supports on the back face successfully kept the front details completely pristine.

The model went into the washing station for 8 minutes. The machine agitates isopropyl alcohol around the part, cleaning all leftover liquid resin from intricate details.

The part entered the curing station, which uses UV light, heat, and a rotating platform to bring the resin to its full mechanical strength. This step is critical before using the model as a master for silicone molds.

After curing, the back had visible support marks and small pits. I used a dual-refinement method to achieve a mold-ready surface:

For the molding phase, I used RTV-F 20 Plus Silicone from Silicon Perú — a condensation-cured tin-based silicone ideal for high-fidelity molds. Its medium viscosity and 20 Shore A flexibility allow demolding of complex shapes without tearing. I chose this silicone because it is particularly effective for projects requiring durability and a faithful reproduction of original textures.

Product Specifications

• Silicone Type: RTV-2 Condensation-cured (tin-based)
• Shore Hardness: 20 A (Flexible and elastic, ideal for parts with undercuts)
• Mixing Ratio: 2% to 3% Catalyst (e.g., 100g of silicone + 2g or 3g of catalyst)
• Base Color: White; Catalyst Color: Transparent, Red, or Blue (depending on batch)
• Working Time: 15 to 20 minutes (at 23°C)
• Curing Time: 4 to 8 hours in warm weather / 8 to 12 hours in cold weather
• Heat Resistance: Up to 200°C — suitable for resins that generate heat during curing

I measured the mold's capacity by filling it with water: 45g (45ml). Since silicone has a density of 1.2g/ml, this required 54g of base (45ml × 1.2g/ml). I prepared 60g of base as a safety margin to compensate for material lost on container walls. Based on 60g, I used a precision dropper to add between 1.2g (2%) and 1.8g (3%) of catalyst with high precision.

The I applied a release agent (desmoldante) into the mold, spreading it thinly and evenly to prevent the silicone from bonding to the piece or the box.

Thorough mixing for 3–5 minutes, scraping the sides to ensure a uniform blend. Once ready, I poured the silicone from the lowest point of the box to let it rise naturally, then tapped the mold against the table to force trapped air bubbles to the surface.

The mold cured at room temperature for about 2 hours. Since I had applied a proper layer of release agent beforehand, the extraction process was successful and the mold remained in excellent condition.

I also decided to create two molds as a precaution. This proved to be a smart move because the first one had a small hole on the left side—likely caused by a trapped air bubble during the pouring process—while the second one came out flawless.

To bring the Sailor Moon transformation brooch to life, I used a vibrant pink soap base — perfect for capturing the magical aesthetic of the original designs.

I used a cheese grater to shred the soap block into fine flakes. Grating is vital because it allows the material to melt much faster and more evenly, preventing hot edges and a solid center.

The flakes were heated to exactly 60°C — at this temperature the soap becomes fully liquid and pourable without losing its vibrant color or generating excessive bubbles.

Because the brooch molds have very intricate details (stars, the crescent moon), I used a funnel for precision pouring — ensuring the liquid reached every corner of the silicone mold without spilling.

After approximately one hour of cooling, I carefully removed the pieces. The results are fantastic — high-detail pink soap that perfectly replicate the SLA-printed master models.

Since the F20-Plus silicone is heat-resistant up to 200°C, I decided to experiment with scented aromatic wax. I had several packs of aromatic wax available, and I chose the blue pack — not only for its wonderful scent but because blue is my favorite color.

I used a small dedicated oven to melt the wax blocks, monitoring until they reached a fully liquid state. The aroma filled the entire room during the process.

To maintain control over the small mold details, I transferred the melted wax using spoons rather than a pour. This allowed me to fill each cavity carefully without overflow and with a clean finish for each piece.

Wax cools much faster than soap. After only 30 minutes, the wax had fully solidified. The mold's flexibility meant the pieces popped out easily, leaving beautiful solid blue aromatic brooches.

After working with both casting materials, the differences became clear.