Smooth-On’s Crystal Clear®Urethane Resin is used for thousands of industrial and art-related applications around the world, both large and small. This sequence demonstrates making a two piece silicone mold using Mold Star®15 silicone rubber and Crystal Clear®200 to cast a perfect replica of a conch shell.
In the step-by-step gallery below, you will learn how to make a 2-part mold and casting of a conch sea shell using Smooth-On mold making and casting materials.
Mold Star®15 platinum-cure silicone rubber
Ease Release®200 release agent
Crystal Clear®200 optically clear urethane resin
Ignite®fluorescent color pigments
Reynold's Sculptex®sulfur-free modeling clay
1 - The mold will be made from an original, dry conch sea shell. Front view - notice the cavity in the front.
2 - The conch - back view.
3 - Four acrylic mold walls will be assembled together and adhered to a base surrounding the conch. Try to allow at least 0.5'' space between the original model and the mold walls.
4 - Fit the mold walls together.
5 - Secure the mold walls together using hot melt vinyl.
6 - The 4 mold walls have been assembled and positioned appropriately on the base.
7 - A border is drawn around the edges of the inside of the assembled mold walls so we will know where to place the clay bed for making the first part of the 2-part mold.
8 - Sculptex non-sulfur clay is used to build the clay bed for making the first part of the 2-part mold.
9 - Begin to lay down the bed of clay within the border outline that was drawn previously.
10 - Continue to build up the clay until it is high enough for the first part of the mold.
11 - Make sure to trim the clay bed so that it fits within the pre-assembled mold walls.
12 - The conch will rest in this part of the clay bed while mold rubber is poured around it.
13 - A parting line has been pre-determined and is drawn on the model. The line represents where the two molds halves will separate with least resistance.
14 - Additional view of drawn seam line on conch.
15 - The conch shell has a deep cavity that needs to be addressed. If liquid mold rubber were allowed to fill this undercut, the cured rubber mold would be impossible to remove (also known as mechanical lock).
16 - To prevent mechanical lock, Sculptex non-sulfur based clay is used to fill the cavity.
17 - Place the conch cavity-side down onto the clay bed that you made.
18 - Since the conch is not level we need to lay down more clay to continue to block the cavity and create the first part of the 2-part mold.
19 - Continue adding clay and follow the seam line that you drew with the clay.
20 - Smooth out the clay so that the 2-parts of the mold will join together tightly.
21 - The first part of the mold is almost ready to be poured.
22 - Acorn nuts are added to the clay bed to act as registration keys for the 2 parts of the mold.
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25 - Be sure that the clay is flush against the mold walls to prevent the rubber from flowing behind it.
26 - Secure the mold walls to the base with hot melt vinyl.
27 - Mold Star 15 platinum-cure silicone rubber is used for making the mold. Mix ratio is 1A:1B by volume.
28 - Pre-mix part B before dispensing.
29 - Dispense part A.
30 - Dispense equal parts B.
31 - These will be used to make the 1st half pour.
32 - Pour parts A into larger container.
33 - Pour parts B into the same larger container.
34 - Mix thoroughly until color is uniform.
35 - Mold Star 15 pot life is 50 minutes.
36 - Pour 1st half of mold in a long, thin stream to avoid air bubbles
37 - Allow 1st half of mold to cure for 4 hours.
38 - After 1st half is fully cured, separate from base.
39 - Flip the 1st half of the mold over.
40 - Remove clay from model but do not remove original model from mold rubber in the process.
41 - Remove registration keys (acorn nuts).
42 - A clay plug is rolled to make a pour spout.
43 - The clay plug is positioned on the model.
44 - Ease Release 200 is applied to cured silicone as a separator.
45 - Additional Mold Star 15 for the 2nd half pour is measured and dispensed.
46 - Rubber is mixed thoroughly until color is uniform.
47 - 2nd half of mold is poured.
48 - Rubber is allowed to cure for 4 hours.
49 - Carefully remove mold walls and any clay from fully cured mold.
50 - Use fingers to help part the 2 halves of the mold.
51 - The 2-part rubber mold separates easily.
52 - Gently remove the original model from the mold.
53 - Crystal Clear 200 clear urethane resin is used to cast into the mold. Mix ratio is 100A:90B by weight.
54 - Dispense part A.
55 - Dispense part B.
56 - Thoroughly mix the resin.
57 - The mold is reassembled and a funnel is inserted into the pour hole to help minimize spills.
58 - Crystal Clear is poured into the funnel.
59 - Rubber mold containing resin is placed in pressure pot and subjected to 60 PSI (4.22 kg/cm2) pressure until the resin cures (16 hours).
60 - Pressure casting resins is optimal for creating castings that are truly bubble free.
61 - Demold - cured casting is removed from the mold.
62 - 2-part Mold Star 15 mold with Crystal Clear 200 casting.
63 - Casting is an exact copy of the original and reflects perfect detail captured by the Mold Star 15 rubber.
64 - Another Crystal Clear casting is made. This time a drop of Ignite purple tint is added to the resin for a dramatic finished effect.