Silicone: Why It Fails to Cure and Turns Dark?
Why does silicone fail to cure and turn dark? Learn about cure inhibition, sulfur contact, and proper mold making methods.
Silicone is one of the most essential materials used in mold making during statue production. A flexible silicone mold is generally used to accurately capture every fine detail, curve, and texture of a figure shaped in clay. However, in some cases, it can be observed that the silicone curing process does not complete as expected, meaning it fails to cure within the anticipated time, or that its surface begins to darken over time. Understanding the reasons behind these issues is important both for correct mold production and for transferring the statue's details without loss.
How Does Silicone Cure?
Silicone cures by transforming from a liquid state into a solid structure through a chemical reaction. This process varies depending on the type of silicone. In condensation type silicones, curing occurs through a reaction that begins with the addition of a catalyst and is also affected by moisture in the air. In platinum catalyzed silicones, curing is based on a reaction that starts when two components are mixed in specific ratios. In both types, mixing in the correct ratio, suitable temperature, and a clean working environment are the basic conditions required for curing to complete without issues.
Why Doesn't Silicone Cure?
One of the most common reasons silicone fails to cure is contact with sulfur containing materials. This situation is referred to as "cure inhibition." In particular, some oil based sculpting clays contain sulfur compounds, and platinum catalyzed silicone poured onto this clay fails to cure at the surface where it contacts the clay. In addition, incorrectly set mixing ratios and the catalyst being added in insufficient or excessive amounts are other important reasons that cause silicone to fail to cure. The silicone being past its expiration date, the ambient temperature being too low, or the working area being excessively humid are also among the factors that negatively affect the curing process.
The Effect of Sulfur Contamination
Sulfur contamination is one of the most frequently encountered problems in silicone mold making in sculpture workshops. Platinum catalyzed silicone that comes into contact with a sulfur containing surface stops its chemical reaction in that area. This condition generally shows itself as the silicone remaining sticky, gel like in consistency, and not fully hardening at the contact surface. For this reason, sculptors carefully check the type and content of the clay being used before taking a silicone mold, and prefer sulfur free clay types when necessary. In addition, some workshops apply a separating barrier layer to reduce the risk of direct contact with the clay.
Why Does Silicone Darken?
Silicone darkening or changing color over time can occur for different reasons. In areas where cure inhibition has occurred, the silicone can chemically react with the sulfur containing surface it touched and show a color change toward brown or dark tones. In addition, long term exposure of silicone molds to sunlight and ultraviolet rays can cause the material's structure to deteriorate over time, leading to yellowing or darkening. A similar oxidation process can occur in silicone left under high temperatures for extended periods, which also causes the material's color to become darker.
The Role of Silicone Molds in Statue Production
In the statue production process, once the clay model is completed, the next step is generally taking the mold. Thanks to its flexible structure, silicone can exactly replicate the finest details, curves, and textured surfaces on the clay. Materials such as fiberglass, plaster, or resin are then poured into this flexible mold to carry out the actual production of the statue. If the silicone mold does not cure correctly, it can lead to imperfections, missing details, or rough areas on the surface of the final statue produced from the mold. For this reason, the correct curing of silicone is a critical stage in ensuring the statue looks fully realistic in its final form.
Precautions to Prevent Silicone Issues
A few basic precautions should be followed to prevent issues such as silicone failing to cure or darkening over time. First, whether the clay to be used contains sulfur should be checked in advance, and if sulfur containing clay must be used, an isolating coating should be applied in between. Measuring the mixing ratios according to the manufacturer's instructions and mixing them homogeneously ensures that curing completes without issues. In addition, paying attention to the silicone's expiration date and ensuring the working environment has suitable temperature and humidity conditions are important steps for the mold making process to result in success.
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