Making a mold seems like a cut-and-dried formula – mix the material, apply it on the mold using the chosen technique and let it set. Once cured, the mold can be used to make the cast.
However, things don’t always turn out as straightforward as they seem. There’s a lot that can go wrong and play havoc with the mold making process. Let us explore some of the common mistakes:
Unmixed material – Most mold making rubbers come as two part systems (liquid latex rubber being an exception). The rubber and catalyst have to be mixed together properly or it will show up as streaks of uncured rubber, soft rubber or even air bubbles. The sides and bottom of the mixing container should be scraped properly to ensure that no unmixed material gets left behind.
Wrong mixing ratio – The container of the material will specify the mix ratio. This has to be followed precisely as any deviation can lead to the mold curing slowly, curing partially, curing softer or even not curing at all. Always double check the mix ratio and reaffirm whether it is by volume or by weight. The latter calls for a weighing scale to ensure complete accuracy.
Not stirring before use – It is literally a hara-kiri not to shake or stir the material before pouring it out for measuring. This is because the material may settle at the bottom leading to soft curing or bubbles in the final mold. Follow the instructions on the package about stirring/shaking prior to use.
Not the right temperature – All materials should be at room temperature when mixing and using. Variance in the temperature of the material can disrupt the cure time or even cause the mold to not cure at all.
Too much release agent – Using a release agent on the model is essential as it always for easy demolding of the mold. However, applying too much of it can interfere with the details and even lead to pinhole surface defects in the mold. Apply a thin and even coat on the model and brush out any excess material immediately.
Short pour time – Every material has a specific pot time, set time, cure time and so on. If the mixing and pouring is done too slowly, it may cross the threshold time and start hardening even before the material is in place. Keep the pour time in mind and opt for a longer interval when making large or complicated molds.
EnvironMolds is the go-to resource for everything to do with how to make molds. The art supplier provides useful information, links, books, videos and even hosts workshops on popular topics. They are also open to providing personal assistance to guide artists through common pitfalls and the like.