What are they made from? - Its important!
There are two types of silicone in common use for mould making - Condensation Cure (sometimes called Tin Cure) and Addition Cure (sometimes called Platinum Cure).
Condensation Cure is cheaper and is therefore more popular. However it is often overlooked that almost all resin manufactures recommend against its use when casting “clear cast” or “water clear” resins. Even when the silicone is fully cured, it still retains moisture at a level that can easily lead to casting failure, in that the resin will not set properly. Just stirring most PU clear resins with a wooden stick is enough to introduce too much moisture into the equation, moisture being the single most common cause of clear resins failing to set properly, apart from mixing the resin incorrectly to start with.
On the other hand, Addition Cure does not suffer from that problem and is the type recommended by almost all resin manufacturers for casting clear types of PU resin. It’s a bit more expensive but it means that the same mould can be used for every type of resin, not just the opaque ones, which when casting around a tube, clear resin is usually the whole point, is it not?
Consequently, all of our moulds are made from Addition Cure silicone.
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