Mould making tutorial, Part 1 - Intro

I'm starting to make another silicone mould, for this 17 cm polymer clay human figure I just finished. I'll try to document the whole process, with both images and text. So, I hope when the mould is ready, I'll have a nice little mould making tutorial here.

Intro

Mould making really isn't that mystical or complicated. If one can get the materials and is careful enough to plan ahead, everything should go OK. Should, as there are countless oportunities for things to go wrong. I know, I've made some mistakes over and over... But, I'm trying to learn from my own mistakes, that's one reason I'm trying to document the whole process here.

The process I'm describing here is pretty low key, it doesn't need any air compressors or vacuum tanks. Of course, it's cool if one can remove air bubbles from the silicone with tank, but it really is possible to make moulds without them. Most of the process is still exactly the same.

Choices and options

The easiest way to make a silicone mould is simply to put the original object inside the box, fill it with silicone, let it set and then cut it open just as much as it's possible to remove the original. This method actually works, at least with simple objects with no undercuts. But cutting the silicone open can still be pretty tricky, if one does want to get the original out in one piece. Also, there will be no air vents or syncro details - they all must be made with Exacto-type knife in the cutting process. So, it looks easy, but will it work? Not always.

Better way to make box moulds is to "sink" the original's one half to the clay, to make syncro details (like half-spheres, for example) and air vents to the clay's surface, to surround it with some kind of border and to pour silicone over it. This forms one side of the mould. When silicone is cured, all this will be flipped, clay will be removed, silicone covered with vaseline and second side will be poured.

Box mould is simple, but it takes a lot of silicone, so i'ts expensive and also not that rigid or stable, when the object is bigger - silicone just is a wobbly material. Still, when spending on silicone is not a problem, box mould works very well, especially with smaller objects. The important plus is also that it's easy to recycle older mould pieces as a filler to new moulds.

For bigger sculpts there's another and better type of mould, which takes several times less silicone. This way the thin silicone layer is covered with plaster or resin shell. Making of it is much more complicated and time consuming process, but the result is worth it. It's also possible to use the same plaster cover for different silicone moulds. Like, for different statues with the same basic size and form, but with different details.

The mould I'm trying to make here, is matrix mould.

Next: Part 2 - Base