Silicone Casting

Silicone Casting

Silicone is a very useful form of plastic that is very flexible once set but returns to its original shape once pressure is removed from it. It is often, like I did, used to make armatures: which are used in animation.

The first step in this process is to make the design for the armature you want to create out of clay. These can be quite detaiked but it is important to mkae sure there are no undercuts so you can get the silicone in everywhere.

The next stepp is to roll out a slab of clay, the same type as before, to around an inch thick, making it large enough to comfortably fit your design inside. Once rolled out you form a divot to place your design inside, around halfway up your design sticking out on top. Make sure to not press your design in too firmly. Smooth the edges between the two.

Using laminated MDF boards you form a box around the slab, holding them in place with clay o the outside. To make sure that there are no gaps you also fill the inside corners and edges with clay. ‘Keys’, little divots, are pushed in to make sure that the two sides correctly line up.

To form the mould for the silicone you mix up some plaster of Paris, making sure to keep the ratios correct. and mix through thoroughly. The mixture needs to be left to thicken for a few minutes, until it reachesa custard like consistancy, before pooring into the base. Whilst waiting for the plaster of Paris to set you are able to wash up and clean all tools used so far, keeping the workstation tidy.

Once the plaster of Paris is set remove the MDF boards and turn over the piece. Carefully peel back the clay slab, leaving your clay desugn in the plaster of Paris. Make sure it is still neat and smooth on the back before reforming the MDF box and filling the gaps with clay. As the next pour of plaster of Paris wil be going onto plaster of Paris releasing gel needs to be generously spread around the exposed plaster. Vaseline is frequently used as a releasing gel in this process. The same method for the plaster is then repeated. I had to miss this part due to being hypo but was so grateful at how Yvonne, the instructor, was so accepting of it and continued my work so I was not behind due to my diabetes. I was able to continue with the process after about 10 minutes.

Once dry you seperate the two halves of the mould and remove your clay design. This is the final mould, which could be reused many times if so desired.

A thin silicone layer, referred to as a skin, is painted in the mould halves carefully, we had to mix silicone with the catalyst (10:1). The catalyst we used contained a red dye to make it easy for us to tell whether or not it was thoroughly mixed in with silicone. It provides the created piece with a slight pink colouring. It is possible to use a clear catalyst that you can then add dyes to make it the colour of your choice, however, it is much harder this way to be sure that the silicone is wholly mixed through.

The silicone skin is then left for at least 24 hours to dry before the process can continue.

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