Professional Practice : Silicone Casting!

This was my desk when I first started on the puppets!

Simon had already sculpted the arms, legs and head for the puppets and made an arm mould. These are the arms that he casted.. and then asked for my help!

I was shown how to make simple wooden armatures with kebab sticks in the arms and he'd used popsicle sticks cut into a palm shape and sandwiched wire for fingers between the wood. The arm mould was made with Transil 20 silicone, but it was very soft.

I used Mann Ease Release spray to ensure the silicone didn't stick to the mould. I sprayed two light layers into the mould, waiting for it to dry between layers. I also put chain in the mould through the holes and held up with wire. This chain will be pushed into the silicone body to attach the arms.

I used Platsil Gel 00 to cast these arms. Once both sides were filled with silicone, I waited until it had set slightly and put the armatures in. I waited so that the armatures didn't sink to the bottom and show through in the cast. I then quickly press both sides together as it is a two part mould.

The problem with using silicone for a two part mould is that it is difficult to get a clean seam. The seam on the arms was very thick and even after carefully seaming each arm it was still quite obvious that a two part mould had been used.

While I was casting arms, Simon made a leg mould with Platsil 7325. This was better than the transil 20 mould but they still had very noticeable seams. To save on silicone and weight I put foam into the leg moulds.

Instead of using wooden armatures I tried using wire instead. I wrapped it around the pegs on the board and when I took it off twisted the fingers. These new hand armatures worked a lot better than the last. The wooden ones snapped after a lot of use.

We were having a lot of issues and seemed to be getting nowhere with the seams, so Simon organised a trip to Bristol to visit Andy Spradbery's studio. He's done a lot of model and puppet making for Aardman (http://www.imdb.com/name/nm3434423/). He kindly offered to show us around and give us some advice on making the puppets. After a long day of lots of useful tips and information and some fairly cryptic diagrams we had a new direction to go in with the puppets.

The first thing we did was make a new arm mould using resin instead of silicone. This means that I can clamp the mould together and push out any excess silicone through a small air hole. Instead of setting it in clay, Simon suggested I float the arms using wire and pour the resin carefully underneath the arms first. Once that layer was dry I sprayed it all with release agent and poured the other half. This was risky but it worked! He didn't want to set the arms in clay because often the heat of the resin will cause part of the leg to shrink which gives a slightly uneven seam.

The new arm mould worked so much better. There was still a seam but it was so much smaller and much easier to hide.

Simon had already sculpted the head and gave it to me to make a mould with. This would be a one part mould made with transil 20. We made the decision to make it out of transil 20 and not platsil 7325 because being able to see inside the mould would be very useful with the head because we will be putting a pvc tube into the mould to make a cavity inside the head and it needs to not touch any of the sides. With a translucent mould we can easily see if it touching any of the sides or not.

I glued the head to a square of mdf and sprayed a two layers of release agent. I then built up a wall around it with foam board. I covered the foam board in parcel tape on the inside walls because Andy Spradbery had told us that this will stop the silicone being matte and it will be a translucent mould. Unfortunately this didn't make much of a difference and the mould did come out quite cloudy, but we were still able to see if the tube was touching the sides when we casted it. I think it wouldn't have been cloudy if I had used a degasser, but unfortunately I didn't have access to one as I was doing all of the mould making and most of the casting over summer.

Had to move into Simons office from the portacabin because the weather was so hot that the temperature in the cabin was too high to store the silicone in and it was setting before we'd even finished pouring the cast. We also managed to get our hands on an air conditioner so we were able to keep the temperature of the room down to 18˚

This is manny's body sculpt about to be moulded. The tube in his neck would also be inserted when casting to keep it hollow so there is space for the neck and neck mechanism. Glenn's body was done in the same way, just without the enlarged genitalia and massive belly...

We decided to make a new leg mould because the last one didn't have feet, which Lex our costume designer wasn't happy about and also the seam was still pretty bad. This mould was done with resin, just like the arms. I floated the leg on cocktail sticks instead of wire this time, and they would become the small air holes for the silicone to be pushed out of. I also only did one leg as it could be used for both sides of the body.

This is the head mould in use. The pvc tube is pushed in to make a cavity in the head so that the neck mechanism can be fitted inside. I casted the heads with transil 20 and flesh pigment. Other characters had tan pigment or a mixture of both.

This is one of Manny's arm moulds. I found painting the silicone in first stopped any air bubbles forming in the fingers. I made the tiny hand armatures by wrapping a length of wire around my little finger and then measuring each finger in the mould and twisting it around.