Injecting Silicone

Now that the mould was as cleaned out as it was going to be, the preparations could begin for the injecting process.

Inserting pipe
The first stage of this was to insert a length of white plumbers tubing up through the inside of the fibre glass head and out through the top. A hole was cut into the top of the head, slightly larger than the diameter of the pipe, before the pipe was pushed up inside so that a tiny bit was sticking out. The hole was then filled with a combination of car body filler and chopped fibre glass strand on both the top and the inside of the head around the piping. Additional car body filler/chopped strand mix was also applied against the inside of the back of the neck to hold the pipe in place at a slight angle. Once this had hardened, the car body filler and extra length of piping needed to be filed down to follow the natural curve of the head. This was a very slow and tiring process as it had to be done manually, however, I was eventually happy with the result.

Drilling bolt holes
Bolt holes were drilled into the flange of the fibre glass mould once it was completed, however, it is recommended that further holes were drilled into both eyes and the mouth as well as around the bottom of the mould to ensure that the mould remains as tight to the head as possible during the injecting process to keep the edges as thin as possible.

Making bleeders
In order to ensure that the injected silicone had spread to all areas of the prosthetic mould, bleed holes needed to be made. This began by filling small tubes (I used tampon casings) with car body filler, waiting for them to harden, ripping the cases off and cutting them down into smaller pieces. These were then attached to the outside of the mould on the highest points of the face and any areas far away from the injecting site (as indicated in image) using more car body filler. The holes needed to be drilled from the inside of the mould to lessen any risk of the gel coat cracking, therefore, the mould needed to be held up to the light to indicate the placement of the bleeders and marked on the inside with a small dot which could then be drilled through using a 2mm bit. Although some of my bleed holes were not completely central, they would still work at releasing small amounts of silicone.

Mould release
To prevent the finished prosthetic from becoming stuck inside the mould and heighten the risk of ripping, both the mould and fibre glass head needed to be covered in some form of mould release. For this I used a 50/50 mixture of washing up liquid and water which was rubbed all over both parts and dried. To release the prosthetic, the mould simply needs to be plunged into water to reactivate the washing up liquid.

Wafer thin flashing
There are two options for creating a thin flashing layer onto the prosthetic; stippling a combination of Plastil A&B silicone all over the head and mould, or airbrushing cap plastic over. I had been told previously that many people had encountered difficulties with cap plastic sticking to the fibre glass and therefore decided to opt for the silicone option.

Preparing syringe 
I had bought a drain plunging syringe from Homebase previously to use in the injection, however, I did encounter a few difficulties with this. The top of the syringe with the pump attached to it was attached to the rest of the piece and would not come apart, it therefore had to be smashed or sawed off and was then difficult to put back together. The inside of the syringe also needed to be thoroughly cleaned out as there was a lot of grease coating all elements of it and this may have affected the cure of the silicone put through it. The plunger piece on the front of the syringe also needed to be pulled off.

Injecting silicone
Once all of these processes were complete, the piece was finally ready for injection! The sections of the mould were bolted back together around the fibre glass head and tightened as much as possible using pliers. It was then placed inside a bucket, or in my case, due to the size, a bin for support. The cleaned syringe was then held into place at the top of the piping using duck tape.
I had previously weighed the clay taken out of the mould and it had come to 1.25kg, taking into consideration the excess clay cleaned out of the mould that was not weighed, and also the length of the piping that also needed to be filled I decided to round up this number to 1.5kg of silicone. Having previously completed some samples of silicone using different amounts of deadener I had decided that 120% would be best as it would create a soft and stretchy piece that would move well with the face, without becoming so delicate that it increased the risk of ripping when it was removed from the mould. With this in mind I used 350g of Platsil Gel 10 A, 350g of Platsil Gel 10 B and 840g of deadener with flesh pigment which made 1,540g in total. Once all of this had been pushed into the mould there were still a couple of bleeders that weren't leaking so I pushed an additional 90g of just A and B through and this seemed to do the trick.