The next stage in the process of creating fibre glass head casts was to create a negative of the plaster cast in silicone. For this Paige and I decided to use Tinsil 8030 in preference to Tinsil 7025 as it was slightly stronger and we wanted to minimise the chance of any mistakes, particularly as the silicone and catalyst cost £160 for 11kg!
Before the silicone could be applied to the casts, a clay wall needed to be build around the base of the cast with keys cut into it at regular intervals. This would cause the silicone that ran down off the surface of the cast to pool into this space to create a silicone edge with keys that would later slot more comfortably into the fibre glass jacket. Once the wall was built and all of the keys cut in, the cast was ready for the silicone to be applied.
The first stage in the siliconing process was to apply a layer of unthickened silicone all over the head and into the base and keys to pick up all of the detail in the face. We were initially a little worried about the process of mixing up the silicone with 10% catalyst but received a lot of useful advice from some model making students and learnt that it is important to put the mixed silicone into a pressure chamber to remove any air bubbles before applying it to the cast. The application of the silicone was fairly straightforward, however, we did encounter a few problems in ensuring that the holes drilled around the hairline were adequately filled on the cast of Josh Lonsdale. Unfortunately on the cast of Josh Whorriskey, due to some problems with the alginate application, we had not been able to get an adequate transfer of the hair line to do this. Once we were satisfied that both casts were completely coated in silicone it needed to be left overnight to fully cure.
Once the first layer of silicone was cured the second layer could be applied, this time mixed with a product called Thixotropic to thicken it. This thickened layer was applied only onto the head and shoulders, not onto the base and keys in order to keep the surface of this level. Once the thickened layer was complete and still uncured, small blocks of cured silicone (made using an ice cube tray) were pushed into the surface of the head, predominantly into the back of the head, forehead and shoulders. These blocks would create a greater surface texture for the fibre glass to cling to when the jacket was applied. When I came to do this stage of the silicone process I noticed that some of the unthickened silicone from the previous layer had spilled over the edge of the clay wall and hidden the keys, this is, however, easily repairable by simply trimming away the overspill.
The first stage in the siliconing process was to apply a layer of unthickened silicone all over the head and into the base and keys to pick up all of the detail in the face. We were initially a little worried about the process of mixing up the silicone with 10% catalyst but received a lot of useful advice from some model making students and learnt that it is important to put the mixed silicone into a pressure chamber to remove any air bubbles before applying it to the cast. The application of the silicone was fairly straightforward, however, we did encounter a few problems in ensuring that the holes drilled around the hairline were adequately filled on the cast of Josh Lonsdale. Unfortunately on the cast of Josh Whorriskey, due to some problems with the alginate application, we had not been able to get an adequate transfer of the hair line to do this. Once we were satisfied that both casts were completely coated in silicone it needed to be left overnight to fully cure.
Once the first layer of silicone was cured the second layer could be applied, this time mixed with a product called Thixotropic to thicken it. This thickened layer was applied only onto the head and shoulders, not onto the base and keys in order to keep the surface of this level. Once the thickened layer was complete and still uncured, small blocks of cured silicone (made using an ice cube tray) were pushed into the surface of the head, predominantly into the back of the head, forehead and shoulders. These blocks would create a greater surface texture for the fibre glass to cling to when the jacket was applied. When I came to do this stage of the silicone process I noticed that some of the unthickened silicone from the previous layer had spilled over the edge of the clay wall and hidden the keys, this is, however, easily repairable by simply trimming away the overspill.
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