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After thoroughly cleaning and trimming down the moulds, the GFA (gel-filled appliances) are ready to have silicone poured in. Firstly, Vaseline is added all over the mould to act as a release agent. Couch roll is then used to stipple away any excess; stippled and not wiped away, as the texture might show up in the silicone. Then the tissue thin edge for the prosthetic needs to be created. This is called a proplastic plus polyeurathene suspension and is a mixture of IPA and proplastic plus in a 3:1 ratio.  

Filling the Moulds

  • The mixture should be runny, not stringly and is used to encapsulate the silicone

  • In industry, they airbrush this mixture onto the mould but it can be drizzled and painted on

  • It can be hair dried to speed up the process, but not on a high heat setting

  • 3-4 layers should be done, but if it was airbrushed, 10 layers would be needed, as it would be a lot finer and more even

  • When the layers are finished, use a needle to gentley pick at the edge to check it holds together

  • Oil paint, silicone based makeup or silicone pigment can all be used to colour the silicone. We used silicone pigment, which only requires a tiny amount on the end of a mixing stick. 

  • Be sure to use a seperate stick for each part.

  • To retain transparency, mark a dot in permanent marker at the end of your mixing stick. This way, when you mix in the pigment you should still be able to see the dot through the mixture so you know  you haven't added too much. I added too much on my first mixing, but learned to add a lot less the next time which helped me achieve a lot more translucency.

  • We then added 2 small scoops of flocking (small fibres, which were red to give different colour qualities and a more realistic skin tone) to part A

  • When all this is done, mix all three parts together and pour it into the mould.

  • It should be carefully dribbled, first into the flashing and then around the negative area. It can be moved and distributed with cotton buds.

  • The best way to get it really even, smooth and with thin edges is to use a taping knife, scraping twice and not using a lot of pressure.

  • When you're pleased with how it looks, it should be left to cure which takes approximately 30 minutes. It can be put in the fridge to slow the curing process.

  • 3 more layers of the proplastic plus polyeurathene suspension should then be painted over the silicone.

  • When the layers are dry, the piece is ready to be removed.

Because this process is totally new to me, I found elements of it quite confusing. As I don't really uderstand how the parts work together (how one affects another, the curing process, etc.) I found it very confusing to know how much deadener you're meant to want to add to your mixture. Obviously you have to take into consideration what kind of piece you've sculpted, where its going to be positioned, but I don't know how to work out how squidgey I think it should be. I assume that will come with practise. I think my pieces look ok. After scraping them with the taping knife it looks like the edges will be really thin which is good. Working with silicone for the first time was very odd, and it felt different to how I expected. Its a process that I think will become easier the more i'm familiarised with it and the materials.

Silicone Deadener Calculator. [online image] Available from: http://www.makeup-fx.com/siliconemaths.htm [Accessed: November 6th 2014]

  • Adding deadener/softener will decide how soft/hard you want your prosthetic to be

  • It should never be more than 200%. For example, if you had 100g of part A, 100g of part B and added 200g of softener (part C), then the silicone is 100% deadened. 

  • I found this can be difficult to figure out, but there are plenty of onine calculators that can work out the amounts of all the parts you need to add according to the percentage you want your pieces to be deadened.

  • I deadened my pieces 200%, using 12.5g of part A and B and 50g of part C (deadener).

  • Its very important to label the cups during this, as contaminated silicone can't be used. 

Shore Scale. (2011) [online] Avialble from:http://www.smooth-on.com/Documents-Duromete/c1351_1370/index.html [Accessed: October 29th 2014]

The Shore Scale is used to determine how soft/hard you want you prosthetics to be. Obviously the softer they are, the more flexible and usually more realistic they are. 

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