Fun with Silicone – A guide to making posable, realistic arms with no specialist equipment

As Theatre of the Damned enters pre-production for their 2011 Grand Guignol show, in-house designer Alice Saville presents the first of several articles discussing the method behind the madness!

When I first started researching making realistic prosthetics, it looked like it would be impossible without a studio, expensive materials and an array of specialist equipment. The ideal material for prosthetics is silicone, since it is durable, waterproof, and has a translucent finish that effectively mimics real skin – but kits for silicone moulding are hugely expensive and intended for workshop use.

The idea of using silicone bathroom caulk isn’t new, but a lot of the methodologies you can find leave out crucial information about how to tint and paint it if you want something more than a basic Hallowe’en scare. Employing a red layer beneath the flesh coloured ‘skin’ layer is a trick beloved of professional prosthetics artists, and it will elevate your arm from the accurate to the uncanny.

These instructions are fairly exhaustive, since I am a perfectionist and spent some time working on this technique. If you want a more basic arm, simply tint all your silicone to the desired colour, fill the mould, then when set apply the nails – the painting and wire skeleton are a bit more fiddly, but essential for a really realistic look.

You will need

Silicone Caulk
Acrylic paint in red, blue, white, brown and yellow
Plaster of Paris
A cardboard shoe box
Aluminium Foil
Vaseline
Sturdy wire, preferably plastic coated (optional)
Artificial nails
A willing victim volunteer


Step-By-Step

1) Prepare your shoe box. The base of the box should be at least an inch, but no more than three inches, longer and wider than the arm you aim to replicate. If a shoe box isn’t long enough, then you can adjust an ordinary cardboard box. Then trim the sides of the box to three inches deep all the way round, and line with foil. Finally, cut a semi circle from the centre of one of the short sides of the box, in which the model’s arm can comfortably rest. Give your model some Vaseline to thoroughly coat their arm.


2) Make up the plaster according to the packet instructions. It is a good idea to use cheap plastic stackable bowls, e.g. from a Pound shop, to mix this and the silicone, as they can be difficult to fully clean. Stir with a stick or dowel, making sure you add as little air as possible. Then pour a thick layer of two thirds of the plaster into your shoe box, up to the base of the semi circle cut out. Working quickly, instruct your model to place their arm in the box, pressing slightly into the plaster, then apply more plaster on either side of their arm. The aim is to mound the plaster exactly half way up the arm, and then to level the surface as much as possible. Help your model stay still while the plaster sets, to get a clean impression – the plaster will get hot, but (unless they are allergic) not uncomfortably so. 


3) Apply a thick layer of Vaseline to the surface of the plaster surrounding the impression, paying special attention to the gaps between the fingers. Place big pieces of tinfoil on the surface, covering with more Vaseline – this will help the two halves of the mould separate later. Then prepare more plaster, and pour it over the model’s arm. This half of the mould needs to be sturdy, so it can be lifted off later, so it is a good idea to mound the plaster up over the model’s hand and arm, so that it is at least an inch thick at all points, rather than attempting to spread it to the edges of the box. Leave to set. Then use a marker pen to draw round the outline of the second half of the mould, as accurately as you can – this is crucial to aligning the two halves of the mould later. Very carefully lift off the top half of the mould to release the model – you can loosen the edges with a palette knife if need be. Don’t remove the Vaseline and foil, though.

Applying the plaster using myself as a model

4) Prepare your silicone. In theory you are meant to have a caulking gun, but I don’t and imagine you won’t either, so just saw off the top of the tube with a knife/saw, and scrape out the contents of two of the tubes into a plastic bowl. An overwhelming smell of vinegar will emerge at this point, so do this outside, or by an open window. You should probably wear a protective mask too. Then mix in enough acrylic paint (white, red, brown and yellow) to make it flesh coloured, but still vaguely transparant – this stage has the dual purpose of a) colouring the arm, and b) injecting the moisture into the silicone which it needs to cure. Unless you mix moisture into the silicone itself, in cannot cure in layers thicker than half an inch.


5) Apply a thin layer of Vaseline to the inside of the mould. Then spread your flesh coloured silicone to about half an inch thick over both sides of the hand impression, going thicker as you move down the arm. This stage is difficult, as it wants to stick to itself not to the mould – a spatula helps. Bear in mind it doesn’t need to be 100% even –the skin is thicker on the heel of the palm, for example, and on the back of the arm. Make sure you go right up to the edges of the mould. Then mix pure red acrylic paint into the remaining two tubes of silicone caulk (you can use the same bowl) and place big dollops of it on top of the flesh coloured silicone, then spread it very gently to the edges of the mould, until it is completely and even filled. 


6) If desired, make a ‘skeleton’ out of garden wire- it should be plastic coated, so that it will bond with the silicone better, and will  not cut through it when posed. This skeleton shape should be a long quadruple length for the arm, attached to a wire circle for the palm, attached to individual double lengths of wire for each finger. Match the wire skeleton to your model’s arm, making the palm and fingers about an inch shorter, and make sure the fingers and wrist can be easily bent as desired.


7) Press the ‘skeleton’ into the surface of the silicone, making sure the wire is exactly central in the fingers, and will not risk poking through at any point. Place the top half of your mould on top of the bottom half, using the marker outline to ensure they are perfectly matched. Leave to set for at least 48 hours. 


8) Remove the arm from the mould. Very carefully trim the edges, if necessary, with nail scissors. Use more silicone caulk to apply the acrylic nails to the finger tips, having trimmed them to size as necessary. Don’t try to use glue for this stage – remember nothing sticks to silicone except more silicone. 


9) If desired, paint the arm. Again, you can only do this using more silicone. Mix silicone caulk with enough white spirit to make a paintable consistency, then tint with acrylic paint. This will probably destroy whatever brushes you use, so use really cheap/busted ones. Resist the temptation to paint it too much, or you’ll lose the translucency that makes it so realistic. Particularly useful touches are subtle blue veins on the wrist, redness on the palms and knuckles, and cuticles on the nails. Probably you’ll also need to touch up any places where the mould didn’t quite touch around the edges. Leave to dry for 24 hours.

Out of mold awaiting finishing and painting

Care of your arm
The completed arm is fully posable, if made with the wire skeleton – however, avoid changing its pose too often, as there is a danger that the wire will start to poke through. The other non-silicone element of the arm, the nails, can also be problematic – it might be worth buying a small squeezy tube of silicone for any repairs needed later. Still, despite these problems, your arm is far more durable than a plaster equivalent. My prosthetic arm was sawn off on stage every night for a month with no real damage, and the blood washed off easily in warm water.

Bracelets and rings can offer crucial continuity for stage or magical use – buy two sets of identical jewellery for the prosthetic and actress. The same mould can be used again and again, and it is easy to vary the skin tone as needed. For examples of some beautiful detailed amateur prosthetic work, I recommend browsing the Replica Movie Prop Forum, to which I owe much of the information given here.

Have fun!

- Alice Saville