FormX is a company specialized in molds and casts for film and cosplay purposes. I decided to bring them a visit in Amsterdam and have a look at the different kind of mixtures they sell for creating human skin imitation. Firstly, they advised me to first create a cast with plaster of a human back from a model. This is done by dipping the plaster in a bucket of water and laying it over the back of the model. The plaster cures in about 10 to 20 minutes and can then be taken off the back. It is important to make this cast since this transfers the rougher texture of the human skin, upon the imitation skin and keeps the layer thin enough for lights to be able to shine through it.
Secondly, FormX introduced me to liquid rubber called Ecoflex 00-30, which is often used for film props to imitate a human body parts. It consists of two liquid parts which can be mixed on a equal basis. You have to thoroughly mix it and it can be poured into the cast (see animation). To give the rubber a more natural look it is mixed with skin-tone pigment. The hardness of these rubber silicons is measured in shore. A shore of 00-30 means the rubber, once cured, is relatively soft and stretchable, which is ideal for our replica skin of the human back. Furthermore this rubber allows for pressure sensors or LEDs to be dipped inside it while curing. Which might help create a more holistic prototype and add to the structural integrity of the build.
For just a replica of the lower back 1kg of Ecoflex 00-30 is precisely enough. For a larger surface area I would advise getting a larger quantity or consider building a under-structure to save money.
The imitation skin will end up as a rubber mat that can be placed on top of our practicing device that holds the vertebrae replicas. This way the device can be pressed and manipulated to the user’s will with largely the same tactile feedback as when massaging a real human.
Observing from the user tests, there are very different attitudes towards the rubber imitation skin. Some people are disgusted by the rubbery feel, others dislike the fact that it is cold (or at least not as hot as a human body) and again others are pleasantly surprised. However there is one thing all users agree on; the imitation skin really adds the feeling you are treating a real person.