As the name indicates a skin mould begins with a skin. For very small masters this will be enough to cast from. Most mould making applications however, will rely on the addition of a ‘jacket’. A jacket is a structural support for the skin. While the skin holds the detail the jacket holds the form, the jacket stops the casting distorting from the weight of the casting material. A jacket can be made from plaster, mod-roc, jesmonite or fibre-glass (in GP resin).



When making a mould of an master, which is particularly large in size or volume, there would be considerable cost involved in producing a solid silicone mould, and many rigid mould making techniques would be inappropriate for detailed or undercut surfaces.



The skin moulding technique is especially well suited to silicones with high extensibility (can be easily stretched). Your silicone supplier can suggest the best one for you.


Life castings in plaster make perfect candidates to make a skin mould from, because they are usually medium to large in size and volume and have complex detailed surfaces. Below is a real example I have documented to demonstrate this technique. Below is a real example I have documented to demonstrate how to make copies of a live subjects face.


The master we will use for this mould making technique is a plaster casting of a face, captured using an alginate/Mod-roc mould (see life-casting). Although there are skin safe silicones available, the quality of the castings are questionable when compared to the castings taken from an alginate/silicone skin moulds.




How do I make a Skin Mould?


1.The first thing we need to do is place the master (plaster face casting) flat side down on a working board, never use the desk. Using a board allows us to move the mould around as we make it (helpful later).


2.The next step is to mix the first batch of silicone. This will only need to be a small amount, as we will only be concerned with capturing detail at this stage. Once mixed and degassed, pour over the entire face, ensuring it is completely covered. Allow the silicone to flow, do not worry if a little runs off the edge of your board or if it looks very thin. This layer will prevent air bubbles sticking to the inner surface of the mould. You may notice the odd air bubble lying just under the surface, if you do, purse your lips and give it a sharp quick blow, it should pop. This happens more often around eyes nostrils and corners of the mouth so be vigilant.


3.When this first layer of silicone is cured, we need to mix more silicone and de-gas it. At this stage we need to add a thixotropic agent (thickener) to the silicone and stir it in thoroughly until the silicone ceases to run. This is then applied to the first layer in  a circular pasting motion, much like icing a cake. This layer must be as even and as smooth as possible. An ideal thickness for this layer is about 5 mm.


4.Once this layer is cured, a jacket or support structure must be added. This can be made using plaster and scrim, mod-roc or fibre-glass. (See ‘Life-casting’ or ‘GP resin’) The jacket for this mould is made from glass reinforced plastic or fibre-glass as it is more commonly known.


5.Using a pair of scissors cut some ‘tissue fibre-glass matting’ and some ‘course chop-strand fibre-glass matting’ into pieces around the size of banknotes.


6.Mix up some GP resin (see Polyesters- GP resin). Taking a brush, apply a liberal layer of resin directly to the silicone surface.


7.Lay a piece of tissue fibre-glass matting over the wet resin surface and using the brush in a stippling action, press the matting into the resin until saturated. Working from the centre out, ensure all the air bubbles are removed from under the matting (Air bubbles are clearly visible through the wetted matting). The next piece goes on, overlapping the first, wetted down with more resin on the brush, and so on. Continue this until the entire surface has had at least 2 layers of tissue matting. This is where the board is useful as you will be able to rotate the mould on the table so you don’t have to lean over your work. You will NOT need to wait for each layer to set before starting the next.


8.The next step in to de-laminate the course chop strand matting we cut earlier. Although it can be used as it is, peeling the 2 layers of fibre-glass apart is helpful because it makes it easier to apply to a complex form, like a human face. Using the same technique of stippling, wet the matting down, again ensure all air bubbles are evacuated from beneath the surface. Usually 2 layer of this matting is enough for a mould the size of a face. Larger moulds will need more layers to add strength.


9.This step is optional, but recommended as it will save you from potential minor injury. Mix up some gel-coat. Brush it over the entire surface of the jacket in as thick a layer as you can get it.


10. When the jacket has been allowed to fully cure after around an hour or so, remove it carefully from the silicone skin beneath. Slowly peel off the silicone skin, taking extra care around the corners of the mouth where it has a tendency to snag in the crevices. Once removed from the master, place the skin back into the jacket and you are ready to begin casting.

 

Skin Mould

 

What is a Skin Mould?


Skin moulds can be made to almost any size and shape and is one of the cheapest and most versatile forms of mould making. However, it is also one of the most complex and involved mould making methods. This technique is commonly used in industry for reproducing large statues and interior décor features.


A skin mould can be made with silicone, latex or polyurethane rubbers. When using latex to make a skin mould (dependent on the masters surface porosity) it can be dipped or brushed on to build a skin thickness around the master.


Silicone and polyurethane rubber must be poured and spread on to achieve a skin thickness.

   

   

Silicone skin mould making

Multi-part, silicone skin mould with a fibre-glass jacket

   

Multi-part, silicone skin mould with a fibre-glass jacket

   

Brushing a silicone skin mould