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How Do You Make A Silicone Flat Mould?

Ultimately, the process begins with a flat surface and clay. Non-drying (oil based), sulphur-free clay is the best to use for this method, non-drying will give you literally all the time in the world to work on your sculpture! It’s easily manipulated between your fingers and softens with warmth. 

Clays containing sulphur can inhibit the surface cure of silicones, this is something to be aware of when selecting clays. Our range of oil based clays are sulphur free. 


Oil Based Clay

For beginner level, Soft grade clay is slightly easier to work with, if never handled oil-based clays before.  

The higher the grade, the tougher it is to work with, but holds detail! This isn’t something you need to worry about at this point, soft grade will help you get the feel of working with clay if new to this. 

You can use a tile, MDF wood sheet – any flat surface you have handy, providing it gives you enough space to sculpt in the centre, and enough space around this for your moulding walls.

So to begin, on your flat surface start placing your clay - don’t start off raising this too high – you want enough depth to sculpt a cut, gunshot wound, slash, whatever your idea may be into it, but not so there is an obvious step of clay. Begin by applying small parts of clay to your surface and continuously adding to get your desired shape.

It’s important to know and remember, however the clay looks and sits on the surface; the height of it, texture, etc. will all translate exactly that way into your prosthetics. The reason I say not too high, this will look far too raised on the skin, keeping the clay as flush to the surface as you can, will provide undetectable edges on application.ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ

Once you’ve got a base layer and it’s smooth to the surface, you can then begin to refine - You can go in at this point if you wish with some tools to help refine.

Student Hardware Tools - 8pc Set this is a great set; it includes almost every shape and size to help you refine and detail your sculpt. There’s a comb looking tool in this set (XB) which can be used to scrape the surface, it will essentially rake the raised areas until level. To remove those scrape marks, I like to go back in again with another refining tool, ST3 HEAVY TOOLS Further smoothing the clay, ready for your detail layers!ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ

Smoothing your clay surface will create loose little clay scrolls, these are just the removed raised areas or rake marks! Brush these away and you can continue your sculpting.ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ

This process is going to be layer upon layer of refining, it may not sound like it’s useful, but the results will be effective!! Once this sculpt converts into your prosthetic material, the lumps and bumps of the surface will be very clear when it’s applied as the surrounding skin is going to be flat and smooth. Avoiding this is layers of refining.ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ

As soon as you’re happy with the surface, you can then begin to input your wound, scar, etc. design! Using the tools, you can carve into the clay. Using reference images throughout the sculpting process is essential – it will give you details to replicate to make it super realistic!ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ​​​​​​​ㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤㅤ

Following reference images can be a little gruesome, but great to use when creating realistic injuries!


You will see on all prosthetics there is a outer channel, surrounding the sculpt. This is something we call “flashing”. Flashing is something you also apply to the surface in clay.


When this is applied to the skin, the blending edge being so thin, is what gives you a seamless application. (The area on your flat surface - between the flashing and the sculpt is called the “blending edge”).

Using a small amount of rubbing alcohol (IPA or Acetone) you can melt this edge away from the flashing and it remain completely flush to your skin. This area, and the fact you previously blend your clay so smooth to the board, results in a perfect application!!


Essentially to create the channel, you can just roll out a long, even, thin sausage of clay and circle this around your sculpt, leaving a few cm distance between the sculpt and the flashing. Press this down onto the surface; you can then begin to neaten the channel.


Once you are happy with your sculpt, and the channel – you now want to move onto creating the walls around. This will circle everything, a few cm away from the channel which you will then fill with your moulding silicone.


PlatSil Gel 25 PlatSil Gel 25 Silicone Rubber is possibly one of our most versatile addition silicones; with  the use of additives, this silicone can be used for life casting, moulding and casting!!

PlatSil Gel 25 is a 25-shore silicone; this state would be too rigid to cast as a prosthetic appliance but a great shore for your flat moulds. An addition of PlatSil Deadener LV or Smiths Prosthetic Deadener when casting your prosthetic will bring the shore hardness down, depending on the percentage of your addition. Lowering the shore to around a 10, or even lower will resemble flesh exceptionally. So, with the use of one silicone, you have a mould and prosthetic pieces!

It’s a 1:1 ratio, exceptionally low viscosity and translucent; allowing you to pigment according to your design.


You can build walls by either using Buff Clay, you can hot glue tongue depressor/wooden sticks cut to size around the sculpt, you can even hollow out a plastic cup (if size permitting) and hot glue this to the surface. Gluing these to the surface will just prevent the fluid silicone seeping out)

If choosing to use buff clay (air-drying), you want to ensure the clay touching the board is secured to prevent the same as above – silicone seeping out. It’s not entirely essentially to get the clay super smooth; it won’t affect the moulds use as it’s the outer edge of the mould; it will however make a neater mould! Simply running a flat tool around the inside of the clay will smooth any lumps and bumps.

Now you have the walls built around your sculpt, it’s time to prepare your silicone to mould.

In two separate cups, measure out (by weight or volume) exact quantities of your part A and B. At this point, pigmenting your mould isn’t necessary but some prefer to have a bright colour so that it’s easy to see the casting silicone over the blending edge, etc. if you think this will help you, add a small drop of your chosen colour Silicone Pigments to part B.

When you’re ready, begin to mix these two parts together – the pigmented B part will allow you to see when the parts are fully combined as you will no longer see streaks of the clear/milky part A.

Bear in mind; PlatSil Gel 25 has only a 5-minute working time before it begins to thicken. The thicker the consistency, the likelier it is for you to entrap air bubbles in the mix. Gel 25 is a low enough viscosity for you to be able to use pouring techniques to avoid this; pouring from a height and allowing the flow to run super thin, pouring into one spot and allowing it to travel around the walls or vacuum degassing.

Once you’ve poured your silicone into the walls, give the silicone an hour before demoulding. By this time, it should have fully cured and isn’t leaving fingerprints when you touch test. Begin removing walls, and carefully peel back the silicone off the surface and clay. Begin removing any clay that has remained in the silicone and clean with a gentle brush of IPA.

You’re now ready to begin casting! Before you go straight back in with silicone, you’ll need layers of cap plastic, which we previously mentioned!


Super Baldiez diluted with IPA

Baldiez diluted with ACETONE


Brushing or airbrushing this solution = 6 parts IPA/ACETONE to 1-part Super Baldiez/Baldiez (6:1) in multiple, thin layers (making sure they’re dry in between each layer)

A way to test you have applied enough cap-plastic, grab a sewing needle, on the raised border outside of the flashing, pierce and lift the cap plastic, if you can lift the cap plastic and it’s not showing any holes – you have enough layers!


Once you’re done applying your cap plastic, you can begin preparing your casting silicone. This time you’ll be including softener, flesh pigments and flocking (if desired). In 3 separate cups, measure equal parts of A and B, you can add up to 100% of Part C (softener) to PlatSil Gel 25; this is up to 100% of your mixed A+B.



A: 50g

B: 50g

= 100g

C: 100% = 100g

= 200g (A/B + C)


Again, add silicone pigments and Flocking to Part B

Flocking are small fibres which when mixed into silicone with pigment break up the tone.


Mix all 3 parts together equally, and as before, pour from a height and in one spot to reduce air bubbles. Allow the mould to fill.


Using a wooden tongue depressor, scrape over the surface, flattening the silicone and allowing the excess to run off the mould. Here is where a pigmented mould helps: if there are any remaining trails of silicone that the tongue depressor missed, you can easily see where and wipe them away gently (not disturbing the cap plastic) with a cotton bud.


Allow an hour for a full cure and begin peeling out of the mould. Using translucent powder, brush this over the surface, and when you raise a corner from the mould, begin swiping the prosthetic away from the mould with the powder, taking away the tackiness.


Once your silicone has cured, you can go back in with cap plastic and sandwich the silicone. I personally like the tackiness of the silicone without cap plastic on the back. A little brush of IPA to remove the powder, along with your glue on application really helps with adhesion. It also prevents an overly thick blending edge. This is simply preference, you should definitely experiment to find what suits you best!


You now have a prosthetic appliance!!

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