A few basic questions about casting in platinum silicone

Hello all,

I'm just getting started with casting molds after experimenting with rubber latex for a little while. I still have a couple of things to pick up at the art supply store, but I plan in the coming days to experiment with casting a character's body with Smooth-On's Rebound 25/40 platinum silicone. I hoped to ask a few lingering questions about this process first, as while I'm well aware of the role mistakes play in the overall learning process, it would be pretty nice to end up with a usable puppet body on the first try and save on that expensive silicone :)

About the character:

 - It has no mouth or nose, just two huge eyes sitting on top of a neckless torso, so all that's being molded here is a simple, cartoony body with no feet, hands or anything above the collarbone (since those are separate components)
- Roughly 7 inches tall

My questions:
1. The silicone I'm working with is awfully thick and viscous - how can I thin it out a bit to reduce the chance of air bubbles without reducing the quality of the curing?

2. I want my character to have a solid, apple-red skin color - is it better to add paint while mixing the silicone components, or paint onto an already-cured surface? For either scenario, which type of paint is best? The silicone I'm using has a default pink-orange tint, if I wanted it to be, say, white or green, is there anything I can do besides buy a different brand?

3. Is any brand of plaster of paris suitable for making the mold itself, or should I only buy a particular brand or quality level? Is vaseline sufficient for separating the halves of the mold or should I invest in another material for this?

Much obliged in advance for any guidance - I'll be happy to post progress pics for anyone interested.

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I've done several heads, and a couple of bodies, in platinum cure silicone.  I need to look up the Rebound 25/40, I don't know that one -

Ok, got it.  It is meant to be thick, so you can spatula it onto a vertical surface and it will stay there.  It is made for making moulds, not for casting puppets or makeup prostheses.  It comes in a shore A hardness of 25 or 40 - that is usually too firm for a puppet body.

Question 1:  I had been using Polytek's Platsil Gel-10, which is Shore A hardness of 10, a lot softer.  I still use it to paint a surface skin on, but it doesn't pour as well as Smooth-On's Ecoflex 00-30.  The 00 is a different scale, so it's actually softer than a Shore 10 silicone.  That really helps for a body, especially if it is not skinny.   Smooth-On also make Dragonskin, with a Shore 10 hardness, but I like softer than that.   So I would suggest you don't use the Rebound.  Also it has a colour already, the silicones made for casting puppets are clear and can be tinted to any colour.

I tried a "silicone diluent" for thinning my Platsil so I could pour it in better, but it seems to be a silicone oil, and although the silicone cast cured ok, it kept sweating oil for a week.  That was despite not using it on the skin coats, it came right through, and I scrapped that cast and re-did it in the end.  There is also Smith's Theatrical Deadener or Smooth-On's equivalent, intended not so much to make the silicone runnier to pour, but a bit softer, but it also means it stays a bit sticky.  So you can pour it on the inside if you painted a few layers of skin on the mould first without any of the deadener in it, but you don't want it on the surface.  Using the Ecoflex 00-30 without deadener was softer anyway, with no tackiness problem.

By painting a skin on, you brush out any air bubbles, and if a few tiny bubbles are in the stuff you poured inside, it isn't a problem anyway.

Question 2:  It is best to tint the silicone to a good base colour to start with, and only do surface painting to add subtle shading.  I use the Silc-Pig pigments made for mixing into silicone to colour it:   http://www.sculpt.com/catalog_98/moldingaccessories/pigments/silico...

I got one each of red, yellow, blue, white, and black, which lets me mix any colour - though so far it's always been flesh tone.  I put enough of the silicone part B into a separate container to cast the puppet (with the addition of an equal amount of Part A) and mix the pigment into the Part B.  Then I can mix up small amounts for painting the skin, and later a bigger amount for filling the mould, and it will be the same colour.  They also have fleshtone kits I think.  The red will last forever, a tiny amount goes a long way, compared to other colours.

The only thing that you can paint silicone with is more silicone, so you will be mixing up small amounts of the same silicone, with pigments in, to paint the surface.  You can thin with Naptha. Some people have reported success with adding small amounts of oil paint, or acrylic paint, to the silicone, but I haven't wanted to risk it.  Test it before you paint it on the puppet, make sure it cures with the paint in it.

Question 3:  I use Hydrostone or Ultracal 30 for making the plaster moulds.  Or at least, for the first couple of coats, to get a good fine hard surface.  I often mix it with cheaper casting plaster to make the outer layers, with some chopped strand fibreglass matting or hessian (Burlap in the US) to reinforce it.  Ultracal is the one most often recommended for professional work.

Here is a video showing the process I go through for making something small - a puppet head - in silicone.

Hey Nick,

You are a treasure - thank you so much for the advice and guidance. I've been a longtime fan of your youtube videos (especially the silicone puppet head one) in preparation, and I'm excited to experiment with this myself and gain some experience-based knowledge. 

Cheers again!

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