Hi, I'm trying to make a stop-motion puppet out of silicone. I've sculpted my character from Chavant sulphur-free clay, can anyone suggest which plaster to make a mould from please? In my research I've seen a lot of ultracal and hydrocal names mentioned but they are not available in the UK, any suggestions please? 

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One brand I see at UK suppliers is Crystacal.  I just searched "hydrocal UK" and got a few hits.  Herculite Stone also appears to have a very hard surface.

Most hits turned out to be in the US, even when I put UK hydrocal UK to try and give it some priority.  Here's the one which actually is a UK supplier:  http://www.maragon.co.uk/arts-and-crafts.html#Init

A link to Semafor re-directs to Maragon.

I did better by searching for Crystacal UK:

http://www.specialplasters.co.uk/index.php?_a=product&product_i...

You should find a lot more suppliers pop up, since that is the brand actually sold there.

For silicone casting, you can also make a mould from fibreglass - either polyester resin or epoxy resin.  I've made two body moulds for casting silicone puppets from polyester resin, and they are strong, and much lighter and thinner than plaster needs to be.  But both had a slight tendency to warp, bowing out in the centre, so I put a spring clamp in the middle to squeeze it together when I put the halves together and pour the silicone to fill them.  I use Hydrostone or Ultracal for head moulds, both are available here in Australia, though twice the US price.

Hi Nat,
Don't bother with hydrocal or ultracal in the UK,we don't use it due to it's lack of availability.Crystacal R or Tiranti's Basic Alpha is what you're after. You don't say where in the uk you're located? Tiranti's have outlets in Theale near Reading and in Warren Street in London. Here's a link to the the basic Alpha:

http://www.tiranti.co.uk/EdgeImpactShop/subcatdivision.php?Division...

Any questions, ask away, as I'm based in London. :)
Thanks Nick and Maq,
I'm based in Rochester, not too far from London. Since I posted that question I've ordered some polyurethane casting resin, I saw this on some project posts online. Do you think that's a good move?
What are you planning to use the resin for?

I was looking in the paranorman 'art and making of' book and wondered what they use for making moulds, then I came across this blog and thought the results look great. That's what I ordered the resin for, to try instead of plaster. 

http://nathan-flynn.blogspot.co.uk/2011/04/mould-making-hands-feet....

Maq said:

What are you planning to use the resin for?
Ah, ok. I think they actually use an epoxy resin on those films but the fast cast route seems to work well for the Flynns.Ive never made a fast cast mould myself, only variations of plaster,silicone,fibreglass, urethane elastomer etc. Let us know how it works,strength,lack of air bubbles etc.Dont forget a good release agent between sides!
Ok, thanks for your help. I'll test it out and get back to you. If it doesn't work I'll try your plaster suggestion. Thanks again :)

I expect the resin is fairly expensive, have never used it myself. But looks good, and the mould prep in the blog is first-class. I assume it is used by the pros because it avoids the distortion issue with polyester or epoxy resins.

The plaster, or more correctly dental stone, I use is Crystacal R. The reason for using these high strength plasters is also because they are very dimensionally stable. But they still need some reinforcement to ensure the mould does not break. I use glass fibres or sacking. I have even used bits of string and chopped rope. Essentially long fibres that help to hold it together.

I have been using Dragon Skin for the final result, and it has been working very well. The mould lines can be a problem, and their fineness depends on how well you get the embedding water-clay against the sculpt. I have been using the hard Chavant NSP, and find that having a cold finished sculpt means that it is pretty hard, and therefore less likely to get scored.

After the first half is done, don't forget to add a little piece of clay at the side of the mould to give you a pry-space, for a screwdriver or similar. One each side if there is room.

For walls I have used all sorts of things over the years. The lazy way is to use some water-clay. Plastic damp-proof course (the black stuff that comes on rolls about 150mm wide) is good, also Duplo bricks. For these small moulds I collect yoghurt and houmous pots and cut the bottoms off them. Feet fit neatly into a yoghurt pot!

Release agent can be Vaseline. If it is warm, then it flows over more easily. Wax spray would be great, but I don't have the budget. Remember always that you must avoid any plaster-to-plaster undercuts. so while those little cubes in the blog look fine, there is always the risk of an undercut. I just use rounded blobs, which I make by indenting into the water-clay surround. Use several for a positive fit.

There is a very good comparison chart for plasters, working and settings times, strengths etc. in the catalogue for South West Industrial Plasters, who are in Dorset. http://industrialplasters.com/catalogue/SWIP/index.html They also stock moulding silicone, and have been a very good firm to deal with.

Hope this is helpful.

I looked at the blog, and I would agree about those blocks for keys. Although they are tapered, I would taper them a LOT more, so they are pyramids. Same with round ones, a hemisphere can still get tight around the equator, they should be less than half a sphere so there is still a definite slope around the edges.
I use water clay for the wall, except when I am making a polyester resin mould, because moisture stops polyester from setting. For those, I used Klean Clay, which is very soft and not much good for sculpting details with. It helps that it is softer than the Chavant Medium NSP I aculpted the figure out of.

One little tip, apologies if it is blindingly obvious:

When mixing plaster, the way I usually get the quantities right is to put water into my mixing container to about 1/3rd the volume of the plaster I need. Then I add plaster, enough to make an island. Then I mix. It should come out like thick custard. Don't be tempted to add the plaster a little at a time - you may end up with it starting to set before you get the consistency right!

You can brush the first layer of plaster into the mould, or pour some in and blow hard. The idea is to get rid of any air pockets and fill the surface completely. Often the vaseline release makes the plaster bead up and you can't get that last little air bubble out. In that case it is possible to add a tiny drop of washing-up liquid to the first plaster pour (I usually put a drop on the brush), and this will let it flow.

Oh, that's two tips! 

Hey Simon,

Thanks for those two little tips :)

Very useful, thank you


Simon Tytherleigh said:

One little tip, apologies if it is blindingly obvious:

When mixing plaster, the way I usually get the quantities right is to put water into my mixing container to about 1/3rd the volume of the plaster I need. Then I add plaster, enough to make an island. Then I mix. It should come out like thick custard. Don't be tempted to add the plaster a little at a time - you may end up with it starting to set before you get the consistency right!

You can brush the first layer of plaster into the mould, or pour some in and blow hard. The idea is to get rid of any air pockets and fill the surface completely. Often the vaseline release makes the plaster bead up and you can't get that last little air bubble out. In that case it is possible to add a tiny drop of washing-up liquid to the first plaster pour (I usually put a drop on the brush), and this will let it flow.

Oh, that's two tips! 

And one more just for luck: Don't try adding water to dry plaster - all you'll end up with is a lot of lumps!

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