I need to shrink something

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hez1

New Member
So I've been charged with a fairly tricky task, and would like to get some opinions on how I might go about it. My friend has a Battlestar Galactica (new series, not the original) pilots helmet, the only problem with it is that the sculptor got the scale wrong, and it's between 15-20% too large. He would like me to fix that, without having to resculpt it.

After exhausting a couple of avenues, I've come up with a somewhat arduous process that I think could work, but I'm not especially familiar with some of the materials, and would like some advice. Here's how it would go:
1) mold the original.
2) do a clay pour into the new mold.
3) make a 2 part ultracal mold of the clay pour.
4) Pour latex into the ultracal mold.

Step 4 is the one that I'm least certain about. I'm not sure how much latex shrinks (I've heard of people making their pred sculpts about an inch too large to compensate for shrinkage), and I don't know if the shrinkage increases or decreases when the thickness of the casting increases. Obviously I would need to make this fairly thick, and then probably foam fill it with at least a 10lb foam to support it.

If this wouldn't give me the amount of shrinkage needed, then I may need to repeat the process. Which brings me to...how much detail would I lose by casting with latex? Obviously a helmet doesn't have anywhere near the amount of natural texture of a pred head, but it's worth considering.

Thanks in advance for anyone who may be able to help out.
 

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Yarko

Well-Known Member
There are certain types of clay which shrink when you bake them at high temperatures. They are used for pottery (ceramics). You could mould the original, make a clay pour, then bake the clay (you need a special oven or kiln for this) and then you mould the shrunk piece and make a new resin casting.
 

ptgreek

Active Member
There are certain types of clay which shrink when you bake them at high temperatures. They are used for pottery (ceramics). You could mould the original, make a clay pour, then bake the clay (you need a special oven or kiln for this) and then you mould the shrunk piece and make a new resin casting.

But will the whole sculpt shrink to the exact proportions as the original?

Latex can shrink up to 12% when fully cured ..but that is also not an exact figure ..it should however capture the details just fine
 

Yarko

Well-Known Member
It will shrink to the exact proportions. Depending on the clay you use, it could shrink up to a 30%. Some clays shrink more than others, but you'd have to ask a potter (not harry) for accurate information
 

hez1

New Member
That clay sounds like it would be perfect, but I'll have to look around for someone in the area that does pottery work.

George, with the latex, something is worrying me. It may not be an issue, but I've never done any latex work and am trying to see all possible problems. I pour the latex, and let it sit for a few hours...the pour it back out and see how thick of a skin it has formed...when it shrinks, does it pull away from the mold? Would pouring foam in at this point potentially affect the cast (i.e. warp it at all)?
 

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ptgreek

Active Member
That clay sounds like it would be perfect, but I'll have to look around for someone in the area that does pottery work.

George, with the latex, something is worrying me. It may not be an issue, but I've never done any latex work and am trying to see all possible problems. I pour the latex, and let it sit for a few hours...the pour it back out and see how thick of a skin it has formed...when it shrinks, does it pull away from the mold? Would pouring foam in at this point potentially affect the cast (i.e. warp it at all)?

Honestly Bro ..I just dont think that making a latex mold is gonna shrink it enough for you. Accidentally, we left a hot clay pour in an alginate mold with plaster jacket for far too long..it was a life cast ...the alginate pulled away from the jacket and really shrank the clay casting up, but I really dont think that it shrank constistanly. The problem is that you are doing a helmet ..something that needs to stay in the exact same proportions all the way around...if there is a variance anywhere, it will looked warped ..thats why the clay in the kiln idea worries me. there is no way for the clay to "know" that it has to shrink exactly the same in every spot.
 

hez1

New Member
I did think about alginate, but yeah, the inconsistent shrinkage seems like it would be too much of an issue. And I don't want to make a latex mold, I want to make a latex cast of the helmet. That way it seems like the shrinkage would be fairly consistent (again, not cast with latex before, so have no experience to draw on). How the foam would affect it in the mold is something I'm unsure about too. If the shrinkage isn't enough, then I can go through it all again, and end up with a second latex cast. At that point I would probably stop whether the shrinkage was enough or not, because the chance for slight warping to increase just gets worse with each cast made.
 

MEANGENE83

Sr Member
I dont remember exactly where I saw the product. But i remember coming across some specialty material made for this purpose. It wasnt dragon skin but for some reason I wanna call it that. Maybe it was made by the same company.

My gut is telling me is was made by a smooth-on type of company.

There is something specifically made to shrink items in this way. But for the life of me I cannot remember the name.

If you start scowering manufacturers websites I will do the same and together we will come up with the answer.



The latex route you are thinking about isnt the best way. Latex doesnt hold detail as nice as the helmet probably is now. It just wont look as nice.
 

Tonkers D

New Member
one of the purposes of alginate is for size reduction. I live extremely close to a place called silpak, and i have seen reduced parts that look excellent. From what they have told me and what i understand, you make a mold of the part in alginate, and then demold your part. after letting it set for a while, it will begin to shrink. (DUH YOU KNOW THIS :) ) To make it shrink evenly i would suggest some sort of block mold. it would have to be one piece. OR you could do a injection bladder mold, by creating a thickness over your piece in wed clay, making the jacket, then removing the wed clay, and then injecting the alginate into the void. that would keep a consistent thickness.

I have used alginate from silpak personally, and this really shrinks a ton. eventually it gets hard and cracks, but for a while (first hour or so) it reduces semi evenly even for a variating thickness lifecast.

Theres some more info here:
http://www.silpak.com/lifecasting/61-life-...ginate-alginate

Hope this helps,

Derek
 

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hez1

New Member
Thanks for all the suggestions guys. In the end, we abandoned the idea. Turns out the helmet in question was really just sculpted out of proportion, rather than simply too large. So I need to go a different way on it, which will be easier. Hopefully.
 

Eaglewood

Sr Member
3D laserscan and 3d printing. It will be exact in every detail and to perfect scale. Let me know if you need directon for this.
 

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