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Author Topic: Sculpting larger forms  (Read 333 times)

Offline OSHIROmodels

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Sculpting larger forms
« on: June 04, 2018, 10:16:58 AM »
I'm going to be sculpting some larger 'things' in the near future and was wondering what peoples preferred substrate was. I've heard that tinfoil can be used but that seems a bit unstable to me. The 'things' I'll be sculpting will be an inch or two long and will be fairly substantial.

cheers

James

Offline beefcake

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Re: Sculpting larger forms
« Reply #1 on: June 04, 2018, 10:21:08 AM »
Tinfoil is useless if it goes into vulcanisation as the pressure affects it I believe. I use either airdrying clay for something very large and sculpt over that (not sure how that would work being cast) or Milliput which is fairly cheap over a rather thick wire armature. Then again, sculpt over the milliput.

Offline OSHIROmodels

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Re: Sculpting larger forms
« Reply #2 on: June 04, 2018, 10:26:29 AM »
Thanks :)

Should have said that these probably aren't being metal cast and would only need to withstand rtv silicon.

Air drying clay sounds like a solution though.

Offline beefcake

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Re: Sculpting larger forms
« Reply #3 on: June 04, 2018, 10:33:01 AM »
I figured it probably wasn't as you said they were large.  :)

Offline OSHIROmodels

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Re: Sculpting larger forms
« Reply #4 on: June 04, 2018, 10:37:32 AM »
Still useful to know though  :)

Offline tin shed gamer

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Re: Sculpting larger forms
« Reply #5 on: June 04, 2018, 10:52:12 AM »
James,

It really depends on what your making and how big.

I'd always use a wire frame then add a layer of adhesive and then a clay then another layer of adhesive.

Air drying clay will stress fracture can only be built up in stages which causes weak joints.

My go to strengthening agent is J.B weld. A two part epoxy adhesive there's a couple of versions a five hour and a twenty four hour(even stronger than the five hour.)It can be filed and sanded.
It's often used to attach scope rails to firearms. It's seriously tough stuff.



Offline ink the troll

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Re: Sculpting larger forms
« Reply #6 on: June 04, 2018, 02:35:26 PM »
Tin/ aluminium foil will work for stuff that is just one off models or things that won't have to put up with vulcanisation or lots of pressure. It's more or less regularly used for making larger scale garage kits, masks, props etc. especially when using non-drying modelling clay (and polymer clay). There's even people building entire models out of foil.

While foil can be used without a wire armature (and not using a wire armature has some merrits*), generally for bigish models you first build a wire armature and then tightly wrap that in foil. Tightly as in 'no air pockets'- important when using eg polymer clay that'll be cured in an oven, as trapped air will try to find a way out and can cause cracks in a sculpt.
Usually you'd then build up the basic shape with more foil and more wire that you tightly wrap around the foil for more strength. Last 'layer' of that wire foil cake usually is wire, as that helps to not only strengthen the armature but also will provide your sculpting material of choice with something that is easier to stick to than bare foil. A little trick for better adhesion is to use crumpled foil.
Once you've reached a point where you're happy with the general shape/ thickness/ strength of your foil bulked armature, you start adding putty/ clay/ paper mache/ plaster wraps/ whatever.

Personally I've never had any problems with polymer clays, milliput or greenstuff (or a mix of any two of those) not sticking to simple household aluminium foil.
Air drying clays can be a bit tricky as most of them will shrink to an at least somewhat visible extent and that can leave visible 'seams' where the clay kind of lifts off the underlying surface, the surface can also fracture while drying (a bit like a dried out river bed will crack). For larger pieces they generally work better on/ over an absorbent core (eg a paper mache hill clad in clay).  Though you could always combine that with the foil/ wire (foil/wire -> paper mache ->clay).
One thing to keep in mind is that air drying clay is heavy- if you're going down that route, have a look at those 'super light' air drying clays as well. While I found the light ones I used anoying to work with (a bit like trying to sculpt something with icing), they're still usefull for adding more bulk to the armature and generally can be sculpted over with more hard wearing/ easier to work with materials.

My advice would be: buy some air drying clay, a package of the 'super light' stuff, and experiment a bit before you start on the real thing.
I've sculpted over styrofoam, cork, aluminium foil, action figures, plastic eggs and various putties with air drying clay and so far it hasn't fallen off. I actually just tested standing on one foot on a terrain piece and it didn't succumb to my weight, so pretty solid if you don't use it for delicate structures.


*If no wire is used and you're using a sculpting material that hardens enough, then you can pull out the foil later for creating a partially hollow model.
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Offline OSHIROmodels

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Re: Sculpting larger forms
« Reply #7 on: June 04, 2018, 04:53:17 PM »
Many thanks gents, most useful  :)

Offline snitcythedog

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Re: Sculpting larger forms
« Reply #8 on: June 04, 2018, 06:00:56 PM »
I have used tinfoil in the past to bulk out larger models.  If you use the tinfoil compress and shape it into a tight ball and attach it to your armature.    Then you can put a substrate of air dry clay or sculpy over the surface to give a uniform surface.  Just be sure to leave some gaps in the surface of the putty so any air can vent out if you are heating it up.  As noted not for vulcanization but since you have said it is for RTV you should be fine.  My two cents and I hope it helps.
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Offline ink the troll

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Re: Sculpting larger forms
« Reply #9 on: June 05, 2018, 02:42:14 PM »
One thing about air drying clays that nobody mentioned, is that they usually aren't waterproof and have a somewhat porous surface after having fully dried. So it's probably a good idea to seal the sculpted object prior to moulding it.

I did take some pics of stuff made with air dry clay. Hope they show up, using google photos for hosting is not all that great.

the most extreme example of clay lifting off a surface I have encountered so far (and mostly down to me not properly blending the rock surface into the floor):


most of the surfaces were made from clay and the 'seams' are far less visible (if at all) on the rest:


the proof that air dry clay will stick to styrofoam/ XPS:


Green stuff, neat and mixed with Milliput over air drying clay (the white and terracotta coloured material):


Clay over Greenstuff, Milliput, Milliput mixed with Fimo and/ or Greenstuff and what little bits of action figure hadn't been covered with epoxy putty: