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Unread 01-29-2013, 02:56 AM   #1
Nostrum
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Rub'n'Buff on latex? AKA- How to create a metallic look to latex?

I'm working on a costume that has armour, seen here.
I've decided to make it out of latex, reinforcing the front and back sections whilst leaving the area just below the arms softer for comfort's sake.

My question is about giving it a metallic finish so that it's closer to resembling armour.
I'm planning on tinting the latex first, to give it a base colour.
Will Rub'n'Buff work on latex? Or is there a better option to create the finish?

Am I going in the completely wrong direction?
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Unread 01-29-2013, 08:58 AM   #2
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I honestly don't know if rubnbuff works for latex, test maybe? Is it going to be molded latex, coated form, or making a sheet and cutting it to shape? Because the finish will actually be different with different methods
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Unread 01-29-2013, 01:28 PM   #3
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Rub-n-buff is oil based, so it will weaken latex a bit.

Instead, you can take advantage of latex's tacky nature. As you unmold the piece, or after the final layer of latex has dried (depending on your technique), brush the surface down with metal powder (aluminum, brass, bronze, gun metal, whatever is appropriate). The entire surface will pick up a nice even coating. Buff it very lightly with a soft cloth and it will take a shine. Metal powders can be obtained from your local hobby shop. Wear a good quality dust mask while you use it.

If you are molding the pieces, you can also brush a thin layer of metal powder onto the mold before the latex is applied. The powder will generally stay more or less in place due to static electricity. It'll serve as a release agent, and help it to pick up a nice even layer.
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Unread 01-29-2013, 07:51 PM   #4
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Brilliant, thanks Verdatum.

I'm going to make an oil clay sculpt and then a mould from plaster, and then latex cast from that.

We've got aluminium powder from resin casting, that'd work wouldn't it. Would it be a bad idea to mix it into the first layer of latex too?
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Unread 01-29-2013, 08:43 PM   #5
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Yeah, that's the stuff.

When you mix the powder into the latex (or resin, or whatever,) it has a strong dulling effect. Aluminum just kinda comes off as grey. On resin, this is ok, because you can buff down a layer revealing the raw metal; but you can't buff latex, so there's not much point. Plus when casting latex into plaster, you want to slushcast the first layer, and if you add aluminum powder, it will thicken it reducing its ability to slush about. Just tint the latex a good solid black. (Some people use a brick red behind brass or gold).

I find the whole layering process too tedious when working with latex. It takes layer after layer to get anything thicker than a Halloween mask. For a bit more money, you can go with a nice thixotropic polyurethane rubber and do the thing in one batch. It's much more adhesive than latex, so with plaster, you want to brush the mold down with a couple coats of alcote (aka liquid foil). Then after the polyurethane has fully cured, you can just dunk the plaster mold in a tub of warm water for awhile, the alcote dissolves, and the casting just floats right off.
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Unread 01-29-2013, 09:50 PM   #6
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I just realised I didn't link to the reference in my last post like I intended to. So here.

So I'm not going to be obsessive about a shiny metallic finish due to the amount of weathering that will be going into it.

Will rub'n'buff weaken the latex significantly? Would it affect the actual finish?
Will aluminium powder only give a dull finish? Not that it really matters, but is there something to top coat it with to give it more of a shine? Something like Liquitex Matte or Perma-wet gloss?

Is it all going to be a matter of many trials and errors?
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Unread 01-30-2013, 12:25 PM   #7
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If you brush the powder onto the mold, it gives a nice realistic shiny metallic finish. here's an example of the process: http://www.youtube.com/watch?v=biYUuA100EE This one is using the "gun metal" powder. The "silver" powder (which is actually aluminum) is brighter.

Paradoxically, clearcoats tend to reduce the metallic effect; they make it look more artificial.

I can't say how much Rub'n'Buff weakens the latex. I'd do a test, but I think my latex is expired. If dead set on using rub'n'buff, and it does have a significant effect, you might be able to protect the latex by first rubbing in a thin layer of castor oil. You can get castor oil at your local pharmacy. If they don't have it in stock, they can usually order it and have it in one business day.
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Unread 02-01-2013, 07:51 AM   #8
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Picking your brain again, the next hurdle I'm coming to is the metal powder in the plaster cast. Some reading suggests I should use wax (which that same channel does here).
I'm sure with the right release the metal powder would bond to the latex (or, I'm starting to lean much more toward urethane), but I have casting silicone which I'm not keen to use for such a temporary project. Ignoring that, might it be a better option to coat a thin layer inside the plaster mould (Or, a silicone layer over the clay before plastering) since all signs point to metal powder definitely not sticking to a silicone mould?
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Unread 02-01-2013, 04:55 PM   #9
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So if you use latex with plaster, the idea is that you want the plaster to actually absorb the water in the latex, allowing it to form a nice skin. If you use polyurethane, the stuff is super sticky, so you need a well-released waxy surface to facilitate pulling the mold away.

Latex doesn't work too terribly well in a silicone mold, because latex needs a way for the water to leave the rubber for it to cure. So if you go with a silicone mold, you should probably cast with polyurethane.

Making a silicone brush-on mold with a plaster mother-mold is a great way to save on silicone costs. You just need to make sure the silicone you use is thixotropic, which is a fancy word meaning it stays put wherever you brush it. You can make a regular silicone thixotropic either by adding special silicone thickening agents, or by mixing in colloidal silica (cabosil). But silica is sorta nasty stuff. Wear gloves and a good dust mask and mix it thoroughly in small batches until it has a consistency slightly thinner than mayonnaise. And do this before mixing part A and part B, in equal proportions to both parts. Brush-on silicones also usually have a quick cure time; under an hour or so. Brush the silicone onto the clay sculpt, not to the inside of a plaster mold.

Metal powder will properly cling to the inside of a silicone mold. It should cling to a plaster mold too. If it doesn't, mix up some dishsoap with a touch of water and brush it on to the inside of the mold before applying the metal powder.
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