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Unread 06-13-2013, 10:37 PM   #1
Tomecko
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Help with 2-part molds for resin casting!

Yo! I've been trying to make two-part silicone molds for casting small gems and jewelry parts, but apparently I'm not using the right sort of silicone-to-silicone release, because for the second time, I have sealed my model inside a silicone tomb.
The first attempt, I used my Castin' Craft Mold Release, which apparently wasn't strong enough.
The second attempt, I used the Smooth-On's recommendation, Ease Release 200. And still my mold sticks together!
Anyone know what I'm doing wrong? Is there a better release meant specifically for silicone-to-silicone?
For reference, I'm using Smooth-On's MoldStar 16 silicone mold mix.
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Unread 06-14-2013, 08:20 AM   #2
verdatum
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One common practice is to just pour the mold as a single piece, and then slice it into 2 pieces to unmold it. You cut along the edge using an x-acto knife or scalpel, using a very pronounced zig-zag pattern so that the mold will lock back together when reassembled.

For many shapes, you don't even need to split the mold all the way. You just split it enough to peel the mold off of the prototype. This works particularly well when making brush-on "glove" molds.

As far as releasing silicone from silicone, the ease release 200 should work. It is possible that you haven't applied enough (not that it really takes all that much), or that you are just being a bit shy in separating the mold. Mold silicone resists tearing pretty well, so you should be able to tug at it quite a bit to make your mold split.

I might be able to give you some more tips if you post photos of your molds.
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Unread 06-17-2013, 04:27 PM   #3
Tomecko
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After slicing my mold apart, I have concluded that I did not apply enough Ease Release - a couple of my registration keys survived, and at a few points, the mold did want to separate along the line. Perhaps it's because it's a brand new can - I thought the mist was coming out awfully fine, so I even applied it twice. I'll just have to absolutely douse it next time.
I do like the zigzag slice idea, too!
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Unread 06-17-2013, 07:09 PM   #4
astillar
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Instead of Ease Release, I use the Sonite Wax when casting silicone against silicone.
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Unread 06-17-2013, 07:16 PM   #5
verdatum
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One trick is after spraying the release, to brush along the silicone with a soft flat artist's brush. This smooths out the release agent into a solid film, in case it was merely sputtered on in droplets. I use something like a bit of tape to mark brushes like this, since they aren't any good for painting after this. Silicone oil causes all sorts of flaws in many types of paint. Washing the silicone oil off requires powerful solvents, so I just don't bother.
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