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More Molding Tips
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Heidi Maiers
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Joined: 23 Feb 2005
Posts: 1223
Location: Near Portland OR

PostPosted: Tue Jul 08, 2008 4:01 pm    Post subject: More Molding Tips Reply with quote

Every time I make a mold I try to learn from the problems I have with the previous mold and try to think of solutions that solve those problems. Last time, I made the rubber and forton mold and then drilled the holes for the bolts before I unmolded it off of the clay original.

That worked ok, but problems were that it was very hard to drill through forton, and that it was very hard on the piece inside, cracking it to pieces. Also, it is not easy to drill through rubber and the holes left are very sloppy and torn looking.

In this case, I couldnít risk breaking the piece inside since the client wants the ceramic version fired and finished also, so I tried a different approach.
Normally, I would make the rubber mold in one piece with a seam down the back, and the shell mold in 2 pieces, but here I will make the rubber in two pieces and the shell in 4. Having an open mold allows you to paint in the first coat of whatever casting material you are using (wax, resin, etc) instead of rolling it, insuring even coverage and no trapped air pockets. Having the shell in 4 pieces allows me to remove it easily from the ceramic original and not risk breaking it by forcing off a tight shell.

After coating the whole thing with two thin layers of rubber (will later be cut open with a razor), I ran a fairly flexible wire around the perimeter of my seamline just to help keep the shim in place. I have had a heck of a time sometimes keeping the clay shim line to stay put while I apply the rubber.




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Heidi Maiers
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PostPosted: Tue Jul 08, 2008 4:02 pm    Post subject: Reply with quote

The wire kept the ceramic shim in place and I started building my layers. I placed some throw away brushes that were the right size for bolt holes through the shim and will mold around them. That worked well to make some nice clean holes through the rubber and after the rubber had cured, the brushes pulled right out and I trimmed the rubber back to the nub. I could have just as easily used some small sections of plastic or metal tubing, or even sticks of chalk.



I continued building the sections as usual and added a temporary shim (also with bolt holes on the front and back that will just act as a ridge of rubber that will fit between the two pieces of shell mold. This will anchor the mold and keep the soft rubber from flopping around on the inside when the mold is empty and possibly resulting in a distorted cast.


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Last edited by Heidi Maiers on Tue Jul 08, 2008 4:30 pm; edited 1 time in total
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Heidi Maiers
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PostPosted: Tue Jul 08, 2008 4:03 pm    Post subject: Reply with quote

Once the rubber mold is built up with about 5 layers of rubber, total, I let it cure overnight and then built the fiberglass sections.





I first put a thin layer of fiberglass (forton) on each section, but not on the ridges. This will give your next thick layer of forton something to hold on to. If you try to put a thick layer on the silicone, it will just slide off.


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Heidi Maiers
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PostPosted: Tue Jul 08, 2008 4:05 pm    Post subject: Reply with quote

When that has set for a couple of hours, I added a sheet of plastic wrap on each ridge to keep the sections separate.
Working each section, I build up the ridges and folded the plastic over the edge to smooth it down. Then I took a pencil and poked it through the rubber hole before the forton had set up, thus eliminating the need to drill through the forton later. Do this for all 4 sections and donít forget to keep your holes open.


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Heidi Maiers
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PostPosted: Tue Jul 08, 2008 4:06 pm    Post subject: Reply with quote

Let it set up overnight and unmold, cutting your seam open with a razor.
The ceramic came out completely undamaged, not even a scratch, and is now going through the drying process.


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Tamara



Joined: 20 Oct 2005
Posts: 952
Location: Northern California

PostPosted: Wed Jul 09, 2008 2:07 pm    Post subject: Reply with quote

Thanks Heidi! You have a way of explaining things so that they are easily understood. All your little tips and tricks are great. I like how you figured a way to not have to drill holes in the forton shell. Also, was interesting how although the shell has four parts, the rubber has only 2 parts. The extra rubber divider keeps it from slipping and distorting.

Thanks for all the pictures and time spent putting this together for us.

Smile
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Will Pettee



Joined: 24 Feb 2005
Posts: 130
Location: SF Bay Area, California

PostPosted: Wed Jul 09, 2008 2:38 pm    Post subject: Reply with quote

Wow -- Nicely done and a great tutorial to boot!
What a wonderful process.

Thank you Heidi!
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Mitch Mitton



Joined: 01 Nov 2007
Posts: 74
Location: Powder Springs GA

PostPosted: Wed Jul 09, 2008 4:58 pm    Post subject: Reply with quote

This is very interesting how you combine benfits of a soid cut mold with a multi part mold. Getting a good parting line off a dividerwall always leaves something to be desired. Very nice indeed. And as Tamara said holding the mold in place this way is really great.
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Heidi Maiers
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PostPosted: Thu Jul 10, 2008 3:47 pm    Post subject: Reply with quote

Hey, thanks!
Well, the mold worked pretty well. The only thing I'll do differently next time is to make the shim lines a little wider and place the bolt holes more towards the outside edge of the shim. Placing them in the center like this, by the time all the layers get added, they are pretty close to the mold on the outside and makes it awkward to get the bolts clamped down. Farther out and they can be sanded down flat and no obstructions for the wing nuts. On some of them, I just put the wing nut on one end and used a screwdriver to turn the bolt screw rather than being able to turn the wings with fingers.
Here's how the test cast turned out. Barely any seam lines to touch up.



Here is a photo of the original clay (fired) and two bronze copies made from the mold. This is just raw metal before the patina is applied.



You can view final bronze here:
http://www.heidimaiers.com/HTMGalleries/MargaretBronze.htm
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Last edited by Heidi Maiers on Sat Sep 13, 2008 10:16 pm; edited 3 times in total
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Chuck Williams



Joined: 26 May 2008
Posts: 56
Location: USA

PostPosted: Mon Jul 21, 2008 12:16 pm    Post subject: Reply with quote

Great stuff Heidi!

Thanks for sharing.

If you don't mind me asking, what brand of silicone are you using?
I'm looking for a good brushable silicone that will capture fine detail.

Also, what separator did you use between the front and back half of the silicone?
I'm assuming that after your first two thin coats of silicone,you built your clay wall and completed the front half of the rubber build up,removed the clay wall and completed the back half rubber build up.

I know what they say about "assuming", so feel free to correct me if I misunderstood your steps!

Thanks again!
Chuck...
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Heidi Maiers
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Joined: 23 Feb 2005
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Location: Near Portland OR

PostPosted: Mon Jul 21, 2008 3:51 pm    Post subject: Reply with quote

Hi Chuck,
I'm using the Smooth-On Mold Max shore 30 with ThiVex added to the brushable layers (after the second coat to thicken it up a bit).
As a separator, I'm just using liquid dishwashing soap (Dawn) and let it dry before applying the opposite side of rubber application.
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Heidi Maiers
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Chuck Williams



Joined: 26 May 2008
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Location: USA

PostPosted: Tue Jul 22, 2008 5:47 am    Post subject: Reply with quote

Thanks Heidi!

She really turned out great.
Enjoy that "Job well done, Happy client" feeling!

Chuck...
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Alison Belt



Joined: 19 Feb 2011
Posts: 200
Location: Baltimore, MD

PostPosted: Thu Oct 25, 2012 1:39 pm    Post subject: Reply with quote

Do you have to degass that variety of Mold Max? I've used oomoo in the past for that reason but it's so expensive and not as high a quality according to the people at Smooth-On. I've got a couple of flower reliefs just sitting....waiting...until I make up my mind about what to use on them.
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Heidi Maiers
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Joined: 23 Feb 2005
Posts: 1223
Location: Near Portland OR

PostPosted: Thu Oct 25, 2012 3:32 pm    Post subject: Reply with quote

Hi Alison,
I've never used a degasser. With this, right after I apply (on the first two layers only), I have a small air compressor standing by and blow the rubber to knock out all the bubbles while it is setting up. Don't blow too hard, or you'll blow the rubber right off the model. Just a wide, firm air flow does nicely. Always surprises me how many bubbles are lurking in there. After the thin bubble coats are on, I don't bother blowing the thicker layers that will follow.
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Heidi Maiers
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Jeanette Lewis



Joined: 13 Oct 2009
Posts: 595
Location: Merseyside U.K.

PostPosted: Fri Oct 26, 2012 12:06 pm    Post subject: Reply with quote

HI Heidi,
love the photo of the fired clay and bronzes, thanks for the tips!
Jeanette
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