Silicone 101

How to make a case mold.

 

Believe it or not some of the most frequent questions that I get about silicone are not about making appliances, or using it as a casting material, but rather there are lots of people out there that just want to know how to use the stuff to make a simple mold.

So... ask and you shall receive!

 

Now a disclaimer... The materials and techniques in this article are given in good faith. Replicants.org, and aRvin Clay will take no responsibility and assume no liability should you try this at home.

Also. This is just one way to do it. I'm certain three are other ways to go about making molds and such so feel free to experiment an stuff. Should you have any questions feel free to send an email my way.

 
 

Here's our model. Its a stone head cast with latex baldcap, and silicone goggles.

 

 

 Now because of the strange little undercuts on the goggles we had to do a bit of filling in and such.

 
 

 Here you can see the corrected areas in blue where it was filled with Klean Klay.

 
 

To add a little bit of stability to the model I built a crayon sized support in epoxy.

 

 

Now the next step before making your "core" is to cover and protect your model. In this case I used a bit of plastic wrap. This will save you lots of time in the end.(There is nothing more unexciting then cleaning wet clay from a model)

 
Here I am finishing up the laying up of clay. I built an even thickness of 1/4 of an inch all around the model.
This is a shot of the back of the clay. Note the ridge that I built up. This section is where the finished silicone will be split to remove the model (and eventually the castings)
The front of the clay. The little nubs are the pour spouts. This is where you will eventually pour your silicone into the case.
Dividing wall added. Now I need to back track a bit here. I cannot stress enough how important it is for you to make sure that the cal you add, and the dividing walls are as neat as possible. Its just a good idea to get into the habit of doing this. Your presentations will look better in the end. 'Nuff said. :)

Side view of the wall.
Back of the clay wall, just before I cleaned it up, of course.
Now that my walls are finished and I have coated the clay with lots of Crystal Clear, and Universal mold release I'm ready to begin making my jacket. I opted to use Smooth-on's Plasti Paste. In its uncured state its base ( or part b) is a white fibrous stuff that looks a bit like mom's mashed potatoes, only more toxic. Heh. It has a working time of about 8-10 minutes and builds up really fast, so its ideal for a quick case mold. Because its a resin be SURE to wear protection, you don't want to breath in the stuff, or get it on your hands. (I'm still picking off bits of it a few days later) Its mixed in a 1:3 ratio (1 a to 3 b)

About 3/4 of the front of the mold is now covered. This took me about 5 minutes to do.
Side view of the completed front half.
The right half completed
And the left half just prior to its completion.
And the completed left half. Now we give that sucker overnight to completely set up and the next morning we are ready to pull it apart
The next day I came in and after a cup of coffee, pulled the front half off. The pile of clay next to the model is everything that I pulled out of the negative mold.
Front of the mold just before I spiffed it up a bit. If you note the area that looks a bit uneven... I had the material a bit too thin there and it snapped off. Oops. Be sure to take care in applying an even amount of material all over your model. :)
Once both halves of the mold were cleaned of waterbased clay I drilled several holes around the 3 parts to bolt the halves together, and some vent holes around the mold. The purpose of these vents is to give you an idea of how much your mold is filled with silicone. As the holes begin to leak silicone you plug them up with oil based clay. This is a picture of the molds, all boltylike just before we begin pouring the silicone.

Here is a shot of the ultra high-tech device that was built to facilitate pouring the silicone into the case.
Here is some freak with weird hair pouring silicone into the mold. For the negative mold I used gi1000 from silicones Inc. I like the stuff. It has a 10:1 ratio and allows for some amount of leeway with the proportions.
As your mold begins to fill you are going to need to start filling in the vent holes.This shows the bottom of the mold with clay keeping the silicone in
Here is a shot from above. The silicone is just about to the top of the first pour spot. Soon we will plug this up and begin using the top spout.

Pour spout plugged. From this point on I used the top spout to fill the mold. It only took about 3 quarts to fill the mold.

Now in about 24 hours I'll be able to pull everything apart...