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Wednesday, October 22, 2014

Silicon Mold Making for Anyone

Last night I made molds in preparation for a planned visit to Tech Shop Pittsburgh. If you're not familiar with Tech Shop, I described it and everything I was learning to do there on my art blog last year. The molds are bell shapes that I plan to vacuum form poly carbonate sheets onto to reproduce many clear, plastic bells for Christmas Ornaments I am making. It sounds complicated, but it's really not once you break down the steps. There will be more on the details of that project in a later post.


Right now I just want to share the process of plaster casting using a home made silicon mold. It's actually surprisingly easy and, I think, very cool.
First, I had to choose the items I wanted to duplicate. I chose bell shapes because they will work well with vacuum forming. I'll explain why that is in the later post I mentioned. I was able to locate some bell shapes that I liked. One was a bell my friend Anna's mom got when touring Europe... aka an irreplaceable brass relic, and the most delicate and important item in my possession that week.

The other bell I chose was a plastic, bell shaped Christmas ornament that apparently has been in my family since my mom was a child. I know this because when I asked if it was okay to destroy it by cutting off the top attachment, my mom said "Oh, I remember that on the tree when I was a child." The consensus was "destroy it." We Sternbys are a sentimental lot.

Next step was prepping an outer shape for my mold. I tried to find the smallest outer shape possible for the mold so I wouldn't waste as much silicon. That shit ain't cheap. Below you can see I glued the bell with silicon glue (easy to peel off of anything) to a sheet of watercolor paper (firm enough to withstand some water contact, but still disintegrates when soaked in water). Then I glued the outer shape around the item. Rocket science.


Next comes my least favorite part, which is eyeing up equal parts A and B silicon stuff. I seriously hate this part because I am too lazy to find a scale, and I am awful at estimating volume. Another pain (seriously, why do I do these things) is stirring the mixture so the reactive stuff at the bottom of the pink stuff is all mixed in.


Don't let any of it get on your clothes, obviously, but really try not to get it on your hands. Surprise, silicon is very water repellent. I would go as far as to say it is hydrophobic but I do not know the requirements of that property, nor do I care. It's freakin' hydrophobic.


Pink + White = Still Pink


So you mix them together reeeeally well in a container hopefully with a spout. The spout is very helpful. I suggest you use your mom's measuring cup. 

Mom: "Tori why is there wax in my measuring cup? It's been through the dishwasher twice." 
Me: "It's not wax, it's silicon."
Mom: "..."

Anyway, for real use a measuring cup, and hopefully it's a glass one with a spout. And I will say something VERY IMPORTANT: when you are done with your measuring cup do not, under any circumstance, put water in the measuring cup or attempt to was the pink stuff out. Just let it dry and peel it off later. You will seriously be so much better off.

Once your silicon is all mixed up, you will need to pour it into the container surrounding the item you're molding. The only way you can screw up at this point is if air bubbles get trapped. If your shape is relatively simple, like my bells here, there isn't a high risk of bubbles. If you have a complicated item, there are a few things you can do to try to avoid the bubbles. 1) use a brush or a spoon to slather some of the silicon mixture onto the surface of your item, then pour or 2) pour your mixture in and poke a utensil into the silicon to try to jostle any bubbles that have formed on your item. I should probably mention that I've never actually tried either of these suggestions, but I think they're both sound options.

Regardless of any prep you choose to do, you'll definitely want to follow the next steps. 1) when you're ready to pour, tilt the container you are pouring INTO at about a 45 degree angle and slowly pour the mixture down the side of the cup like if you were pouring beer into a cup and trying to avoid foam. As it fills you can begin to turn the container upright, OBVIOUSLY. 2) slap the shit out of your container after to try to shake out any bubbles. Slap the sides, slap the bottom. Put it on top of a shaky dryer. If you have a vibratory rock polisher from a rock polishing phase hold it on top of that and let it run. Whatever you can do to get those bubbles to the surface, do it. 3) WALK AWAY. Set that baby on a very level surface and don't touch it again till the next morning. I mean it. Don't even touch it to check on progress. The silicon won't cure any faster than it should just this one time. I promise. The cure time for your mold will be listed on the box of whatever kind of kit you get. I think mine was about 8 hours. Anyway, overnight should do for good measure.


So finally, when you wake up you can go check on your molds and they'll be all set, literally. Give the container a little squeeze to be sure it's solid or touch lightly with your finger. If it's not solid a few hours after curing time, your mixture quantities were off. Now you should be able to remove the paper. My preferred way is to rip it partially but just to be safe I remove most of it by saturating it with water and allowing the paper to disintegrate. Once you clear away the paper that was obstructing the object within, you can start to pull the mold away from the sides. Don't be too worried about breaking the mold at this point. as long as no sides are thinner than a quarter inch or so, you can't really damage it just from removing your item. Go ahead and flex the mold to remove the item.

As soon as the original form is removed you are able to use your mold. There are many things you can cast into the mold. Just as the silicon had a two part mixing system, there are kits that will cure into plastic or epoxy in the same way. I prefer to use plaster because it's cheap. Also, when using the vacuum former sometimes I need to break the form to get it detached from the plastic formed on top. Whatever you use, just follow the directions on the packaging.


These plaster bells are the result of my plaster casting method. They take about two days to get bone dry.


Stick around for the next few posts and I'll share more about what I'm working on at Tech Shop and what I need these plaster bells for. Talk to you later.

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