Samantha Skinner Compositor's blog

The making of: PotaDOS with Oomoo silicone

March 11, 2012 / by Samantha

So I decided for this up coming trip to Momocon 2012, I should make something really cool!

Just what.

I started to think about something I could make to add to my cosplay…then it hit me- I could attempt to make my own PotaDOS! Making it would not only be fun and a great prop making experience, but it would also add a new prop to my costume. Besides, I was getting tired of finding the ‘right’ potatoe and using it for only 3 days- Then getting oddly attached while having to disassemble and throw it out afterwords…

So I was then faced with how to make the PotaDOS. I started doing some research on line, then remembered one person in particular: Harrison Krix. He is well known for his prop making (Volpin Props). Harrison has not only made a Portal gun, but also an amazing PotaDOS talking replica. So why not attempt from the expert himself, right? I went right to his page to see if looking at his Flickr stream would help me get started.
Portal gun:
and, PotaDOS:
So, how are you holding up?

Now obviously, I was not going to make anything near this callibor. But I sure as heck was going to try!

I was reading the information on the pictures here; he wrote the line: “oomoo silicon 25″ and I decided to look that up. At the time I had no idea what it was, but had a hunch that I would need it. I found out that this is a brand of mold making material by a company called Smooth-On. I did more research on what exactly it was, then I researched the actual process of mold and cast making. After a few days I was able to locate a distributor and drive to them. They were absolutely wonderful and very helpful. I had lots of questions for them, and boy did they have answers. In fact, they did not find it too strange that I was molding a potatoe, only one person was a little curious, so I explained. After a lot of debate on what casting materials I should use, the strength on the silicon mold, etc, I bought my materials and I was off! I ended up with: Silicone mold 30, casting resin 65D, release spay, a seal spray, and some non-sulfer clay.

I left the store well informed and ready to go!

Now the next step: Off to buy the perfect potatoe!

Now for someone like me, this was a difficult task. Not to mention I was a little impatient and wanted to get home to work on making the mold. This picking process took me a good 30 minutes. And I am pretty sure everyone at my local target thinks I am a loon…. but! I ended up finding a suitable potato and going about my way.

I got home and took a picture of all my materials and posted it on my twitter account.

my materials

looking good so far! (even though nothing is actually made yet xD)

Like I said before, I was quite geared up to start that day. I got home around 5:00pm and I am definitely glad I did NOT start it then! This process needs a whole day! And that is just for setting the mold.

I decided wisely to start on my next day off and after getting a few things at the dollar store in the morning (some rubber bands, plastic cups, straws, popsicle sticks, and some rubber gloves,) I started my mold making around 11:00 am.

This process is definitely one that takes time to prepare for. If you plan on using these materials to make something, please plan it out ahead of time! These materials are a little expensive, but worth the price if used correctly.

I first went and made a mold box. Now I asked the people at the store about mold boxes, and unfortunately my original plan for a plastic box fell through…literally. The sides would not stick together. So I used a card bored one, instead. Works just fine as long as you spray the release agent on it before pouring the mold, and hot gluing the edges to keep a nice seal so no material can escape. I then added some tape just to be safe.

Once that was done, I added my non-sulfer clay to the table, then tried to push the potatoe half way through…which was really hard. So I ended up taking pieces of clay, and forming it around to make half. Always keep in mined- you are making one half of the potatoe at a time- So I wanted the clay to expose only one half first. After the potatoe and clay were all set, I added my pouring straw and my air bubble straw (the Smooth-On website has great tutorials as well!). I found out after the mold was done that I wanted a bigger pouring straw…I will get to that later. I also added some registration keys.

Mold Box and air release plus pouring vent

After this step, came the mixing step of the chemicals to make the material. It comes in 2 bottles with a equal mixing ratio. Once the colour was a uniform purple (pouring from one cup to another just to make sure), I poured it very nervously over my potatoe….

the first side done

Now as you can see, you ‘see’ the potatoe. For fear of not enough mixing material (or that I did my math wrong) I left it as it was. It worked out fine, but in the future I will make sure both half’s are completely covered. It makes the mold more durable.

This stuff is very sticky-you are going to want to wear gloves. I got it everywhere on the table, but I had it covered. Heh heh…get it? covered….oh, never mind.


After the allotted curing time (6 hours) I went and poked my mold (by this time it was 10:30 PM). Everything worked fine and I then decided to mix and pour the other half to have the mold completed for the next day, so that I could start casting. I flipped the box over, and started taking off the clay from the other side.

flipped and almost ready for molding

It was a little difficult, and I was very careful not to disturb the potatoe, but I got it done and poured and went to sleep.

I made sure to spray the ease release agent I had purchased because silicone will stick to silicone.

The next morning I had to remove the mold box walls carefully, and separate the 2 pieces of silicone. Every thing set perfectly. I was then onto the casting process. I do not have any pictures of the casting process. This can be dangerous, so please if you do decide to make this wear stronger gloves. These materials get very hot while mixing and can burn you (But it is still fun). :)

I got my materials gathered outside, and again poured them into a cup and began mixing. I read the directions and they mentioned having 2 minutes of working time. When they say 2 minutes, they mean it! This stuff hardens FAST! I actually only got a little bit in my first pour, and had to do it over 3 more times because my pouring spout was way to small (I got a knife and cut it bigger-being very careful. I actually damaged a little part of the mold, but taped it and it worked just fine). Do not leave the straws in once you start to cast with resins-the resin will stick to the straw making the resin set even faster over the hole!

To fix my problems, I made a contraption where I could ‘squeeze’ the resin into my mold. This was my 3rd and last try and I was getting very worried that I would have wasted all of the material. So I started once again pouring my material. This was my last chance to get it to work and slush cast! (slush casting is pouring the resin inside, then turning around the mold on all angles to get the resin to stick to the side walls, and not make a solid replica. This process will make a hollow mold) after I poured all the material, I waited 15 minutes before de-molding…


It worked just fine.

(completely removed):


Worked out- to my relief.

Now I am onto the job of painting it and prepping it for my electric parts- MWA HA HA!

Now unfortunetly due to lack of time (as of today, the convention is 4┬ádays away!) I had to purchase a…’cheater’ set of parts from Think Geek. I purchased their potatOS system. Once this convention is over I plan to make all the parts my self, but anyway-

I ordered the set and it came in with in a few days. Everything is working out so far except-

I have to now manipulate their PotaOS to work with out being plugged into a potatoe. Now the unit in general does not actually run off of potateo power, But it does detect when being plugged into one. So now if I put the two end pieces together, she talks like normal. So it works, I just have to figure out making it work properly (which I think I am just going to set it up like normal and add some wire to make the prongs touch to finish the circuit).

So now onto the next part:

Painting, and fitting the pieces together.

I recently bought a dremel so I think this will be somewhat easy, but I didn’t want to jinx my self. My resin potato is pretty strong, but I want to be very careful when drilling into it. I went from small to big, working on the main circle first. After tat was fitted, I added other holes to fit all the other parts.

I traced out the basic shape of the PotadOS unite, and went to work.

started and so far so good…

After what I am sure was an hour, I got the part fitted, then started drilling holes for the detail.


all drilled and happy.

Now I just have to prime, and paint!

Not this was not so hard compared to what was already done. I had already bought the brown paint, I just needed a good primer. So, I decided to drive to my local Home Depot and get some paint. Walked all around the store, got to the front, was getting checked out and I was all happy until I realised I forgot my wallet. My wallet…really? I had to runto my car (which I was now driving with out a license) back home and get it. I felt quite scatter brained, but I think I will blame that on my cold….

anyway, I got it and went about my crafting.

primed and painted- first coat.


So now I am pretty happy with how and where everything is now. I think I can now take my time and hand paint details if I so choose.

Like I said before though:

I do plan on making the electric components once I have time on my hands after the convention. A lot of love and time went into my PotaDOS and I hope it turned out to others looking good as well. I think it looks good to me, but maybe I am a little bias….:)

A little on Momocon 2012:

I am seriously so excited to go. I will be bringing this potatoe and hopefully a few other costumes with me. I can not state enough how thankful I am (Chris! (: ) and how excited I am to meet Ellen. She is my idol. I am counting down the days and it almost feels like I am counting down the seconds. This will probably be the best convention I will go to. Ever. I am also excited that Volpin will be there as well. (I just wished I was able to make the electrical parts of the potatoe and show him more proudly in that department,) but! I am still proud non the less. I would love for Ellen and Harrison to sign my creation :).

thank you to all who read my entries so far. Much appreciated ~

Don’t forget to read my other entry about where I got to talk to Ellen Mclain in a surprise interview!

2 thoughts on “The making of: PotaDOS with Oomoo silicone

  1. Phil F says:

    This looks fantastic, I’m making one at the moment but fortunately do not have a time frame to do it within, which makes it a little easier.

    I have met the same hang ups as you with quick setting resin and will be doing another one today :)

    What paint did you use on the resin?


    • Samantha says:

      Hello Phil!

      Thank you~
      Quick setting resin definitely made the job a challenge! I was worried I was going to run out and I almost did. Thankfully I got the hang of making a hollow mold on the third try ah ha ha.

      I ended up using regular spray paint. I found a good spray paint primer and painted a base coat, waited for that to dry, then spray painted the layers of brown to give a”potato skin” feel.

      (I think the brain might have been rustoleum or something)

      – Samantha s.

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