Mold Making and Casting 101 With Smooth-On

Comic Books Geek Culture Movies Products Reviews Tools

SmoothOn-SloganI wanted to finally dip my toes into the amazing world of molding and casting props so I turned to the experts–Smooth-On.

Everyone who is anyone that makes props in the cosplay world seems to use Smooth-On products. After watching video after video from Punished Props, Volpin Props, and CoreGeek Cosplay and Creations (seriously, if you’ve any interest at all in making your own props, visit all of these sites regularly), it was a very easy decision to go to Smooth-On for my first time. For Emerald City Comic Con I am doing an Ashitaka cosplay, and I needed to make arrowheads for my arrows. I had originally planned to make them all out of foam, but being able to make them quickly and identically appealed to my better nature and seemed the perfect first project for mold making and casting.

Smooth-On care package. Photo by Will James.

Smooth-On is a company for geeks by geeks. They are super knowledgeable to the lengths and depths we geeks are known for. They are also friendly and more responsive than just about any company I’ve ever spoken with. I sent them a message asking for their recommendation for a newbie, and they immediately responded and sent me out a little starter kit that included Mold Star 15 SLOW Silicone Rubber, Smooth-Cast 300 Resin, and a Super Seal and Ease Release 205 Combo pack.

Mold Star 15 and Smooth Cast 300 are both really easy to mix and use because you just need to pour out equal parts of the A & B and mix them together. Some of the other types of mold and casting products require more measuring and mixing so these make it great for beginners. While the Super Seal and Ease Release aren’t critical to your project, they will help ensure that your mold comes off of your master nicely without soaking in to it or getting contaminated by it and the release will help ensure clean castings.

Mold Star, Sealer and Release, and mixing supplies. Photo by Will James.

The only other supplies I needed to buy that I didn’t have on hand were mixing/measuring cups and stir sticks and some plastic to make my mold box out of. I just got a piece of scrap from a local plastic store but any sheet plastic should work for you.

Once I had all of my supplies on hand, I broke out my Van Aaken modeling clay to sculpt the master. If you’re making your master out of clay it is critical that you use a clay that does not contain sulfur or the molding rubber will never cure. The other nice thing about an oil-based clay like Van Aaken is that, assuming you don’t care about the master once you have your mold, it never dries out and is completely re-usable.

Master sculpt with clay. Photo by Will James.

I looked a lot of different stills from Princess Mononoke and every one had a different looking arrowhead, so I Googled ancient samurai arrowheads and used those as inspiration to design my own. It’s a little chunkier than the real thing would have been, but these are a prop and I wanted them to be visible and stand out in photos. I also decided that, because this was my first attempt at this, I’d make a single mold versus a two-part mold (but I will be trying that next). It meant having to cast ten arrowhead pieces to make my five arrowheads, but I decided it was worth it to spend a little extra time casting (ten minutes for each piece) versus screwing up the mold and casting on a two-part and wasting a bunch of material and having to start over.

Mold box. Hot glue is cheap and plentiful! Photo by Will James.

Once my master sculpt was all done, I measured and cut four “walls” from my scrap plastic. I then hot glued them all around the master, making extra sure to use a bunch of glue at all of the seams to prevent my rubber from running out all over the place. Then I followed the directions on both the sealer and release to prep my master and box.

Mixing and pouring the silicone rubber. Photo by Will James.

I measured out my A and B parts of my Mold Star into separate cups. it’s recommended to measure them out individual, mix them individually, and then pour them together and mix them. Once everything was all mixed up, I was ready to pour. Mold Star 15 SLOW has a 50 minute pot life which was nice to be able to take my time for my first try at this without feeling rushed. Now that I’m relatively confident with what I’m doing, I’ll probably wish I had something that cures faster, but a four-hour cure time isn’t going to be the end of the world since I’m not doing anything with very strict time tables yet. Doing a long pour (a la Cocktail) is the best way to ensure you don’t get any trapped bubbles in your mold if you don’t have a degassing chamber (which, as a newbie, I do not).

A perfect mold on my first try! Photo by Will James.

I let the mold sit overnight to give it some extra cure time and then went for the jailbreak. I broke down my mold box and then peeled the mold off of my master. It was perfect!

Oops. Not so perfect on my first casting. Photo by Will James.

Just like with the master, the mold is prepped with release as well to ensure you get good casting pulls without anything sticking. Some folks will use cornstarch or baby powder lightly dusted in their molds as a release, and I’ll probably try that at some point, but, since I had it, I used it. Just like with the Mold Star, I measured out my equal parts A and B of the Smooth Cast, mixed them together and poured it into my mold. I poured in too much, which resulted in a little bit of flashing and the need for extra sanding when all was said and done. What’s really cool about watching the resin cure is that you can actually see it hardening. Also, because the curing is exothermic, the thicker parts actual cure the fastest.

I wanted to try to get gray arrowheads so picked up a different brand resin tint and it didn’t mix very well with the Smooth Cast. I’ll be getting some So Strong Color Tint from Smooth-On before I try it again.

Waste resin from each of my pours. By the end, my waste was nothing more than a thin layer of resin that coated the inside of the mixing cup. Photo by Will James.

With each casting, I got better at measuring out how much resin I needed and by the end, I had almost no waste. Unfortunately, it wasn’t until I was all done that I found this awesome materials calculator on the Smooth-On website that will help you figure out almost exactly how much rubber and plastic you need for your pours to make sure your supplies go the distance and you waste as little as possible. Don’t be like me and use the calculator from the get go!

I also found that if I poured in just a little bit of resin and did the slush casting technique of coating the entire mold with a thin layer before pouring the rest in (immediately), it helped break the surface tension at the top of the mold making the flat side more flat. It’s not a big deal but it meant a lot less sending to get the later pieces ready to glue together.

Glued, puttied, and sanded. Photo by Will James.

I then super glued the halves together and puttied up any gaps or uneven spots. Once that was dry, I wet sanded everything down until it was 95% smooth.

Filling primer is magical. Photo by Will James.

My next step was to use some filler primer (this stuff is genius and works really well to fill in that last 5% of gaps to get a really smooth finish.

Those are black pants. Lots of sanding dust which is why a respirator is your most important tool! Photo by Will James.

I then broke out my Dremel to drill out holes for my arrow shafts. The resin took my Dremel drill bit nice and easy and I was able to shape it to the exact size I needed for a nice snug fit.

All metallized and nowhere to go. Photo by Will James.

Next time I want to make metallic looking castings, I’m going to try cold casting with the metal powders available through Smooth On. But because I was trying to keep it simple for this go round, I instead opted to use DecoArt Metallic Lustre Wax. This is a metallic wax paste that you can rub on just about anything to make it look metallic. I love how these came out looking like they actually were cast metal.

Arrowhead weathering. Photo by Will James.

Once I was pretty happy with how the arrowheads looked, I broke out my acrylic paints to give them a little touch of weathering to make them look more realistic. Coincidentally, I had just received Bill Doran’s Foamsmith 2 book the day before I got to this point and got to use the weathering techniques from the book right away! I love being able to apply new-found knowledge to a project immediately!

Finished set of arrows. Photo by Will James.

And the finished product looks amazing (if I do say so myself)! I can’t wait to show off these arrows at Emerald City Comic Con this week. Hope to see you there!

Liked it? Take a second to support GeekDad and GeekMom on Patreon!

3 thoughts on “Mold Making and Casting 101 With Smooth-On

    1. I used some Squadron putty I had laying about from my hobby modeling. I’ve since done a bigger project and bought Bondo in a tube. The primer I’ve been using a lot is the Rustoleum 2-in-1 filler primer. It helps smooth things out in addition to being a nice primer. With wetsanding you can get a really smooth finish. Here’s the project I used bondo and primer on :

Comments are closed.