When it comes to serving a chilled drink, you can use cube-shaped ice like adults do—or you can show your eternal youth with custom ice replicas of your favorite toys. With a few basic supplies and a bit of patience, you can make a reusable mold to cast frozen replicas anything—even a baby doll head that's just about the right size for a rocks glass.
You Should Do This If:
You love Batman so much you actually want to ingest him.
Moment of Satisfaction:
Watching a block of ice shaped like a human head slowly melt into a glass of bourbon.
Biggest Pain in the Ass:
Not being able to reenact the latest Avengers trailer while waiting for Mjölnir's silicone grave to firm up—some mixtures can take up to a week to cure.
Materials and Tools Required:
- Small, hard toy without too many hollow features
- Container that closely but entirely fits toy
- 10-ounce tube of clear 100 percent silicone caulk (but not "Silicone II"), caulking gun, and cornstarch (or use Sugru or a catalyst-driven food-safe RTV silicone from Smooth-On)
- Popsicle sticks
- Plastic cups, spoon and knife
- Non-stick food spray (canola oil worked well)
- Wax paper or aluminum foil
- Duct and masking tape
- Nitrile gloves
- X-acto knife of sharp box cutter
- Well-ventilated work area and/or high quality filtered respirator
On a scale of one to ten, five.
About $20 if you mix your own silicone. Lots more if you buy the real stuff.
1. Set up a mold box. I did two castings: The decapitated head of a baby doll from the 99-cent store, and a Storm Trooper. Each required different molding techniques—a firm, two-part mold for the figure, and a one-piece, supple, peel-able mold for the baby head.
For the Storm Trooper, I used a plastic storage box for cream cheese that left about 1/4-inch of silicone on all sides. A quart-sized plastic yogurt container fit the doll's head. You can also use Legos or a duct tape-lined cardboard to build a mold box. Professionals make theirs out of high-quality plywood. Just don't pick something much larger than your object or you will waste silicone.
2. Plan placement. Because of their pesky limbs, figurines need to be cast with a two-piece mold, otherwise you would never be able to extract them from the hardened silicone. They work best when molded front and back, with the seam running down the side.
All molds need an opening (called the sprue) where you can pour in the casting material. I affixed a segment of a plastic straw to the back of the Storm Trooper for mine. Air holes at the ends of long narrow sections (legs, arms) help the water flow through without getting blocked—toothpicks work well for this. And look out for narrow segments on limbs; the skinny joints on my Storm Trooper's knees caused weak spots that broke easily when the ice was removed. Reinforce those areas by adding putty to thicken them up before making the mold.
Deeper objects with less extremities (like the baby's head) can work in a one-piece mold made from a softer mix of silicone, then peeled off after casting. Sometimes cutting the mold will be necessary to get past a tight sprue. I let the neck of the baby head extend out of the silicone as my spot to pour in the liquid, and then cut it halfway apart when taking the head out.
Once the container, sprue, and placement are determined, give everything a healthy spray of canola oil. This will help keep the silicone from becoming permanently stuck.
3. Mix silicone. Note: Although inert, most silicone caulk isn't listed as food safe, nor is Sugru (although they're working on FDA approval). There are varying reports that once cured, the widely-available GE Silicone I (but not Silicone II) may be okay for this type of use, but if you don't like living on the edge, get a food safe silicone putty like this stuff on Amazon.
Standard silicone caulk, poured thick, will remain liquid on the interior—not useful for mold making. You can force it to harden throughout by mixing the silicone with cornstarch (as pioneered in this Instructable by Mikey77), which provides the necessary moisture needed for the silicone to completely harden. But when it does, it releases a strong acidic odor, so make sure to have good ventilation or a good respirator for this part. And use a sheet of aluminum foil as a work surface, instead of gumming up your dining room table. I wrap a piece of plywood with foil for a transportable work surface.
For a fast-curing, firm rubber mold, use one part silicone to two parts cornstarch—squeeze the silicone into a cup, shake the cornstarch into two similar cups, then pour everything into a larger container and mix thoroughly with your plastic spoon, knife or Popsicle stick. It might seem that there is too much starch for the silicone, but keep mixing and cutting through it and eventually it will all absorb and you'll have a sticky, wet paste. You can also mix this by hand right on your work surface, like kneading pizza dough. Wear gloves. Keep a small dish with cornstarch nearby for dipping, and the silicone won't stick to your gloves. This mixture only takes a couple minutes to start getting hard, so be prepared to work quickly.
For a runnier batch of silicone, use the reverse ratio (two or more parts silicone, one part cornstarch) and add in one part distilled water. This mix will flow over details easier and minimizes troubling air pockets, but will take longer to cure—possibly a lot longer.
4. Mold a toy. For the Storm Trooper, place a layer of the silicone mix on the bottom of the plastic container, thick enough to cover the front half of the figure. While still supple, carefully but firmly press the oiled figure into the silicone. The goal is to get all of the figure's details surrounded and covered, without gaps or air pockets. But make sure you don't push it all the way through. Get an even level of silicone around all sides, as close to the halfway point as possible, without any parts fully covered. This will make extraction easier.
While still hardening, use the edge of the Popsicle stick to press a 1/8-inch deep impression around the figure, tracing its details but not touching it. This will be the key that will help keep the top of the mold perfectly aligned, and will also act as a gasket to keep water from squeezing out or having excess ice flashing where the two halves meet.
For the baby head: start by lubing it well with oil (which might be the creepiest thing you'll ever do). Then goop a thin silicone coating onto the entire exterior of the head up to the neckline, making sure the details are perfectly coated. Pour the silicone into the bottom of your plastic container, then push the coated baby head into the silicone, adding more to fill up the container as needed. There is potential for large air bubbles to get trapped inside the silicone during this part, which will cause undesirable voids, so be careful to pour and mix it in smoothly. Allow the neck to remain exposed and set this aside to firm up.
5. Wait. For the thicker silicone/cornstarch mix, this should be firm in about 30 minutes. For the thinner mixture, it took about five days to reach the right firmness.
6. Make a mold top. (This is for the two-part mold only.) Once the front half of the mold feels solid, give everything another coat of nonstick spray. Forget to do this and you'll probably never get your toy out from the two halves. Mix up another batch of one-to-two silicone/cornstarch, and working quickly, press the mix firmly into the container, working from one end towards the other to surround the figure while avoiding pesky air pockets (use those cornstarch-powdered gloves for this, or spritz them with oil). Allow the sprue and any toothpicks for air holes to remain exposed, and if you're picky about things, use the back of the plastic spoon (lubed with oil) to smooth the top of the silicone as it cures. Bonus points if you slope the silicone inwards towards the sprue and air vents.
7. Remove the original. The hardened silicone will have the tendency to stick to the container. You'll have to start working it loose—a few spritzes of canola oil between the plastic and silicone (spread apart with an oiled Popsicle stick) helps things drastically. If you made your own box out of legos or wood, simply disassemble it.
Take out the object you are molding and inspect the inside of both sides of the molds. No air pockets or voids? Keyed gasket filled in? Holds together nicely when put back together? Good job.
For the stretchier, one-part baby head mold, press around the silicone to find the thickest area. Then, from the neckline, carefully cut a line towards that side. Get a sense for how far you'll have to cut to remove the head without tearing the mold. Some spritzed canola oil helps with the release. Looking back, I could have probably made a smaller cut for mine.
You should now have a mold with an inverted duplicate of your toy.
8. Freeze stuff. Clean your mold with warm soapy water, just to be safe. Close the mold and wrap some tape or rubber bands around it to keep it sealed, but not so tight that the rubber distorts. For the opening on the mold for the baby's head, a few pieces of tape were placed to seal the rubber.
Fold a long piece of duct tape onto itself and place under the mold, extending outwards. Stick this into the same container used to make the mold. The container will help make sure the mold maintains its shape, and the duct tape will act as a handle to help remove it when taking it out of the freezer.
Carefully pour water into the sprue and let it flow up until you see it start to peek out of the air holes. This is where the sloped exterior comes in handy, keeping any spills from getting all over the outside of the mold.
Carefully put this in your freezer, and wait a few hours. The insulating silicone rubber makes it to take longer to freeze, but also helps get a clearer piece of ice. Small pieces like the Storm Trooper take about three hours; the baby's head took twelve hours and still had some liquid on the inside.
9. Party. Put your creation in your favorite libation and feel the incredible freedom of never having to cool your drink with cube-shaped ice again.
Don't have time to make your own? You can get one of these, custom-made, by me, in my online store.
Mike Senese is a science geek who blows stuff up as the host of TV shows like Punkin Chunkin, How Stuff Works, and Catch It Keep It. He's also a freelance writer who regularly contributes to Wired magazine. Get inspired by Mike at his DIY projects blog, and follow @msenese on twitter.