As I mentioned in my last post, Chapman, my brother, made a special request of a set of oversized yahtzee dice for a wedding present. He and his friends have been enjoying outdoor lawn games, and he wanted an enormous (12-16" cubes) set of yahtzee dice to play yahtzee in the park. (He also wanted them for use at his rehearsal dinner/crawfish boil.) Since they were a special request for a special day, I had to do what I could to fulfill it.
Flexible pourable urethane foam was not the first idea for making the dice. Some earlier ideas included sewn cubes stuffed with polyfill, sewn cubes with a wire frame insert, and acoustic insulation cubes with painted pips. The first two ideas were finicky: fabric cubes generally don't hold their shape well, so I didn't have confidence in their long-term performance as dice. Before we thought of the pourable foam, the third idea had the most promise. Auralex acoustic foam is only available through distributors, and the price per die would be very steep. If you want to make a large-scale yahtzee set without making a mold and pouring your own dice, you could go that route, and the only remaining step would be painting the pips.
Bryan saw a demonstration of pourable urethane foam which put us on the path of pouring the foam into the shape of dice. Rigid pourable urethane foam is easy to get as it is used by many boaters; however, it can be brittle which isn't a desirable quality in something you want to throw around. Once I found flexible pourable urethane foam I knew we had a winner. I originally wanted to use Smooth-on's flexible foam; however, the shipping was too expensive as it was more than the price of the actual products. (If you've ever wanted to make your own props or unique toys, check them out: they have some cool stuff!) Since ordering directly from Smooth-On was cost-prohibitive, I looked into their local distributors and found Douglas & Sturgess in Richmond. After visiting their store, I left with a box full of chemicals, urethane foam informational sheets, advice on how to complete the project, and a smile on my face. If you're local to the Bay Area, I recommend them for your extreme crafting needs!
The process of making the dice was to (1) make the mold, (2) pour the dice, and (3) paint the pips and seal the surface.
1) Making the mold:
There are a few ways you can make a mold to cast urethane foam. If you want a complex shape, you can use a positive of your desired end result and pourable silicone to make a two part mold around it. As the desired end shape was simple, we simply made a negative of the desired end shape.
We used 10 3/4" melamine coated boards (sold for use as shelving) to make a mold where the inside was a 10" cube. After a false start, we ended up with a three part mold that could separate into four to release the die. The first two parts, the top and bottom, were identical except that the top had a 1 1/2" hole through which we could pour the foam. The third part, the side assembly, could separate into two halves during the un-molding of each die. The side assembly was held together by screws and was simply unscrewed during the unmolding process. Mold straps held the top and bottom snugly against the side assembly while the foam cured.
2) Pouring the dice:
Rising foam (Pictures 1 and 9 were taken less than 30 seconds apart)
Pourable urethane foam expands quickly, so you need to have everything in place and work quickly once you begin mixing the parts together. After expanding, the foam needs to cure for an hour or two before you can remove it from the mold.
Before each die was poured, we applied a release agent so that the foam would separate from the mold after it cured. We used sonite wax followed by a layer of baby powder. Before assembling the mold, the wax and baby powder were applied to the interior surfaces of the mold, the top and bottom edges of the sides, the pour hole in the top, and the outside of the top.
The baby powder application took a few tries to master, but it was a lot like flouring a very large cake pan.
The pourable foam used was a two part foam. Parts A and B were measured by weight in separate containers before part A was mixed into part B. If you don't add any tint, it comes out somewhere between cream and goldenrod yellow. Chapman wanted grey dice, so we used two pigments, white and black, which were added to part B of the mixture before the two parts were mixed. The dice are a 50% grey; they are equal parts white and black. As suggested by Todd from Douglas & Sturgess, we used a drill paint mixer attachment to quickly and efficiently mix parts A & B.
As soon as it had been mixed (we went for 10 seconds) we quickly poured the foam into the mold. Since the mold was pretty large, we quickly (and carefully!) rotated the mold to coat each surface with the foam while it was still in the cream stage. This awkward step was also recommended by Todd, and it really helped to reduce bubbles on the surface of the dice and help the foam climb up the sides of the mold. To keep the drill attachment from being single-use, we soaked it in acetone to remove the foaming polyurethane.
After the foam had expanded to fill the mold, we let it cure for an hour and a half to two hours before beginning the unmolding process. To unmold the dice we removed the straps, gently pried off the top and bottom pieces, separated the sides into two halves, and removed the die from the mold. After each die was unmolded, we screwed the sides back together.
3) Painting the dice:
Douglas & Sturgess makes a great product that they call Snakeskyn. Snakeskyn is the consistency of a thick simple syrup and dries clear, flexibly conforming to and protecting poured urethane foam. I added a black Mixol tint to the Snakeskyn to paint the pips, and then painted a clear protective coat after they dried. To make the pips of the dice a consistent size and shape, I made a stencil from a piece of plastic. I also made a stencil for the layout of the pips.
Before starting to paint the dice, I washed the dice so that no trace of the release agents (sonite wax and baby powder) remained. This was to allow the Snakeskyn to firmly attach to the surface of the foam instead of the release agent. After washing the dice, I used a permanent marker to mark the center of the pips on each die. The center guides and the stencil made it simple to paint uniform pips. I found that it took a couple coats of the tinted Snakeskyn to get the pips dark enough. Once the pips were dry, I applied two coats of clear Snakeskyn to the surface of the dice using a mini-roller.
If you know in advance you're going to make either a bunch of dice or something else that requires multiple pours per item, I would suggest mixing the tint into all of your part B in advance for a uniform color between all items/pours. We counted the drops and did the same ratio each time; however, there is still a slight difference in color between the dice. We found that the color of part B once the tint was mixed in was pretty close to the finished color of the dice.
We needed about 30% more of the foam than would be expected to fill the volume. We poured the first die using the amount calculated using the foam density and mold volume and ended up with something that resembled a loaf of bread from a bread machine, not a cube. After the 30% increase, we found that if we added more foam, it left the mold as flashing and run-off.
Despite our best efforts, we did end up with some voids which Mary & I were able to fill in with an small batch of foam. Keeping the die in the mold was crucial to our success in the foam repair. The foam has a different final texture if it forms in a mold vs. if it is free-formed.
Temperature is important to the process. The foam rises slower and is easier to work with at lower temperatures, resulting in more even sides to the dice. We also found that some of the dice collapsed in on themselves an hour or two after the unmolding. The first one to do this bounced back within a day or two, while the other two dice took longer to return to normal.
This was a fun project! This was not a cheap adventure; however, the end result was well worth it! They have a satisfying heft and feel substantial and well made. They look much better than the expected result of the first two options considered, and most of the people who played with them at the crawfish boil were unaware they were handmade until my brother told them. (He got a few inquires as to where he purchased them.)
The dice are really fun to use. There were a few main methods people employed to roll their initial die roll: some did their best to pick them up and throw them in one group while others stacked them and then attempted to knock the group over. Once you get to secondary rolls, it's much simpler to pick up a single die and roll it.
A special thanks to Mary & Steve who helped Bryan and I pour all the dice!