Do It Yourself Chocolate Molds

The Story:
Every year the company I work for (Logic) has a holiday pot-luck. Last year I made a robot that frosts cookies to bring. This year I had very little time because of all of the projects I was working on, so I went for something almost as geeky but with a lot less debugging required. I made chocolates in the shape of circuit boards and Legos. This year, there was a contest at the pot-luck, with a secret ingredient (which turned out to be ginger). To enter in the contest, you had to use the ingredient. I chopped up small pieces of crystallized ginger and put them into my dark and milk chocolate molds. It turned out to be a fantastic combination. I actually won the prize for most creative entry! Everyone made absolutely incredible ginger-laced foods, and a wonderful time was had by all.

I chose to make molds of my own UBW and UBW32 boards, as well as a product Logic makes called a Card Engine. Some various Lego pieces were thrown in just because as well. They all turned out really well, but the Card Engine boards were really cool. You could see the top copper layer traces, the silk screen, and the part numbers - all in the chocolate!

You will need:

Part A and Part B of the mold compound (silicone rubber) - I used Silicone Plastique from http://www.culinart.net/silicone.html
Some small thing you want to make a chocolate in the shape of
A box slightly larger than the thing you will be molding (optional with thick silicone)
Chocolate 'chips' to pour into the mold - I used Melt'n Mold from http://www.anoccasionalchocolate.com/molding-chocolate.html
A freezer to chill the chocolate
A plastic squeeze bottle (optional)

Step-by-step procedure:

Make a small box, about 1/4" larger on all sides than the thing you are going to mold. My object for this series of pictures was a Lego minifig, so I built a Lego box a bit larger than the minifig.

Take equal parts of the silicone rubber part A and part B, and mix them together by folding and kneading. Enough to fill the box. Mix until the color is uniform.

In order to insure that there are no bubbles in the mold, take small pieces of the mixed rubber (which has the consistency of play-dough) and press them tight into the small nooks and crannies of the minifig.

Take the rest of the rubber and push it into the box.

Take the minifig, and push him face first down into the box which should be almost filled with silicone rubber. Pushed down very straight and very hard.

Use a small screw driver to help push any little pieces of the silicone rubber into position. The trick here is that you can't have any silicone rubber 'overhang' - when you pull the chocolate out of the mold, it has to come straight up. So I pushed back the edges of the silicone where it had begun to overhang the minifig.

Let the mold harden. This takes about an hour for me.
Remove the mold from the box. I just slowly removed pieces of the wall (since it was Lego). Then gently remove the thing from the middle of the mold. Bending the mold, and working one part at a time helps. Don't try to do it all at once or the mold might tear.

Now melt the chocolate. I used a type of chocolate that is designed to be melted in the microwave, and it worked beautifully. I got dark and milk chocolate, and they didn't seem to act any different. You need to be very careful not to overheat the chocolate - the instructions that came with my chocolate were to put the chips in a bowl, set the microwave on %50 power (I used %40) and nuke for 2 minutes. Stir, then another 30 seconds. Stir, then another 30 seconds. Repeat just until the whole thing is liquid, no more.
Pour the liquid chocolate into a squeeze bottle.
Then fill the mold with chocolate from the bottle, begin careful to squeeze into the lowest nooks and crannies first, then let the chocolate find it's own leave as you squeeze more and more in. Stop when it is level with the top of the mold.
While the chocolate is still hot (don't take too long filling it) bang the mold squarely down on a tabletop. Many times. You'll probably see little bubbles coming up to the top. This banging gets those bubbles away from the edges of the mold, where they would ruin the appearance.

Put the mold into the freezer for 15 minutes.
Remove from the freezer, and very gently pry the mold away from the sides of the chocolate. This is the hardest part, particularly with very thin things like circuit boards. You'll get the hang of it after you crack the chocolate several times. Any mistakes can just be re-melted and go into the next batch. I had more luck trying to bend the mold away from the chocolate, and keep the chocolate completely undisturbed in the middle. Don't put any pressure on the chocolate at all, just on the mold.

Clean the little left-over chocolate crumbs up from the mold with a paper towel and do it again to make the next set.

Hints:

You don't need a box to put your mold in if you use the putty-type silicone rubber, but it really helps keep everything square (at least for me it did).
You don't need a squeeze bottle to fill your mold with chocolate, but it really helped me. You can just take a spoon and dribble the chocolate into the mold, but I found the bottle to be more accurate and much faster with less spillage.
If you mold circuit boards like I did, make sure to fill any 'underhangs' on the board with clay before putting the board into the soft silicone rubber. This would be things like connectors, under chip pins, underneath PTH parts or larger SMT caps, etc. You'll have to wash the mold out pretty good with soap once it's hard (because some of the clay will stick to the mold), and be sure to dry the mold very well before pouring chocolate because water ruins chocolate.
If you immediately re-use your mold to make another set of chocolate, the mold will be very cold (frozen). This means the chocolate really cools down fast when you pour it in, which means it solidifies fast. You have about 20 seconds from when you fill it until you can't bang the bubbles out anymore. Messing with it as it is setting up will make the top of the chocolate all bumpy and unappetizing.
If you press the silicone rubber onto a circuit board (small, thin pieces of rubber) very accurately (i.e. without it shifting around once it is placed) you can really reproduce the features of the board. You'll be able to see the solder mask, the top copper layer, and you'll even be able to read the part numbers off any any chips that were laser etched at the factory (most are). The level of detail you can get here is simply amazing.

Questions? E-mail me at my e-mail address