Most people would tell you that a 3-year-old's birthday party is likely to involve quite enough carnage and demolition without any help from the cake. I am not one of those people, especially since my 3-year-old nephew Nathan in extremely passionate about demolition, construction, and more or less anything that involves big machines.
So I thought that a wrecking-ball cake would be ideal for his demolition-themed birthday party (if that isn't bowing to the inevitable, I don't know what is.) Of course, a wrecking ball cake that didn't actually wreck anything would be utterly pointless, so my first step was to come up with a good, working wrecking ball mechanism. I was concerned that if I made a wrecking ball that simply sat next to the cake that it was intended to wreck, the composition wouldn't be unified enough. I also didn't want to have to make an entire crane to support the wrecking ball. So I came up with a plan where a wrecking ball would rise up out of a circular cake and spin around in a complete circle, knocking down a series of gum paste buildings around the perimeter. This concept was also nicely in keeping with my series of self-destroying cakes, previous examples of which include the Melting Head Cake, the Fountain Cake, and the Self-Digging Cake for Nathan's second birthday.
The wrecking ball mechanism consisted of a brass tube attached to a hobby motor, which spun inside another, larger-diameter brass tube. The hobby motor was encased inside a piece of PVC tubing, so that the cake (with a pre-cut hole in the middle) could just be slipped around it. The spinning tube had a hole drilled in the tip, to which I could tie a little piece of wire, the other end of which would ultimately be attached to the wrecking ball.
I went through a few iterations of wrecking ball tests. My first plan was to make the wrecking ball out of hard candy, embedding the wire in it when I poured the sugar. They turned out OK, but then I got worried that the sugar ball might shatter when it hit the cake and I also bought a silicon sphere mold that resulted in sugar spheres that were altogether too big and heavy for the power of the motor. My next idea was to make the wrecking ball out of marshmallow, on the theory that marshmallow would be tough enough to break the cake but spongy enough not to shatter. This turned out not to work at all, as homemade marshmallows are significantly poofier than commercial marshmallows and couldn't wreck their way out of a wet paper bag. Proving that old axiom that the third time is the charm, my third idea was modeling chocolate. This way I could roll balls of modeling chocolate to whatever size I desired, then punch holes through the center to attach the wire. This worked well, except that on my first try I only ran one wire through the middle of the modeling chocolate ball, and when I turned the wrecking ball on the wire just sliced right through the chocolate and the ball went flying. I found out, however, that if I distributed the wires at four points around the ball the centrifugal forces were dispersed enough that the ball stayed intact. I also covered the ball with a layer of royal icing and a dusting of powdered colors to make it look more iron-like.
With wrecking ball methodology ascertained, the next step was creating and decorating the cake base. The bottom of the base was a simple plywood circle, but I also needed to layer some foamcore on top of that to hide the battery, wires, and switch for the wrecking ball. To get a little color into what promised to be an otherwise fairly drab-colored cake, I painted yellow and black caution tape stripes on the plywood. I then put a smaller circle of foam core over top of this, with appropriate holes for the battery and such, and covered that with a tiled pattern of marbled fondant. Actually, I did this twice because I didn't like my haphazard arrangement of shades of grey the first time around, so I tore it up and redid it with a much more careful pattern.
Now having a base for my cake, I set about making the sides and top. For the top of the cake, I made a circle of marbled fondant with a pre-cut hole in it for the wrecking ball. By letting this dry for a week, I wound up with a nice rigid circle that would give me a much cleaner, more architectural finished cake than I would get by covering the cake with soft fondant after it was baked. This resulted in me making the interesting discovery that blue food coloring turns green when exposed to sunlight. Fortunately, it still looked OK with the rest of my cake color scheme (at least it was a cool, grayish-green) but hopefully this can help prevent potential problems in the future. For the sides of the cake I made a series of very dark blue and purple gum paste rectangles, which looked fine, but, due to the massive quantity of food coloring involved, tasted revolting. Perhaps next time I should start with chocolate fondant.
Now all I needed was something for the ball to wreck. In order to get something that would shatter nicely, I opted for skeletal buildings made of gum paste, rather than trying to smash through actual cake. I still wonder if that was a bit of a cop-out. I made a series of eight skeletal framework buildings of increasing height. I calculated that, in total, they required just over 300 feet of gum paste strips. It was a bit of a time-consuming process because I first had to roll out the gum paste, then cut it into strips and use a bit of brass tubing to create a riveted texture. Once the gum paste dried, I could cut it to the appropriate length, and then stick three pieces of each length together with royal icing to made "U-beams". (I thought about making I-beams, but decided that would be more difficult and wouldn't look as good.) After the U-beam royal icing dried, I used more royal icing to put the pieces together into each of the three sides of each of the eight buildings. I then had to wait for that to dry again before I could stick the three sides of each building together. In other words, I spent about two weeks every day after work hunched over my table sticking tiny grey bits of gum paste to other tiny grey bits of gum paste. Whee!
Once the buildings were done, I had to make the expanded steel (by which I mean royal icing) inserts to go between the gum paste girders. Fortunately, this went a lot faster than the gum paste project, even considering that I was also piping lots of royal icing chain link fence that was ultimately destined to go around the perimeter of the cake. I used a #2 and a #1 piping tip, so my hand did get a little sore, but that's to be expected.
Once the royal icing was dry, I just peeled it off the wax paper and stuck it into the holes of the gum paste buildings with a little more royal icing.
At this point it seemed that I really should make some actual cake to include in my cake. This was probably the easiest actual cake I've ever made, since I actually wanted it to be round, which just so happens to be the shape of normal cake pans. So, for once, no cake carving, no giant pile of gooey cake scraps, just some torting and filling, and making sure that I would up with a cake the correct height to fit with the premade buildings. I did have to cut a carefully angled hole in it to accommodate the wrecking ball mechanism, but compared to my usual practice of carving cakes into the shapes of rats and human heads and such, it was quite easy.
With the cake in place around the wrecking ball, it was very quick work to slap my pre-made top and sides on and place my eight building around the perimeter. I also flung some edible glitter on the sides to give it a little more sparkle.
From there it was a simple matter of placing the fence pieces, and strewing a few broken bits of girders and such about to give it more of that "in the process of demolition" feel. In retrospect, it might have made a stronger artistic statement if I had started with a complete building and wrecked that, rather than starting with an already wrecked building and simply wrecking it more.
At this point it occurred to me that, as I was making this cake for a three-year-old's birthday party, it might be a good idea to incorporate some birthday candles into the design. Considering that they were a complete afterthought, I thought they turned out rather well. I encased the three candles in various heights of leftover gum paste girders and stuck them to the chain link fence, right behind the switch that turned on the wrecking ball.
To bring the whole composition together, I added some black food coloring shadows into the seams between the buildings and the cake itself and I added some bright yellow highlights to the buildings, which picked up the yellow paint on the bottom base.
The finishing touch - little royal icing people watching from outside the fence. I like to make my sugar crowds along the same lines that I make my scale figures when I draw set sketches for the plays I design, keeping the people blank, white, and anonymous so as not to distract attention from the scenery or the cake which is the true focal point of the piece. In cake form, this tends to give my crowds a bit of a zombie-horde feel, which, as you can probably guess, I really enjoy.
The presentation of the cake at the party went quite well. Nathan was excited about tuning on the switch, but he's sort of a cautious guy, so he also kept turning it off and his friend Noah would turn it back on. So the destruction proceeded a bit in fits and starts, but eventually the ball reached full speed and full destructive capability. I wish I had made the wire on the wrecking ball just a tad longer, because I think it would have made the destruction more impressive, but all in all I was extremely pleased. And Nathan looked delightfully like an angelic little blond Godzilla gnawing on the broken girders.