Revisiting Incomplete Open Cubes
Behind the scenes of an obsessive art project
The idea becomes a machine that makes the art.
I felt the first rumblings of the obsession a little over a year ago. I’m a big fan of Sol LeWitt’s wall drawings, and on a pilgrimage to MASS MoCA’s sprawling retrospective exhibition of them, I glimpsed some curious cube structures by LeWitt scattered around the museum. A short while later, in a used bookstore in Philadelphia, I stumbled upon a book which introduced me to the larger 1974 work those structures represented: Incomplete Open Cubes. To say it spoke to me would be an understatement. As I spent more and more time scrutinizing it, I started to notice avenues of thought the work had neglected or declined to pursue, ways that LeWitt’s definition of an incomplete open cube was less forgiving than my own.
I started sketching possibilities, first on paper, then in Adobe Illustrator, trying to work out a system that would produce the massive set of cube variations I envisioned (Fig. 1). After drawing several hundred variations, I started to recognize a formula that could be translated into code, so I moved over to DrawBot, which programmatically generates vector art using Python. A few days later, I had a script that created basic line drawings of the full set of 4,094 cube variations, and I layered in enhancements from there. Without getting into the nuts and bolts of the code itself (which you can explore on GitHub), let’s unpack the machine that makes the art.
How to draw 4,094 variations on incomplete open cubes

Define the parts
A cube is framed by 12 edges, so an incomplete open cube can have as few as one part and as many as 11 parts. Each part is assigned a number. Viewing the cube in isometric perspective, part one lies flat on the right side of 12:00 on the base of the cube. From there, part numbers ascend clockwise around the base, followed by the vertical posts, and finally the top (Fig. 2).

Find every possible unique combination of parts
The first 12 combinations technically aren’t combinations. Each consists of just one of the 12 parts. Those 12 parts are then each made the basis for a series of twopart combinations: onetwo, onethree, onefour, etc. Each twopart combination is then likewise made the basis for a series of threepart combinations: onetwothree, onetwofour, onetwofive, etc. Threepart combinations exponentially yield fourpart combinations (Fig. 3), which exponentially yield fivepart combinations, and so on down the line. As each new combination is created, it’s added to a master list of unique combinations. If the combination is already in the list, it gets discarded, which is more often the case than not. At the end of the process, the discard pile contains a whopping 20,481 duplicates, more than five times the amount of unique combinations.

Draw the unique combinations
Now that the heavy lifting is done and we have a list of all the unique combinations, the rest is a breeze, right? Well, not exactly. The vector art we’re generating is twodimensional and doesn’t inherently understand how the cube’s parts would interact in a threedimensional space. This can lead to some awkward overlaps that disrupt the drawing’s 3D illusion. There are two steps to dealing with this.
The first step is to change the stacking order. Try as it might, the numeric sequence of parts doesn’t quite match the way the elements need to be arranged in space. For example, part four should be behind part three, but it’s drawn on top of it (Fig. 4). If we change the parts’ stacking order, they’ll play more nicely together. A few different orders would work, but here’s the one I’m using:
 part 11
 part 10
 part 7
 part 3
 part 2
 part 6
 part 1
 part 9
 part 12
 part 5
 part 8
 part 4
Changing the stacking order helps, but it doesn’t solve everything (Fig. 5). Some parts just aren’t going to get along without additional intervention. Specifically, parts one, two, three, five, and nine need alternate versions in certain situations (Fig. 6):
 If parts one and four are present, use part one’s alternate
 If parts one and five are present, use part one’s alternate
 If parts two and six are present, use part two’s alternate
 If parts three and eight are present, use part three’s alternate
 If parts four and five are present, use part five’s alternate
 If parts nine and 12 are present, use part nine’s alternate
Now that everything is in order, all of those unique combinations can be drawn without incident.
As a novice programmer, it was pretty satisfying to figure out how to translate the process above into Python, even if my code is probably far less efficient than it could be. And as an admirer of Sol LeWitt, it’s a real joy to become so immersed in his work in this way. Incomplete Open Cubes is fertile ground, and this probably won’t be my last exploration of it. In the meantime, I hope you find this first result as mesmerizing as I do.