I found this draft of a post in my backlog and decided that it would be better to finish it than to leave it unpublished. Actually, the story happened already over a year ago.
Some month ago I stumbled upon this piece of shadow art
by Fred Eerdekens and a few days later I received the information that my university was going to celebrate his yearly “open house event” this year as “TU Night”. The theme of the TU Night was “Night, Light, Energy” and all member were invited to submit ideas for talks, experiments and exhibits.
The piece of shadow art prompted the question “If this weired piece of metal can cast this sentence as a shadow, wouldn’t it be possible to produce another piece of metal that can produce two different sentences, when illuminated from different directions” Together with the announcement of the upcoming TU Night I thought if one could even produce an exhibit like this.
Since I am by no means an artists, I looked around at my university and found that there is a Department of Architecture. Since architects are much closer to being artist than I am, I contacted the department and proposed a collaboration and well, Henri Greil proposed to have a joint seminar on this topic. Hence, this summer term I made the experience and worked with students of architecture.
In the end, the student produced very nice pieces of shadow art:
Although the exhibits produced interesting and unexpected shadows, no group of students could make it and produce two different shadows out of the same object.
However, some nice effects can be produced pretty easy:
The basic idea is that moving one object around will move around both shadows rather independently. Well this is not totally true but what you can do is to “zoom” one shadow while moving the other sideways (just move the object straight towards one light source). See this movie for a small illustration:
I also did my best to produce a more complex object. While it is theoretically not very difficult to see that some given shadows are possible in some given projection geometry, it is not at all straight forward to produce the object theoretically (not to speak of the real world problems while building the piece). It tried hard but I could not do better than this: