This was a really fun one, inspired by a trip to the SF Exploratorium. By suspending soap between two sheets of clear plastic and passing a point source of light through the dripping soap, you can create some amazing caustics (complex focused light patterns).

---

I think the pictures that you get from this process are awesome. You can keep flipping the system over to reset and get a new, continually changing pattern. The best way to view it is definitely as a video but here are some images as well.

 

The basic design is (small point light source) → (dripping soap between clear sheets) → (projector screen of thin white fabric). I trap the dish soap between two clear sheets of acrylic with a nitrile rubber gasket in between. You can see the Onshape CAD files for the design here.

The projector suspends a small but powerful (adjustable) LED below the device:

I made it so that the circular viewport can easily spin around the horizontal axis, this way you let the soap drip, then flip to reset the process:

The projector screen is resting on a hand-carved piece of insulation board (this was the third projector screen attempt). The screen cloth is inflexible, and an elastic string has been stitched around the edge. By stretching the elastic string over a series of pins the screen is evenly pulled around the board.