In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
The series of photos of the 1959 model ends or stops with the photograph in which Kiesler triumphantly shows us the shell of his house like the remains of a creature taken from the seabed, a kind of Moby Dick harpooned and finally captured after the obsessive pursuit of a project that has taken up ten years of the life of the architect.
"I think that everybody has only one basic creative idea and no matter how he is driven off, you will find that he always comes back to it until he has a chance to prove it in purity, or die with the idea unrealized." — Frederick Kiesler
They do not walk, they drip down the surface of the pictures, they are raindrops leaving an erratic trail, drifting down the paper, as described by Asger Jorn and Guy Debord in their psychogeographies.