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?
Sitting there in the Whitney's coffee shop, Irwin pointed through the glass wall up at the play of shadows on a building facade across the street. "That the light strikes a certain wall at a particular time of day in a particular way and it's beautiful," he commented, "that, as far as I'm concerned, now fits all my criteria for art."
At the terminus of Irwin's trajectory, when all the nonessentials had been stripped away, came the core assertion that aesthetic perception itself was the pure subject of art. Art existed not in objects but in a way of seeing.