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?
Kasuri is thus a textile that appears to have been rubbed. Since the edges of the pattern do not align, they take on the nature of an odd number rather than an even number. Without this rubbing or smudging, kasuri could never have been. However, since it is precisely this misalignment and blurry effect that is the source of kasuri’s beauty, we are presented with an interesting problem. I will call this problem ‘the beauty of odd numbers’.
The beauty of kasuri is received as a gift. As long as the laws of nature are upheld, the beauty of kasuri remains intact. This demonstrates the curious principle that the artisan is deprived of technical freedom but works in the freedom of nature.
In this sense, kasuri can be said to be created in a state of freedomless freedom.