Windows, Curves, and Painting with Sunlight
Research notebook · October 11, 2026 · Demonstrated printed glass and computational caustic optics; proposed printed windows, stained glass, sunlight art, and freeform rooms.
Most of the shapes in an ordinary house come from how the parts are made and delivered: rectangular windows, flat sheets of wallboard, square corners. A printed house can ask what shape each surface should be, then make that shape. This page collects the evidence and the limits.
Glass can be printed
MIT’s Mediated Matter group developed G3DP, an additive-manufacturing platform for optically transparent glass using a heated kiln cartridge, a ceramic nozzle, and an annealing chamber. Its successor, G3DP2, added integrated thermal control and four-axis motion and printed three-meter glass columns for Milan Design Week in 2017. The group notes that varying form, transparency, and color can control how light is transmitted, reflected, and refracted.
These are exhibition and research pieces, not certified windows. A building window must also meet requirements for heat loss, solar gain, condensation, impact and breakage behavior, air and water tightness, and, in some rooms, emergency escape. Thermal stress during cooling, which annealing addresses, becomes harder as pieces get larger and more complex. The demonstrations establish that printed glass can be transparent and architectural in scale; they do not establish that printed glazing performs like a manufactured insulated window.
Any shape of window
If the window region is printed with the wall, its outline need not be rectangular. The constraints become performance rather than catalog: how much glass area the room needs for light and heat balance, how loads route around the opening, and whether an opening section is required for air or escape. An odd outline that is fixed glass is the easiest case. A moving, sealing part in an unusual shape is harder and should probably remain a replaceable cartridge.
Stained glass, again
Coloring glass with metal oxides is ancient. What made stained glass rare in ordinary houses is the labor of cutting, leading, and fitting. The proposal is to vary glass composition locally during printing so color regions are built in. Open questions: how sharply color boundaries can be controlled in a molten or sintered process, whether colored regions have different thermal expansion and need graded borders (see graded transitions), and how colored regions affect solar heat gain.
Windows that paint with sunlight
Caustics are concentrated light patterns formed by refraction or reflection, like the bright lines on the bottom of a swimming pool. EPFL’s computational caustics research, including Schwartzburg, Testuz, Tagliasacchi, and Pauly’s High-contrast Computational Caustic Design (SIGGRAPH 2014), shows how to compute the surface of a transparent or reflective object so the light it redirects forms a chosen image on a receiving surface. The spinoff Rayform produces such pieces and states that any small, sharp source, including the sun, can be used; it notes acrylic is easiest to shape, while glass can be cast or blown into a mold. EPFL’s sol.id installation used mirror-like metal plates to form portraits in sunlight as the sun moves.
The proposal for the house: design a window, or a panel within one, so that direct sun at a chosen date and time draws an image on a chosen spot of floor or wall. Because the sun’s position for a site is computable for any moment, the design target can be a specific afternoon, a seasonal event such as a solstice, or a daily window of time. Things to work out:
- Timing and drift. The image will move with the sun and be sharp only near its design moment; how long is it recognizable?
- Weather. Overcast skies produce diffuse light and no image.
- Size and resolution. Image size depends on the optic’s dimensions and the distance to the receiving surface; precision of the printed surface limits detail.
- Glare and heat. Optics that focus light also concentrate heat. Check every sun position through the year for glare and hot spots on furniture, floors, and people.
- Coexistence. Can a caustic panel be part of an insulated window, or must it be a separate interior pane?
Curved walls and rounded corners
A printer’s tool path does not care much whether a wall is straight. Curves, rounded corners, vaults, and shallow domes therefore cost mostly design effort rather than special materials. Rounded inside corners are easier to clean; rounded outside corners are kinder to people who bump into them. Limits: most furniture and appliances assume flat walls and square corners; curved display surfaces need image correction; and curvature changes structural behavior, sometimes helpfully (shells and arches carry load well) and sometimes not (local stress concentrations, harder inspection).
A useful first experiment
Print or cast a small caustic test panel designed for a known sun position at the test site, alongside an unpatterned control. Photograph the receiving surface at intervals across the design day and on days before and after. Measure the peak surface temperature under the brightest focal region. Separately, print a small glass coupon with two color regions and a graded border, and inspect it for cracking after thermal cycling.
Related pages: lighting and displays, printed glass channels, walls that move and speak, and the development path.