The whole idea is to make a surface that *remembers* light, then draw on it with a beam instead of a pen. Cast a slab of phosphor-loaded silicone, mount a UV laser diode where the pen normally goes on the AxiDraw, and run a plot - wherever the beam dwells the powder excites and holds, so the linework blooms back as a glowing afterimage once the room goes dark. Simple to say. The two halves - the casting and the plotting - each have a floor you fall through if you guess at the numbers.
Getting the pour to settle flat
The tiles only read if the top is dead flat and the powder is evenly suspended - any meniscus or settling shows up later as a bright rim or a dim corner once you charge it. Two things fixed it: a shallow frame mold so the pour is wide and thin rather than deep, and folding the phosphor into the part-B base *before* adding part-A so the powder wets out before the clock starts.
- 01Disperse the glow powder into the part-B silicone first and mix to a uniform slurry - it wets slowly, and if you wait until after catalyzing you will not have time.
- 02Add part-A, mix, then degas under vacuum. Platinum silicone tolerates it and the trapped air is what otherwise floats powder to the surface as a speckled skin.
- 03Pour into a shallow 3D-printed frame on a leveled bench. Wide and thin beats deep - depth just buries phosphor the beam never reaches.
- 04Skim the surface with a card once, then leave it. Overworking the top reintroduces bubbles right where you most want clarity.
The laser is not a pen
The plotter wants to drive the head like it is inking: full speed on the draw, pen-up between paths. But charge is a function of dwell - how long the beam sits on a spot - not just whether the path was traced. Run it at normal pen speed and the lines barely take; the phosphor needs the beam to linger. So the real variable is feed rate, and it trades directly against line brightness.
- 01Slow the draw feed *way* down from ink speeds - the beam has to dwell long enough to pump the phosphor, not just pass over it.
- 02Force pen-up between every path so the laser is gated off in transit. A laser does not stop drawing when it lifts a couple millimeters the way a pen does - it has to be switched.
- 03Keep the focal distance constant. The frame holds the tile, but a warped slab drifts out of focus mid-plot and the line goes soft.
- 04Charge in the dark and photograph immediately - the afterimage starts decaying the moment the beam moves on.
What it looks like in the dark
When it works, the plotted paths - grids, contour fields, warped meshes - bloom back out of the slab in orange, teal, and blue, fading slowly as the charge decays. The decay is the point, not a bug: the drawing has a half-life, so the same tile reads differently thirty seconds after you kill the lights than it does at the instant the plot finishes.
It is the only drawing I make that erases itself while you watch it.
Open questions
Still unresolved: the brightest paths and the dimmest ones decay at noticeably different rates, so a dense plot goes muddy before a sparse one even dims. I think that is a dwell-uniformity problem - the path-ordering matters because retracing near a still-glowing line double-charges it. Next test is plotting hot regions last so they finish brightest, and measuring decay with a long exposure instead of my eyes. Will update.
