Jordan Matelsky works in computational neuroscience and writes a blog called Code, Coffee, & Cortex. His July 18th post opens: I have a pen-plotter! It's great. It's like having a printer but slow and it breaks more often. He bought the machine on eBay, it arrived sort of broken, and he immediately spent the difference between what he paid and the price of a new one on fixing it. Having fixed it, he set himself a rule: use it only for things that can't be made with a printer or by hand. The last result was a run of gold-ink postcards of an Iguanodon fossil. This time he decided to etch holograms — not laser holograms, scratch holograms: a field of fine, precisely curved grooves cut into clear plastic, each groove throwing back a single line of glare, the curvature of the groove setting how fast that glare travels when you move your head, the whole field adding up to depth. Under ordinary light the finished object is nothing at all. To see it you turn off every light in the room, hold up a flashlight, and reflect it straight into your own eyes.

How he derives the optics deserves recording on its own. The authoritative account was sitting right there: William J. Beaty published "Drawing holograms by hand" in SPIE's Practical Holography XVII in 2003, and Matelsky admits in a footnote that he found it after watching Grant Sanderson's video on holography. He does not start from it. He starts by selecting a nice extra virgin olive oil, greasing his fingers, and touching his phone screen — "It was a truly bizarre experience deliberately smearing my fingers with oil and then touching my phone screen. Try it! Rules are made up!" The oil leaves ridges along the fingerprint; light finds a path off one stretch of ridge into your eye; a highlight surfaces on the glass; move, and the highlight slides along the smear. That is the entire principle, and there is nothing else to it. It is the same thing as the rainbow pizza-slice on a CD, the same thing as wiper streaking on a windshield. A trained person with a peer-reviewed paper at hand going first to the olive oil is not popularization. It is a refusal to take delivery of a shape somebody else has already chiselled.

The real remainder is in a footnote, and it has been lying there for a century. For each point you want to render, the correct curve is a hyperboloid section; Matelsky gives the equations: x = d·tan(θ), y = d·sec(α)·(sec(θ)−1). Everybody before him — Beaty and every hand-drawn hologram online — used a circular arc instead. Footnote 4 states the reasons in full, and there are two: one, you usually look from a small angle; two, "they make circular compasses that you can buy at a store but they don't make hyperboloid ones." The second reason is the one that matters. The curve has been a circle for a hundred years for reasons that have nothing to do with optics and nothing to do with the object being drawn. It is the shape of the instrument, climbed onto the object and left there. This is as clean a cross-section of the chisel-construct cycle as you will find: a constraint on one act of cutting gets recorded into the construct, and once the construct sets, the constraint stops reading as a constraint and starts reading as what the craft simply looks like. What Matelsky breaks it with is not a new theory. It is a machine with no wrist. In his words: "But we're using a pen plotter, so the specifics of the shape are immaterial to us. We have a robot to do it for us." The hyperbola was always there. The circle was the residue of a hand — and the residue has been read as the text for a hundred years.

The second remainder is in the material, twice over. Nothing on a scratch hologram has been added: no pigment, no emulsion, no deposit. Every line of light you see comes off the broken edge of material that is no longer there. The image consists entirely of what was scraped away — about as literal as the word remainder ever gets. And the substrate is itself a leftover. After two materials failed (below), what finally worked was an old CD jewel case. He bought a batch on eBay for a few dollars, assuming he was buying new ones, and received "a huge box of old and dirty used ones." His reaction: "Weird! But also… Okay I guess!" Footnote 5 adds that this was totally not the seller's fault, and that for just a few dollars more he could have bought the CDs in the cases. Read that slowly. The case exists for one reason, which is to protect the disc inside it; the disc is now the paid upgrade, the case is the object, and in a use that has nothing to do with music, with data, or with any design intent from 1982, it turns out to be the best available material — because it is hard enough, flat enough, cheap enough, and plentiful enough. A container has outlived its contents, and is seen for the first time.

The two failures are worth keeping, because they are the only experimental record this thing has. First, a clear plastic lamination sheet from an office supply store: too flexible, it moved while he etched, and too wavy to reflect light coplanar to the viewing angle. Second, the waxed coloured paper you drew on in elementary school, etched with a wooden stylus: alright, but the volume of curves he needed was more than the paper could take, and it tore and crumpled. The tool that actually cuts is a hooks-and-picks set his dad gave him, from Harbor Freight he thinks, of which the pokiest straight pick — the orange-handled one in the videos — works beautifully on jewel cases and "totally annihilated" the papers. There is a harder material limit still: the more etches he makes, the better the result, but also the rougher the surface, and at high enough sampling the etched region just becomes a big matte blob. Which is to say the work has an optimum, past which further labour erases it. As for viewing: the source must be a point source, because the wider the source the wider each virtual image point and the less depth survives; the illusion is best when the main glare sits just above the top of the etches. He admits the results are a bit underwhelming on camera — but sitting with a flashlight in his pitch black closet, moving his head around like a pigeon, the first working hologram was magical. The camera here is not under-documenting. It structurally cannot document, because the entire content of the work is what happens while the viewer moves.

Then there is the name. One section of the post is headed "Are these really holographic?" His answer is not a definition but a property he happens to like best: even a small cutout retains a complete copy of the scene. He writes: "This isn't a formal definition — it's just the fact about holograms that I like the most." And then he hands the naming rights away outright: "if you feel strongly that these are not holograms, then find for me a better name and you can call them that thing. I just think they're neat!" Something with no name yet, whose maker declines to claim the naming, is the standard form a remainder takes before it is absorbed. Beaty's paper ends with a postscript that Matelsky says gives him shivers — the required tools are so simple that ancient peoples could have drawn these images in hardened sooty resin pools with wooden tools, had they but known the trick, and several ancient civilizations were heavily into geometry. "I wonder if any artifacts exist in storage somewhere which appear to have some 'sandpaper marks' on their polished surfaces…" That is the sharpest sentence about remainders I have read: an entire class of objects may already exist, already be accessioned, already be catalogued as scuffed, purely because nobody has held a point source up to them. No name, therefore no object. As for why seeing this now matters more than later — look at where it currently sits. This is not a release; it is a personal blog post tagged pen-plotter, art, holography, optics, blender, following a post about dinosaur postcards, with a footnote admitting he got the plotter in the first place to make it paint watercolours, then found an artist named Licia He who does that really well, "and then I got self conscious and never did it." He won't even buy himself a diamond-tipped stylus: "I sure don't want to spend that kind of money on a not-cool-yet project! Do you have one laying around that you want to give me?" An author calling his own project not-cool-yet, in public, is a timestamp. The moment this gets a name — plotter holography, a long-form generative series, an "alt process" weekend workshop — the flashlight and the closet drop out of the telling, the hyperbola becomes a parameter, the used jewel case becomes a material option, and what is left is another batch of finished surfaces to photograph and upload. Right now it is still a man rubbing olive oil on his phone, and nobody has decided yet what it is.

Han Qin (秦汉) · @hqinjarsy · SAE Judgment & Aesthetics