# The Chamber as a Volume — acrylic stack spec & depth design

A backlit, six-plane physical piece for the eufyMake E1: three acrylic sheets,
printed front **and** back, spaced with air gaps over an LED panel. This is
roadmap Phase 3 made literal — the scene model's per-track `z` and `age` stop
being opacity tricks and become actual millimetres.

## Physical stack (proposed — buy list at bottom)

```
viewer
  ─ C-front   the hand: grease pencil, réseau, fiducials, header, scratches
  ═ sheet C   3 mm clear cast acrylic
  ─ C-back    near scatter: δ-ray curls, close cosmics
      ~6 mm air gap
  ─ B-front   THE EVENT: sharp beaded track cores
  ═ sheet B   3 mm
  ─ B-back    halation: the same tracks, blurred — real glow-behind-the-line
      ~6 mm air gap
  ─ A-front   history: older background events, sinking
  ═ sheet A   3 mm
  ─ A-back    the cause: pressure disk (CMYK-only → pure glow) + chamber optics
      ~12 mm gap
  ▤ diffuser  frosted acrylic 2–3 mm (kills LED hotspots)
  ▦ LED panel A3 slim light pad
```

Plane depths (A-back = 0): 0 / 3 / 9 / 12 / 18 / 21 mm — two depth scales:
3 mm *within* a sheet (fine parallax: halation, moiré) and 9 mm *between*
sheets (coarse parallax: cause → event → hand).

**The depth story is causal, not just spatial**: deepest plane is the cause
(the pressure wave, pure transmitted light), then history, then the halation,
then the event itself, then the debris flying toward you, and finally — on the
front glass, where scanners actually wrote — the human hand measuring it all.
Parallax reads as *interpretation floating above evidence*.

## Sheet & print geometry

- Sheet: 330 × 420 mm (E1 full bed, A3+), portrait. 3 mm clear cast acrylic,
  gloss both faces.
- Art square: 300 × 300 mm, centred horizontally (15 mm margins), top edge at
  y = 20 mm. Zone below (y = 320–420) carries film furniture / data box /
  caption on C-front only; other sheets stay clear there (light spills through
  — the plate floats in a lit void).
- Corner mounting holes 5 mm ∅ at 8 mm insets, all sheets + diffuser, for M4
  nylon standoffs (3 mm + 6 mm + 6 mm spacer stacking, or threaded rod with
  nuts as spacers).
- Registration: every plane file carries corner crosses at the same four
  coordinates just outside the art square; back-face files are **mirrored** at
  export so they read correctly through the sheet.

## White-ink logic (backlit grammar)

| zone | channels | lit result |
|---|---|---|
| clear acrylic | none | pure light |
| glow elements (disk, halation, deep tracks) | CMYK only | stained-glass — light pours through colour |
| focal ink (event cores, grease pencil, furniture) | CMYK + white underlay | holds density against the panel — reads as ink |
| blocking (none in v1) | white + black | opaque |

Rule of thumb: **depth = transparency**. The deeper the plane, the less white
ink; the front glass is the most "solid" ink. The disk gets *zero* white — lit,
it becomes a light source (the laser-interference reference lives here, later).

## Pipeline

```
plan (fable/stack/plans/*.mjs)
  → node tools/stack-render.mjs <plan>          per-plane SVGs + manifest.json
  → fable/stack/simulator.html?c=<id>           parallax + backlight art-direction
  → [next] tools/stack-export.mjs               print masters: mirrored backs,
                                                white-ink masks, A3 layout @ true scale
```

`src/render/stack.js` splits one generated scene into per-plane sub-scenes
(selectors: track kind / z band / age band; disk, optics, damage, media,
fiducials, header as flags) and renders each through the untouched `renderSVG`
with `transparentPaper`. Bloom/core pairs use the *same* track selector so
bubble positions are identical on both faces (same filtered list → same salted
draws) — keep `density`/`size` equal within a pair.

Per-plane renders set `depth`/`aging` low: the physical stack now *is* the
depth model; double-encoding it as opacity would fight the medium.

## Calibration coupon (print before the hero)

One A5 sheet, double-sided: white-ink step wedge (0/25/50/75/100%, single +
double pass) · the same δ-ray at three white levels · CMYK-only vs CMYK+white
swatch pair · front/back registration cross · 6 pt / 8 pt mono type both faces.
Judge **lit on the panel**, not in hand.

## Buy list (if starting from zero)

- 3× cast clear acrylic 330 × 420 × 3 mm (+1 spare), protective film both sides
- 1× frosted/opal acrylic 330 × 420 × 2–3 mm (diffuser)
- A3 slim LED light panel (dimmable if possible)
- M4 nylon standoff kit (assorted 3/6/12 mm) or 4× M4 threaded rod + nuts
- IPA + lint-free cloths; adhesion promoter if the E1 profile recommends it