Copperplate Engraving — our demo

One example among many. Don't reuse its story, arc, shots, props or timings.

Demo: The Honeybee, Plate VII (40.0 s) · engraving.mp4 · source in demo/ · all words from demo/content.json

Story & structure

A scene demo, not a story: a museum object label for the screen next to a case. One object (the honeybee), its name, three things you did not know about it, and where to see the real one ("see the living hive in Gallery 4").

Structure (40 s): copper ECU → proof pulled → pull out to the plate → three magnified details (eye, hamuli, corbicula), each flying to its slot → silence → hand colouring → locked final plate → tissue-guard end card.

How the native moves served information in this demo:

• The cut itself was the hook: the first frame is the burin mid-stroke in copper, curl of copper rising ahead of the point. Nothing else is on screen, so the eye has one place to go.
• The build (outline → first hatching → cross-hatching → darks and hair) was the "this is a serious, made thing" beat, kept under 5 s and under the title.
• The magnification roundel was the information carrier: a ring is scribed around the part, the inside is burnished clean and re-engraved at magnification, and the roundel flies to its slot trailing a leader line. The viewer sees where the detail is and what it looks like in one move. Its label (roman capitals, italic term, script note) is engraved when it lands.
• Hand colouring was the climax, after a real silence and after all information is on the plate, so it read as reward, not as new information.
• The final plate was the poster: every label, the call to action and the engravers' credits at once, locked off.

Use cases, with a shot structure for each (examples, not recipes):

Shots

The camera is a loupe over the plate. Beat by beat in the demo:

Motion timings in this demo: the first line is one stroke followed by the camera, 5.4 s long, so at frame 0 it is already a third cut; strokes run 6–90 at once; roundels lift 30 px at mid-flight and grow to radius 120; colour regions bloom over 1.25–1.6 s each and start 0.42 s apart.

Score structure

Three layers: room tone (a quiet workroom with a faint clock on copper; paper room after), foley keyed to picture events, and a baroque chamber score.

• Score: harpsichord + string quartet, 96 BPM, D major. music/score.py reads events.json: each detail section (A long / B tilt / C pull-back) is written once and placed where the film puts it; the outro shifts with the end of the details, so any number of details gets a matching score. Under narration the melody sits an octave up, out of the voice's band. Engraving sections are all pizzicato (the burin's small precise cuts), density growing pass by pass; each roundel = a high "ting" as the ring is scribed, a rising line as it flies, a low pizz as it lands. Before the colour: a run that stops dead, then true silence (1.25 s). The colour is the first time the strings use the bow. The final plate lands on a V–I cadence.
• Silences: 2.0–2.5 s (burin lifted, before the press thump and the downbeat) and 25.0–26.25 s (before the first drop of water).
• Foley as built: burin = band-passed hiss (2.6–9 kHz) with chatter clicks and a faint plate resonance (1.18/2.31/3.47 kHz); swarf = tiny 5–9 kHz pings; lift = metallic tick; press = low roller rumble (J-cut 0.35 s early) and a thump; peel = dense paper crackle; hatching = granular micro-scratches whose density rises with each pass; ring = circular scribe; burnish = soft rub; roundel flight = paper whoosh; landing = paper tap; letters = dotted ticks; notes = pen scratch at ~4 Hz strokes; colour = a falling water "plip" then a wet brush swish per region; end card = tissue rustle (J-cut).
• Narrator: Kokoro bm_fable (en-gb), speed 0.92, a gentle naturalist; music ducked to ~50 % under him (the bowed strings duck least).

Score form, bar by bar

Original, written in code (music/score.py, deterministic: a rebuild gives a byte-identical score.wav); no existing or public-domain tunes. Key D major, 96 BPM in 4/4 (beat 0.625 s, bar 2.5 s, 16 bars = 40.0 s). Forces: harpsichord (continuo and solo figures) and a string quartet (solo violin I, ensemble violin II, violas, cellos, contrabass); the strings play pizzicato up to 25.0 s and use the bow only from 26.25 s. Rebuild from the repo root with .venv/bin/python styles/engraving/demo/music/score.py (about 5 s; writes score.wav, stems/, cues.json, CREDITS_music.txt). Level −18.0 LUFS integrated (BS.1770), peak −1.2 dBFS, 48 kHz stereo 24-bit. Stems harpsichord.wav, pizz.wav, bowed.wav (40.0 s each, same gain as the mix, so they sum to the mix before the limiter, about 1 dB of peak limiting on two hits).

The form is a trio-sonata texture: the grammar of engraving, then colour. Times are for the demo's three details.

Narration windows. Inside 6.4–9.6, 9.8–14.9, 15.3–19.2 and 19.7–23.3 the pizz is short and dry, which keeps 300 Hz–3 kHz transient rather than sustained. During 26.9–30.9 the bowed chords sit mostly in the bass (cellos and contrabass below 300 Hz) and above 900 Hz (violins at A5–D6), with only violas and violin II in the voice band at pp. The harpsichord plays only four soft broken chords there.

Reverb. S.room per stem, applied before the silence gates, so no tail leaks into 25.0–26.25: harpsichord size .28 / mix .16, pizz .30 / .18, bowed .42 / .24. A 35 Hz high-pass on every stem.

Timing check. Each accent in music/cues.json is measured on its own rendered stem, after reverb: the first 30 % rise from the local trough to the local peak in [t − 60 ms, t + 120 ms]; low landings measured below 300 Hz, tings above 2 kHz; tolerance ±42 ms (one frame at 24 fps). For the bowed entry, the first bowed sample above −100 dBFS.

Palette & props

The sheet: 1920×1080 world units, laid paper #f1e8d2, world-space paper texture (fibres, laid lines, sparse foxing #9a6a34). Plate mark (the pressed, bevelled rectangle) at (70, 44)–(1850, 1036): plate tone #e8ddc2 at 55 % inside; bevel dark on the top/left walls, light on bottom/right (light from the upper left). Ruled border: 2.4 px rule + 0.8 px hairline 9 px inside, (100, 72)–(1820, 1008).

Ink: #1c1510. World line widths at 1× zoom: outlines 1.8–2.4 (swelling ×0.45–1.35), first hatching 0.18–2.0, cross-hatching ×0.78, third family ×0.6, hair and stipple 0.6–0.9. Hatch spacing on a 600-px figure: 3.1–3.7 px (first), ×1.1 (cross), ×1.25 (third). Hatch thresholds on a 0–1 tone: first family from 0.14, crossing from 0.46–0.5, third from 0.74–0.78.

Light: {x: −0.55, y: −0.62, z: 0.56}.

Lettering: Bodoni Moda (title 50 px, tracking 0.16; labels 17 px, tracking 0.14), italics for Latin (20–24 px), Pinyon Script for notes (29 px). Subtitles: Pinyon Script 38 px, #2b1e14, on a deckled paper slip (#f4eddb, soft shadow) at the bottom centre, max width 860, up to two lines; on 0.1 s before the line, off 0.6 s after it; never over the call to action.

Roundels: radius 120, double rule (2 px + 0.75 px, 4 px inside), ruled ground of horizontal lines every 11 local units; content drawn for a 500-unit radius and scaled in. Slots in order: upper left (300, 300), lower left (300, 700), lower right (1620, 700), upper right (1620, 300). An unused slot shows the specimen at natural size (plate ≈ 20 cm wide, so a 13 mm bee is 0.19× the main figure).

Leaders: 0.95 px, from a dot on the part to the roundel's rim, routed around wings and body with ≥ 34 px clearance (one waypoint), a small italic figure number near the root.

Hand colouring: abdomen amber #d9962a, thorax ochre #a8743e, head #8a6242, eyes #6e4a3c, wings pale blue-grey #a9c3cf (alpha 0.5), legs #7a5a3c, pollen #eaa21a (alpha 0.95). Multiply over paper; 3.5 px spill, 2/1.5 px misregister, tide-line at the wet edge, low-frequency density lift (0.55), 1–2 backruns in large regions, granulation.

The copper (opening only): base #5e2a12 → #94502c → #4e220e, a swirl of polishing hairlines (overlay), a soft studio window reflected across the plate (four panes, blurred 14 px, over a 90 px room glow), dark room toward the frame edges. Grooves: dark trough #240c05, a bright burr rgba(255,226,186) offset toward the light, a warm glint on the far wall. Burin: lit face #d9e0e6, shadow face #262b30, sharp ridge highlight, brass ferrule, mushroom-shaped wooden handle with grain; turned 0.22 rad (≤ 15°); swarf a thin, narrowing copper ribbon curling irregularly (turns open out as it grows, an occasional twist).

Subjects: the honeybee (subjects/bee.js) with three drawn magnifications — compound eye, hamuli (wing hooks), corbicula (pollen basket) — in subjects/details.js; a second built-in subject, the great scallop (subjects/scallop.js), used by content_alt.json.

End card

The title is part of the plate (engraved, not a separate card). End card: a translucent tissue guard falls over the plate; on it, engraved: film title, style name, LEMO-OPUSCAR, LemoLab × Claude Opus 5.5, three credit lines. The "LemoLab × Claude Opus 5.5" sign-off belongs to this library's demo only; a user's film carries no LemoLab credit and no copy of this card.

Build notes

sh styles/engraving/demo/build.sh              # voice → check → score → events → mix → cue check → srt → frames → mux → stills

• demo/engine/: burin.js (lines), plate.js (sheet, lettering, roundels), wash.js (colour), copper.js (copper, burin, swarf), index.js (public entry + engraveShape).
• demo/subjects/: bee.js, details.js (eye, hamuli, corbicula roundel drawings), scallop.js (second built-in subject).
• demo/film.js: timeline (96 BPM grid), camera, render; reads content.json. demo/mix.py: foley + voice + ducked stems. demo/music/score.py: the score, written against the cue map of picture events (bar-by-bar form under Score structure). demo/tools/cuecheck.py: score accents vs picture events (all within 1 frame) and the silence level.
• Render with core/render/video.mjs --workers 2; frames take 60–500 ms (copper and colour frames are the slowest).

Pitfalls tied to this demo's props:

• Wing veins must close their cells. Random vein strokes look fake; define long veins as curves and snap cross-veins onto them (bee.js, FX).
• Leg joints drawn as full capsules look like beads. Exclude the previous segment so only the distal cap shows.
• Two renders of the same demo folder collide: video.mjs writes its segments to <demo>/out/, so render the main and alt films one after the other.
• Burin skew: keep it at 0.22 rad; 30° reads as poking beside the line.
• Leaders hugging a wing read as crossing it: route them with ≥ 34 px clearance.
• "Apis mellifera": Kokoro says it acceptably but whisper can't transcribe it; the line uses the asr field.

content.json fields

demo/content.json drives every word, number and colour.

Steps: edit (or copy) the JSON → sh styles/engraving/demo/build.sh my_content.json (TTS + whisper check, events, score re-placed from the events, mix, cue check, subtitles, frames). To keep the main film untouched, sh styles/engraving/demo/tools/build_alt.sh my_content.json builds everything in demo/out/alt/ instead (the demo's content_alt.json, 2 details, 35.6 s, passes the cue check).

Minimal example:

{
  "title": "The Great Scallop", "latin": "Pecten maximus", "plate_no": "Pl. XII",
  "series": "Shore Gallery · Shells of the Atlantic Coast", "subject": "scallop",
  "details": [ { "name": "Hinge", "latin": "umbo", "note": "The oldest part of the shell.", "focus": "umbo" } ],
  "colors": [ { "region": "shell", "color": "#d98a5c" }, { "region": "bands", "color": "#a8423a" } ],
  "caption": "Hold a real shell at the Discovery Table",
  "voice": { "voice": "bm_fable", "speed": 0.92, "lines": [ { "id": "title", "text": "Plate twelve. The great scallop." } ] }
}

Swapping this file and running build.sh checks that the engine re-flows; it is not how a user's film is made.

Engine reference

import { B, engraveShape, Wash, drawSheet, engraveText } from './engine/index.js';

// 1. any shape + a light direction → an engraved figure (contour lines follow the form), cut in order
const { ink, shape: spark } = engraveShape(
  'M0 -120 C12 -40 40 -12 120 0 C40 12 12 40 0 120 C-12 40 -40 12 -120 0 C-40 -12 -12 -40 0 -120 Z',  // a four-pointed spark
  { at: B.xf(860, 560, 1.9), light: [-0.6, -0.7], spacing: 4.2, style: 'contour' });               // or style: 'hatch'
engraveShape('M0 0 H150 V26 H0 Z', { at: B.xf(1140, 740, 1), ink, g: 't' });                        // its cursor tail, same ink
ink.schedule(['ol', 'tol'], 0, 1.1, { conc: 2 }); ink.schedule(['h1', 'th1'], 0.8, 2.2, { conc: 40 });
ink.schedule(['h2', 'th2'], 1.6, 2.7, { conc: 40 }); ink.schedule(['h3', 'th3'], 2.2, 3.0, { conc: 40 }); ink.build();

// 2. the "only colour": hand-colour one element and leave everything else in black ink
const w = new Wash({ scale: 1.5 });
w.add({ path: spark.path, polys: spark.polys, color: '#D97757', origin: [860, 560], t0: 3.0, dur: 1.2, alpha: 0.85 });

window.render = t => {
  drawSheet(ctx);                 // paper, plate tone, plate mark
  w.draw(ctx, t);                 // colour under the ink (omit for pure black-and-white)
  ink.draw(ctx, t);               // everything cut by time t; lines being cut grow
  engraveText(ctx, 'THE SPARK.', 960, 170, { size: 50, weight: 600, track: 0.16, p: t - 1.5 });
};

Runnable as demo/example/index.html (node core/render/still.mjs styles/engraving/demo/example 4.5), output in demo/stills/engine_example.jpg.

Main functions:

A minimal runnable example of the whole thing is demo/film.js with content_alt.json (a different subject, two details).