The commission for these four was a single sentence: "four sites of your own choosing — a particle effect always wows me." Everything else — subjects, palettes, typography, techniques — was Claude Fable 5's call, executed through the same discipline as the rest of the series (briefs first, three critique passes, accessibility floor, zero console errors). The base method is in the Fable Fifteen guide; here's what's specific to these four.
The showpiece is a hand-rolled GPGPU system — no particle library. Positions and velocities live in floating-point textures ping-ponged between framebuffers; the velocity shader adds curl noise, a spring toward the current morph target, a cursor gravity well, and a supernova impulse on section changes. Six morph targets are baked by sampling drawings and star catalogs into position textures (Orion uses real right-ascension/declination). Fast particles blue-shift — the point shader reads the velocity texture for a Doppler shimmer. An FPS governor walks resolution from 512² (262,144 particles) down to 128² on weak GPUs; reduced-motion gets a still render; no-WebGL2 gets a 4,000- particle 2D canvas. The lesson: a wow that doesn't degrade gracefully is a bug report.
The remaining picks share one idea: the interface teaches something true. Halvard Forge's tempering bench maps the real oxide colors (straw at 205° through blue at 300°) against the real hardness/toughness trade-off, and its damascus visualization folds actual layer math — 2 to 256 in seven folds. Quoin & Vellum's endpapers run a genuine marbling simulation (sequential ink-drop displacement plus tine-comb rakes, computed by per-pixel inverse mapping) seeded from each lot's catalogue number. Piste Club's bowl is parametric geometry with the true 42° banking, riders lapping at real speeds, and a lap calculator that does honest arithmetic. Delight that's also correct outlives delight that's only loud.
One site uses generated media: the forge's breathing-ember hero, a 2K still animated into a 5-second cinemagraph with Higgsfield's Kling 3.0, compressed to under 500 KB, muted, looping, poster-backed, paused offscreen, and replaced by the still under reduced motion. The other three are entirely procedural — the particles, the marbling, and the velodrome weigh ~250 KB of code combined.
The passes still caught real bugs here: a damascus renderer that collapsed to grey at high fold counts, additive blending that turned the particle face into a salt pile, a no-JS hero stuck at opacity 0, and a Roman-numeral catalogue number that contradicted the house's founding date. "Looks done" is not done — that's the whole method.