What the loom does
Cloth is two sets of threads crossing at right angles. The warp runs lengthwise and is stretched on the loom. The weft is carried across by the shuttle, one pass (a pick) at a time. Before each pick some warp threads are raised and the rest stay down. The gap between them is the shed, and the shuttle flies through it. Where a warp thread was raised, it lies on top of that pick and you see warp. Where it stayed down, you see weft. A whole picture is nothing more than this up-or-down choice, made for every warp thread on every pick.
Simple looms group the warp onto a handful of shafts, so only a few patterns are possible. Jacquard's machine gave every warp thread (or every thread in a repeat) its own hook. A chain of punched cards chose the hooks: one card per pick, one hole position per hook. A hole lets the hook be lifted; no hole pushes it aside. This followed earlier work by Basile Bouchon (punched paper, 1725), Jean-Baptiste Falcon (cards, 1728) and Jacques de Vaucanson (a cylinder mechanism, 1745).
Inside the head
Each hook hangs through the eye of a horizontal needle, and a spring pushes the needle toward the card. A square cylinder (the prism) presses the next card against the needle tips. Where the card has a hole, the needle slips in and its hook stays upright over a blade of the griffe. Where there is no hole, the card pushes the needle back, and the needle nudges its hook off the blade. Then the griffe rises and lifts only the hooks still standing on it. Cords pull those warp threads up, the shuttle passes, the reed beats the new pick into the cloth, the griffe drops, and the prism turns to the next card.
Weaves: plain, twill, satin
The rhythm of over and under is the weave structure. Plain weave alternates every thread: firm, with no floats. In a twill the interlacings step one thread per pick, so the cloth shows diagonal ribs (denim, tweed). A satin spreads its interlacings so far apart that they don't touch, and one set of threads floats over many others. That gives the smooth, shiny face of satin. Long floats look glossy but snag easily, so the page measures the longest float on both sides of the cloth.
Pictures from structures
The designer paints on point paper (mise-en-carte): one square per hook and per row. Each colour on the paper does not stand for a thread colour. It stands for an effect: which weft comes to the face and in what structure. In damask a warp-faced satin figure sits on a weft-faced satin ground, the same threads both ways round, so the picture appears and disappears as the light moves. In shaded weaving, satins with 1/8 to 7/8 of the warp showing act as grey levels. In 1839 Michel-Marie Carquillat wove a portrait of Jacquard this way, using about 24,000 cards. Charles Babbage hung a copy in his drawing room.
More colours: extra wefts
The warp is fixed for the whole cloth, so extra colours come from extra wefts. With three wefts every design row takes three picks. Each weft comes to the face only where the design wants its colour and spends the rest of the row floating at the back. Those back floats must be tied down every few ends, and the tiny tie points show on the face as specks. Turn the binding off and the back turns into long loops, the price of a brocade.
Cards and computing
We may say most aptly that the Analytical Engine weaves algebraical patterns just as the Jacquard-loom weaves flowers and leaves. — Ada Lovelace, 1843
Babbage planned to feed his Analytical Engine with Jacquard-style cards. Herman Hollerith's punched cards counted the 1890 US census, and cards carried programs for most of the 20th century. A Jacquard card is a row of bits, and the card chain is a program with one instruction per pick. You can export it here as a WIF file (weaving information file) that hand-weaving software can read.
Keys: Space weave/pause · → one pick · End weave all · Home rewind · B back/face · F fit · L linen tester · S sound · Ctrl/⌘ Z undo painting.
What is modelled and what is simplified
- Exact: the lift logic. Point paper → effects → card holes → hooks → harness tie (straight or point) → warp up or down for every end and pick. The back of the cloth is the face inverted and mirrored, and float lengths are counted on both sides.
- Weave structures are the standard ones: plain, basket, ribs, twills, herringbone, 5- and 8-end satins (counters 2 and 3), and a shaded 8-end satin series.
- Multi-weft cloth is a simplified compound weave: the face weft uses its structure, the hidden wefts are tied by a sparse satin. Real lampas and brocades often use a separate binding warp.
- WIF export writes Jacquard as one shaft per hook with threading and liftplan. It follows the WIF 1.1 layout but was not tested against a particular weaving program.
- Stylised cloth: threads are drawn as shaded tubes that dip at interlacings. No yarn twist, crimp, take-up or beating density, and every thread is equally thick.
- Single-lift head: one griffe and one cylinder, as in Jacquard's machine. Later double-lift heads, multiple harnesses and selvedges are not modelled. Real heads had a few hundred to a few thousand hooks; this page allows up to 400 in a repeat.
- Mechanism views are schematic: correct cause and effect, not engineering drawings.
- Loom sound is synthesised (filtered noise), not recorded.