Lifting half the threads
How Does a Loom Turn Thread Into Cloth?
Weaving is not sewing. Long threads are held tight, half of them are lifted, and one thread is passed through the gap.
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Step 1 of 5
Cloth is two sets of threads crossing at right angles.
One set runs the length of the cloth, the other across it. They simply go over and under each other, and the friction at every crossing holds it all together.
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Step 2 of 5
The lengthways threads are strung tight on a frame.
Hundreds of them, side by side, held under tension. This is the slow part — setting up a loom can take longer than weaving the cloth.
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Step 3 of 5
Half of them are lifted, which opens a gap right through.
Every other thread rises together. That triangular gap runs the full width of the loom, and it is the whole reason a loom is faster than doing it by hand.
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Step 4 of 5
A shuttle throws the crossing thread straight through that gap.
In one movement the thread crosses every lengthways thread at once. Then the lift swaps over, trapping it, and the shuttle comes back the other way.
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Step 5 of 5
Changing which threads lift is what makes the pattern.
Lift alternate ones and you get plain cloth. Lift them in threes and you get the diagonal of denim. A loom that reads its lifting order from punched cards was one of the ancestors of the computer.
Cut a woven edge and it frays, because nothing is tied. The selvedge at the side does not fray only because the crossing thread turns round there.
The short version
A loom holds long threads tight, lifts alternate ones to open a gap across the whole width, and shoots a crossing thread through — and the lifting order is the pattern.
Try it yourself
Pull one thread out of the cut edge of an old cloth. It comes away whole, because it was never knotted to anything.