The structural difference
A kani piece is woven. The pattern is built into the cloth as it is made, using small wooden bobbins called kanis, each carrying one colour, worked back and forth only across the width of their own colour block. There is no shuttle thrown across the full width. Pull a kani shawl apart and the pattern is the fabric.
A sozni piece is embroidered. The ground cloth — usually plain pashmina — is woven first, and the pattern is worked onto it afterwards with a needle and floss silk. Pull a sozni shawl apart and you have a plain shawl and some thread.
Neither is better. They are different objects with different failure modes: kani cannot fade or lift because the pattern is structural, while sozni can achieve a fineness of line that weaving cannot.
Why kani takes longer
Before weaving begins, a kani design is written out in talim — a coded notation recording, row by row, how many warp threads take which colour. Writing the talim for a complex design is itself weeks of work, done before a single thread is laid.
Then the loom is occupied. A single weft row on an intricate design can require thirty or more separate bobbin movements, and a full-width shawl runs to well over a thousand rows. The loom cannot be used for anything else in the meantime, and the weaver cannot go faster without the pattern drifting.
Why sozni pricing is driven by coverage
Sozni is priced by how much of the ground is covered and how fine the stitch is. A border-only shawl is months of work; a full-field jaal, where the embroidery covers the entire surface, can occupy one person for the better part of a year.
The most demanding sozni is do-rukha — worked so both faces are finished with no visible reverse, sometimes in different colourways on each side. There is no shortcut: the design is worked twice, in register.
A note on kalamkari
Kani and kalamkari are sometimes confused because both appear in discussions of Indian textile art, but they are unrelated. Kalamkari is a hand-painted and block-printed cotton tradition from Andhra Pradesh and Telangana, using natural dyes and a pen-like kalam. It is painted onto cloth; kani is woven into it. Different regions, different techniques, different price structures entirely.