Aubergine and Tan Bokhara, Hand-Knotted Wool Rug

100% Ghazni wool, hand-spun and naturally rich in lanolin, which gives it softness, a subtle sheen and a natural resistance to everyday dirt and spills. Ghazni wool is prized across the region and is often carried well beyond where it is grown; here it has been used for a Bokhara design.

The aubergine ground is among the most forgiving colours a rug can have — dark enough to hide almost anything, and covered edge to edge in drawing so nothing sits in the open. The tan borders are the exposed part: they run nearly 60cm deep on both long sides, they are the palest large area on the rug, and they sit exactly where people step on and off. At more than ten square metres this is a heavy piece; plan how it will be moved before it goes down.

Run an autocorrelation across the width of this field — slide the pattern over itself and ask how well it matches at each offset — and something unusual turns up. At a shift of 41.7cm the match is strong, 0.77, which is simply the repeat. But at exactly half that distance the correlation is not weak, or near zero as you would expect from an ordinary repeat. It is negative: minus 0.61. The pattern at half a step is the inverse of itself.

That number is the fingerprint of alternation. It happens because the field is not one column repeated across the rug but two, taking turns: a wide column of broad oval güls, then a narrow column of a small barbed device, then güls again. Shift by one full cycle and wide lands on wide. Shift by half and wide lands on narrow, light on dark, and the correlation flips sign. Down the length the same test gives only minus 0.16 at the half-step, so the rows are near enough uniform — the alternation runs one way only. What this buys is a field that fills completely without becoming monotonous. The güls have room to be large and fully drawn, and the narrow columns between them keep the aubergine ground from ever opening into a gap.