The warp threads (vertical) are stretched between two beams and the weavers, sitting side by side every 90 cm, patiently give birth to the rug knot after knot, row after row.
This technique consists of looping pile yarns around warp threads while a trapped metal rod is used to determine the thickness of the rug. The loops thus formed are left as they are or cut with a blade to open and become piles.
Weft threads (horizontal) are interwoven into the warp threads between each row of knots. This is how the carpet backing is built up and consolidated. The warp and weft threads are usually made of cotton. The vertical loom is also referred to as the High-wrap.
The Tibetan knotis used in Nepal but also in India. This technique consists of looping pile yarns around warp threads while a trapped metal rod is used to determine the thickness of the rug. The loops thus formed are left as they are or cut with a blade to open up and become piles. The Persian knot technique can not be used to make those loops. This method (opening up the knots by cutting them along the metal rod) gives a more or less pronounced lined effect.
The illustration clearly shows the junction of the metal rods of two weavers. It is possible that there is some blurring in this area.
How to measure Tibetan knots:
There are four main counts, namely 60 knots, 80 knots, 100 knots and 150 knots. Knot density varies from one manufacture to another depending on the number of warp and weft threads used. On average 60 knots (60K) corresponds to +/- 60,000 knots per m², 80K to +/- 90,000 knots, 100K to 140,000 knots and 150K to 210,000 knots.
The most sophisticated designs, with curves or diagonals and many colour changes, require a tight knot (minimum 100 knots) to avoid the “staircase” effect.