In Persian Carpets, tying a short length of yarn around two adjacent warp strands so that the ends of the yarn protrude upwards and form the surface (pile) of the carpet creates the pile.This process is referred to as knotting. The proximity and density of the knots contribute to the fineness and the long wear of the carpet.With more knots, the pattern and design of the carpet are highlighted . In the Persian carpet weaving two main types of knots are used, the Double knot or ( Turkish ) and the Single knot ( Persian ).
Single or Persian knot
The knot is formed by looping the pile yarn through warp strands and then drawing back through one.
It's also referred to as "asymmetrical" knot, because the pile yarn may be drawn to either the right or left of the warp strands.
The Persian knot is mostly used in Eastern, South Eastern and the Central Provinces of Iran like Mashhad, Yazd, Kerman, Arak, Ghom, Esfahan, Kashan and Tehran.
Double or Turkish knot
It's a fraudulent knot used by some dishonest weavers. The knot is produced by tying the pile yarn around four or six warps strands rather than the customary two. It improves the speed at which the carpet is woven but result in poor structure and is less compact and durable.
Finesses of knotting
This refers to the number of knots in length is referred to as (Raj) viz a 50 (Raj) carpet has in length 50 knots in every seven centimeters.
In some weaving centres of Iran, one of which is Azarbaijan, the counting is done on an area of 49 square centimeters (7*7cm) but in reality the best method is to multiply the counted knots on the surface of the carpet in one square centimeter.
If the carpet is woven accurately and with precision the number of knots in length and width should usually be the same but it often happens that the number of knots along warp is more than along the weft.
The number of knots is one of the main indicators of the fineness of a carpet. The higher number of knots per square metre, the finer the weave is considered to be. Carpets are often classified by Fineness under following scale :
| 1 | Coarse carpets known as "khersak" | 36 to 50 thousand knots per square meter |
| 2 | Medium coarse carpets | 50 to 100 thousand knots per square metre |
| 3 | Ordinary/medium | 100 to 200 thousand knots per square metre |
| 4 | Medium/fine | 200 to 325 thousand knots per square metre |
| 5 | Fine | 325 to 500 thousand knots per square metre |
| 6 | Extra-Ordinary/Fine | 500 thousand to 1 million knots per square metre |
| 7 | Exceptionally rare | Woven with silk filaments and have more than one million knots per square metre |