Although tartans have been a part of Scottish dress for centuries, the association of specific tartans with particular clans only dates back to the 18th Century. The ban was finally repealed in 1782 and it is after this that a revival of interest in tartans began. Their popularity was greatly helped by Sir Walter Scott's novels, and Queen Victoria's love of Scotland. Generally each clan has a tartan determined by the chief of that clan. If you are a member of the clan, then you may wear that tartan, although fashion often dictates otherwise.
Some clans have only one tartan, others have many.
Most tartans are symmetrical, having the same pattern in both the warp and weft. The hardest part is determining the pattern of sett. In the example, the Angus tartan, we have a three color tartan blue, black and red. The red section is broken up into smaller lines, so its sett is pretty easy to determine. Starting from the top, there is a pattern of one narrow red stripe, followed by a blue stripe of equal width.