thumb|right|alt=Photo of three samples of tartan cloth, blue, grey, and red, the grey in a subtle palette, the others bright|Three tartans; the left and right are made with the "modern" dye palette; the middle is made with "muted" colours.

thumb|right|alt=Montage of 9 tartan designs, from simple to complex, and in a wide range of colours|Tartans come in a wide variety of colours and patterns.

thumb|right|alt=A purple-red-and-green tartan skirt and jumper (sweater) on a mannequin|1970s [[Missoni tartan knit jumper (sweater) and skirt set]]

Tartan ( ), also known, especially in American English, as plaid (), is a patterned cloth consisting of crossing horizontal and vertical bands in multiple colours, forming repeating symmetrical patterns known as setts. Tartan patterns vary in complexity, from simple two-colour designs to intricate motifs with over twenty hues. Originating in woven wool, tartan is most strongly associated with Scotland, where it has been used for centuries in traditional clothing such as the kilt. Specific tartans are linked to Scottish clans, families, or regions, with patterns and colours derived historically from local natural dyes (now supplanted by artificial ones). Tartans also serve institutional roles, including military uniforms and organisational branding.

Tartan became a symbol of Scottish identity, especially from the 17th century onward, despite a ban under the Dress Act 1746 lasting about two generations following the Jacobite rising of 1745. The 19th-century Highland Revival popularized tartan globally by associating it with Highland dress and the Scottish diaspora. Today, tartan is used worldwide in clothing, accessories, and design, transcending its traditional roots. Modern tartans are registered for organisations, individuals, and commemorative purposes, with thousands of designs in the Scottish Register of Tartans.

While often linked to Scottish heritage, tartans exist in other cultures, such as Africa, East and South Asia, and Eastern Europe. The earliest surviving samples of tartan-style cloth are around 3,000 years old and were discovered in Xinjiang, China.

Etymology and terminology

The English and Scots word tartan is possibly derived from French meaning 'linsey-woolsey cloth'. or from French or (occurring in 1454 spelled ) meaning 'Tartar cloth'. Patterned cloth from the Gaelic-speaking Scottish Highlands was called , meaning 'many colours'. Over time, the meanings of tartan and were combined to describe a certain type of pattern on a certain type of cloth. Sett can refer to either the minimal visual presentation of the complete tartan pattern or to a textual representation of it (in a thread count).

In North America, the term plaid is commonly used to refer to tartan. Plaid, derived from the Scottish Gaelic meaning 'blanket', was first used of any rectangular garment, sometimes made up of tartan, which could be worn several ways: the belted plaid () or "great kilt" which preceded the modern kilt; the arisaid (), a large shawl that could be wrapped into a dress; and several types of shoulder cape, such as the full plaid and fly plaid. In time, plaid was used to describe blankets themselves. or pladding was sometimes used to refer to tartan cloth.

Weaving and design

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Weaving construction

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thumb|alt=Simple diagram of black weft threads being woven under two orange warp threads then over two of the warp threads|Visualisation of 2/2 twill weave: the black weft threads go two over then two under the orange warp threads, staggered by one thread each pass (resulting in a diagonal pattern). In the actual cloth, the white gaps would be closed.

The Scottish Register of Tartans provides the following summary definition of tartan:

thumb|right|alt=Close-up view of scarlet red, black, yellow, azure bleu, and crimson red tartan cloth|Close-up view of traditional tartan cloth, showing pattern of diagonal "ribs" of colour; this is a five-colour tartan, in scarlet red, black, yellow, azure blue, and crimson red.

In more detail, traditional tartan cloth is a tight, staggered 2/2 twill weave of worsted wool: the horizontal weft (also woof or fill) is woven in a simple arrangement of two-over-two-under the fixed, vertical warp, advancing one thread at each pass. Where a thread in the weft crosses threads of the same colour in the warp, this produces a solid colour on the tartan, while a weft thread crossing warp threads of a different colour produces an equal admixture of the two colours alternating, producing the appearance of a third colour&nbsp;– a halftone blend or mixture&nbsp;– when viewed from further back. This means that the more stripes and colours used, the more blurred and subdued the tartan's pattern becomes.

James D. Scarlett (2008) offered a definition of a usual tartan pattern (some types of tartan deviate from the particulars of this definition): starts at an edge and either reverses or (rarely) repeats on what are called pivot points or pivots. In diagram A, the sett begins at the first pivot, reverses at the second pivot, continues, then reverses again at the next pivot, and will carry on in this manner horizontally. In diagram B, the sett proceeds in the same way as in the warp but vertically. The diagrams illustrate the construction of a typical symmetric (also symmetrical, or mirroring) tartan. However, on a rare asymmetric (asymmetrical, An old term for the latter type is cheek or cheeck pattern. Also, some tartans (very few among traditional Scottish tartans) do not have exactly the same sett for the warp and weft. This means the warp and weft will have differing thread counts . Asymmetric and differing-warp-and-weft patterns are more common in madras cloth and some other weaving traditions than in Scottish tartan.

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File:Tartan diagram (warp and weft) A.svg|Diagram A, the warp

File:Tartan diagram (warp and weft) B.svg|Diagram B, the weft

File:Tartan diagram (warp and weft) C.svg|Diagram C, the tartan. The combining of the warp and weft.

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A tartan is recorded by counting the threads of each colour that appear in the sett.