What a Tartan Threadcount Is

You will learn how a weaver reads a twill fraction and why that small notation controls the cloth you wear. A fraction such as 2/1 records how many harnesses are raised and how many are lowered when a filling yarn is inserted.

What does a fraction such as 2/1 actually record?

You read the upper number as up and the lower number as down. In the example given on Wikipedia's twill page, 2/1 is read as two up, one down, which means two harnesses are raised and thus two warp threads are crossed, while one harness is lowered when a filling yarn is inserted. The fraction for plain weave is 1/1, so you can see at once that twill asks for a different interlacing rhythm. The minimum number of harnesses needed to produce a twill can be found by totaling the numbers in the fraction, so the described example requires three harnesses. A twill weave requires three or more harnesses, depending on its complexity, and it is the second-most basic weave that can be made on a fairly simple loom. If you are choosing cloth described with wool weights and weave types, that total tells you something practical about loom work before you touch the fabric.

Why does the offset make a diagonal line?

Twill is a type of textile weave with a pattern of parallel, diagonal ribs, and it is one of three fundamental types of weave, along with plain weave and satin. It is made by passing the weft thread over one or more warp threads, then under two or more warp threads and so on, with a step, or offset, between rows to create the characteristic diagonal pattern. A 2/2 twill has two warp threads crossing every two weft threads, while a 3/1 twill is used in denim. The offset at each row forms the diagonal pattern, so you identify the weave by its diagonal lines rather than by colour. In a twill weave, each weft or filling yarn floats across the warp yarns in a progression of interlacings to the right or left, forming a pattern of distinct diagonal lines. This diagonal pattern is also known as a wale.

What is a float and why should you notice it?

A float is the portion of a warp yarn that crosses over two or more weft yarns, and that non-interlacing length affects the fabric's hand and strength. The cited Wikipedia page does not publish a tartan thread count in threads per colour, so you cannot use it to decode colour proportions in a named sett. What you can decode here is interlacing proportion, because the fewer interlacings in twills than in other weaves allow the yarns to move more freely. For that reason, twills are softer, more pliable, and drape better than plain-weave textiles. Due to this structure, twill generally drapes well, which matters when cloth must fall in pleats and hang without stiffness. Twills also recover from creasing better than plain-weave fabrics do, and when there are fewer interlacings, the yarns can be packed closer together to produce high-count fabrics.

How do S and Z tell left from right?

Twill weaves can be classified according to the direction of twill lines on the face of the fabric. S twill, or left-hand twill weave, includes forms such as 2/1 S, while Z twill, or right-hand twill weave, includes forms such as 3/2 Z. If the twill wale goes up to the right on one side, it will go up to the left on the other side. Twill fabrics technically have a front and a back, unlike plain weave, the two sides of which are the same. The front side of the twill is called the technical face and the back the technical back. The cited Wikipedia page explains the diagonal ribs of twill as the visible sign of that direction, and you can use the letter to picture which way the rib climbs. Twill fabrics have no up and down in the weaving process, so direction is about the rib, not about wearing the cloth one way up.

What changes when warp or weft leads the face?

The classification also looks at the face yarn, whether it is warp or weft. Warp face twill weave includes forms such as 4/2 S, weft face twill weave includes forms such as 1/3 Z, and double face twill weave includes forms such as 3/3 Z. The technical face side of a twill weave fabric is the side with the most pronounced wale, and it is usually more durable and attractive; it is most often used as the fashion side of the fabric and is the side visible during weaving. If there are warp floats on the technical face, there will be filling floats on the technical back. Twills can be divided into even-sided, warp-faced, and weft-faced, where even-sided twills have the same number of warp and weft threads visible on both sides, warp-faced twills have more warp threads visible on the face side, and weft-faced twills have more weft threads visible on the face side. The cited Wikipedia page does not publish sett symmetry for tartan, so it gives no mirror rule for colour order.

Can a twill hide soil and soften drape?

Soiling and stains are less noticeable on the uneven surface of twills than on smooth surfaces, such as plain weave, and as a result twills are often used for sturdy work clothing and for durable upholstery, with denim given as an example of a twill. In addition, durability, wrinkle resistance and low maintenance make it ideal for a range of other items, such as jackets, trousers, backpacks and even draperies. Sheer fabrics are rarely made with a twill weave. Since a twill surface already has interesting texture and design, printed twills are much less common than printed plain weaves, and when twills are printed, this is typically done on lightweight fabrics. With higher counts, including high-count twills, the fabric is more durable and is air- and water-resistant. That link between fewer interlacings, closer packing, higher counts and resistance is why an accurate count matters before weaving starts.

Which named twills show even and warp faced cloth?

Even-sided twills listed on the page include foulard or surah, herringbone, houndstooth, serge, sharkskin, and twill flannel. Warp-faced twills listed include cavalry twill, chino, covert, denim, drill, fancy twill, gabardine, and lining twill. A twill with ribs on both sides is called herringbone, and the page also names diamond twill and expanded and multiple forms. According to the stepping, warp-way twills include 3/1 warp-way twill and weft-way twills include 2/3 weft-way twill, while according to the nature of the resulting twill line, simple twill weave includes 1/2 S and 3/1 Z, expanded twill weave includes 4/3 S and 3/2 Z, and multiple twill weave includes 2/3/3/1 S. If you are reading a beginner guide to tartans, keep those categories apart from colour order, because the page does not publish colour order or thread totals for any named tartan.

About the cited Wikipedia page: The cited page is about the type of woven fabric called twill. It describes the 2/2 and 3/1 structures, the offset that forms the diagonal, the fraction notation and harness totals, and the S, Z, face and texture classifications with named examples. Break down the fraction on paper, match the up and down numbers to the face you want, and ask your weaver to confirm the harness total before cloth is ordered.