Yarn producers look for cotton fibre that has a uniform fineness for strength and dyeability – a fibrr that’s not too long or too short, but that has uniform length that will give the yarn strength. The yarns are spun using either open-end spinning or ring- spinning equipment. All denim yarn before the 70 s were ring-spun. Then open-end spinning came along. Open- end spinning, often referred to by the initials O.E. , is an efficient yarn spinning technology that skip several processes that ring yarns must go through, making the yarns faster and less expensive to produce. Cotton fibres are “mock twisted” by blowing the fibres together, creating bulkier yarns and thus bulkier, coarser looking and coarser- feeling denim. Without the uniform twisting of the fibre, open-end yarns lack the inherent strength of ring-spun yarns.
The current trend is toward a softer feel or "hand" in denim and a more authentic, vintage look. Ring–spun denim and a more authentic, vintage look. RING-SPUN denim is the original type of denim fabric woven using ring-spun yarns. Yarn produced by this method creates unique surface characteristics in the fabric, including a desirable unevenness giving jeans a nice authentic vintage look. Ring yarns add strength, softness, and character to denim fabric. The largest producer of ring-spun denim today is Cone Mills.
One way to reduce the cost of a true ring-spun product is to weave ring and open-end yarns together the technique is often referred to as RING /OE- the warp yarn is ring-spun, the WEFT or FILLING yarn is open- end spun. You still get the stronger, softer hand of a ring-spun product, but you begin to compromise the unique yarn characteristics in ring-ring denim.
FAUX (or fake) RING-SPUN is a variation of open-end that makes the final fabric appear to be ring-spun. Although slubs appear in the fabric, you still do not have the inherent strength, softness and flatness of the real McCoy.
The main thing that makes denim unique from other bottom weight fabrics is that the WARP (lengthwise) yarns are dyed indigo or other colours in what is known as a Rope form to weaving. All good authentic ring indigo denim is ROPE DYED. Three hundred to 400 ends ( or threads) are gathered to form a rope, then 12 to 36 ropes are dipped in a series of dye boxes along an indigo dye range. The ropes are then washed, dried and beamed (or separated)- and finally woven.
RING DYEING is another uniqe characteristic of denim and indigo dye, and refers to the fact only the outer ring of fibers in the yarn are dyed, leaving an undyed core in the yarn. This promotes abrasion, fading and adds visual interest.
To enhance the ring dyed effect, warp yarns can be MERCERIEZED, or pre-treated with caustic soda, to improve the luster of the cotton fiber and increase its strength and affinity for dyes. This technique was particularly popular during the acid wash days when a high contrast look was desired. Because the cotton fibers are pretreated. Color adheres to the outer fibers much more quickly, leaving the core of the yarn cleaner. When stonewashed, the color literally chips off, promoting faster abrasion.
However, the effect creates a very high and low contrast between the indigo and the white core of the yarn, creating a “synthetic” salt- and-pepper appearance to the garment.
Warp yarns can also be pretreated with sulphur dye prior being dyed in indigo, which is called a SULPHUR BOTTOM. This offers two benefits:1) a quicker wash-down effect because the sulphur protects the core of the yarn from the indigo dye and 2) a cast or hue change. A SULPHUR TOP refers to yarns that have been dyed with sulphur after they have been dyed with sulphur after they have been indigo-dyed . this process was more common prior to the invention of stonewashing as a means of adding depth to the overall color. Today it is more often used in novelty dyeing to create different looks.
Sulphur dye combined with indigo can change the CAST, or HUE, of the fabric. For example, if a black sulphur dye is used, the denim will have a gray cast that, after wet processing, creates a jean with an authentic antiqued, secondhand look.
As Edward Malick, director of technology, Buffalo Color Corp. points out, “indigo is such a poor dyestuff. If it were discovered today, it would not go to market because of that, but it’s those very poor performance characteristics that make denim fabric so unique and attractive.” These qualities are why indigo is the world’s most popular dyestuff; in the U.S, more than 27 million pounds of it are used annually.
Each time the threads are DIPPED in indigo, the shade darkens achieving different degrees of depth. Two dips of indigo equals a four percent indigo concentration on weight of yarn. Four dips is an eight percent concentration, eight dips is equal to a 16 percent concentration and a 16 dip is a 32 percent concentration of indigo on weight of yarn. In other words, each dip corresponds to two percent of the shade. The 32 percent indigo is the darkest. Retailers will have more of that this year as dark and rigid indigo, again a reflection of the popularity of vintage look. Returns to the forefront of fashion.
Black is perhaps the most popular shade after indigo. The search for the ultimate pair of black jeans that will maintain their depth of color after commercial washing and multiple home launderings is an ongoing process. Black denim yarns are dyed differently from indigo-colored yarns in that yarns to be dyed bleck are dipped once rather than several times. When black is applied to yarn, it is generally done using sulphur dyes. SULPHUR DYES have a rapid strike rate, compared to indigo dyes. A 20 second dip can produce a very dark black shade, depending on the amount of dye in the bath.
FIXATIVES are used to lock on the dye either in fabric manufacturing or during garment wet-pro-cessing. Yarn preparation, like mercerization (as discussed above), is another alternative to producing color fastness.
OVERDYEING, a process that can take many form, is another way of achieving a deeper saturated color or unusual shade effects. Overdyeing results in different looks for colored denim jeans. In yarn form, indigo-dyed yarns can be overdyed, or TOPPED another color, to enhance or change the cast or hue. In fabric form, yarn-dyed denim is overdyed a second color to create a saturated, almost piece-dyed effect. Overdyeing in garment form is referred to as GARMENT DYING. Here denim jeans are dyed in the laundry.
Denim fabric can be woven in a multitude of WEIGHTS, from four to 14-plus ounces. Lately, silhouette changes, styling changes and the growing casual trend have created an increasing demand for light ( 6-10 oz.) and mid-weight (11-13 oz.) denims. They add newness to the traditional five pocket jean.
Weaving is where the warp and filling yarns are interlaced. The type of weave in the fabric makes quite a diggerence in the end product. In RIGHT HAND with denims the twill line rises to the right, which creates that recognizable denim twill weave. LEFT-HAND twill, which is growing in demand, has the diagonal twill line rising to the left. The combination of yarns spun in one direction and the fabric woven in the opposite direction (left), causes the yarns to open up when the fabric is abraded in stonewashing. This tends to create a softer, loftier denim.
BROKEN TWILL, first used by Wrangler in the early 1960s, is the denim weave preferred by cowboys. Wrangler’s Pro Rodeo brand, sold to western stores, is one example of broken twill. The broken twill is a balanced construction in which the diagonal twill line changes direction this breaking of the continuous twill line reduces the torque in the fabric and prior to skewing technology, reduced the leg twisting that was a common problem in early jeans constructions.
Today mills have solved the problem of leg twisting in garments by SKEWING the fabric during the finishing process. This is achieved by contorting the fabric to its natural after-wash configuration. Cone Mills was the first manufacturer to Sanforize and skew fabrics. Additional terms you may want to keep on hand when helping cusomers are mill-washed, ring-dyed and selvage. MILL-WASHED refers to the fabric being washed in the mill prior to garment manufacturing to remove loose color and soften the fabric. With the return of the rigid denim look in fashion, wach for this finishing technique to grow in popularity.
SELVEDGE is the narrow, white woven edge of fabric parallel to the warp. It prevents ravelling and is usually stitched with a coloured thread. Originally, denim fabric was woven on narrow looms and the selvage was utilized in the final garment, usually visible inside the jeans along the inner leg. The insertion of coloured thread in the selvage is used as an identification system by the mills as a way to distinguish one customer’s fabric from another’s in inventory and during manufacturing. For example, red thread for Levi’s, green for Lee and yellow for Wrangler. With the growing appeal of vintage jeans, some companies, such as Levi’s, have reintroduced selvage jeans as a fashion trend.Denim is the common thread with universal appeal. Inspired by the past and influenced by the ideas of contemporary culture, the jeanswear industry must constantly reinvent itself. Continued advances in technology will enable all of us to develop products that meet the changing demands for styling and performance. But, it is the information exchanged and the knowledge shared between ourselves, our customers and our consumers that will keep denim and jeans in the forefront of fashion.