Denim Finishing

Denim Basic Finishing

Many casual jeans are simply stonewashed and/or treated with enzymes, then softened, dried, inspected, pressed, and finally, shipped.

The process begins when loomstate jeans—that is, jeans that have not yet been through the finishing process—are brought to a rotary washing or belly washing machine and loaded. They may be directly stonewashed or may be desized prior to stoning. Enzymes may also be used either before the stonewashing or with the stonewashing.

Once the process is complete, the jeans are unloaded and transported to an area for de-stoning. There, the stones are removed. Finally, the jeans are then placed in another machine to be washed and softened. At the end of the washing process, the jeans are centrically extracted in the same machine and then unloaded.

Modern rotary machines operate at high extraction speeds so most jeans don’t need additional extraction. But in the case of older machines, a second round of extraction may need to take place. After extraction, the jeans are tumble-dried. They are then sent to be inspected and graded. If they are found to be first quality, they get pressed, bundled, and shipped.

Denim Premium Finishing

Premium jeans go through many of the processes that casual jeans go through with some additions. Typically, those additions involve techniques that age the jeans or give them a special effect.

As in casual jeans, premium jeans begin as loomstate jeans which are brought to a rotary washing machine, loaded, processed with a resin formulation. They are then dried. Once dry, the jeans are taken to be whiskered and pressed. The goal is to give the jeans sharp, distinct whiskers on the lap area and behind the knees.

After whiskering, the jeans are placed on hangers and passed through a continuous curing oven to cure or set the whiskers. The next step in the process is to add additional premium details such as abrading the cuffs with a grinding wheel and performing additional abrasion with a Dremel tool to other areas, such as the pockets and belt loops.

Next comes hand sanding. The jeans are placed on an inflatable mannequin and hand sanding is applied to the whiskers, creases, thighs, hip pockets, and other areas. Another premium step is to apply potassium permanganate discharging chemistry. This is done with a brush with the jeans mounted on an inflatable mannequin.

Once the discharge has developed, the jeans are neutralized and washed in a rotary machine. Enzyme washing may also be performed. As with the casual jeans process, the premium jeans are then centrifugally extracted in the machine and unloaded. If needed, additional extraction may take place. Next, the jeans are tumble-dried, then sent to be inspected. If graded first quality, the jeans are pressed, bundled, and shipped.

Denim Finishing Machinery

Rotary Machines

Rotary drum machines are versatile and accommodate a wide range of fabric types and chemical processes so they are often used for a variety of wet processes. Most rotary machines are side-loading. They are similar to home front-loading washing machines in that they consist of an outer closed cylinder and an inner perforated drum or basket that rotates within the outer cylinder. An access door is located on the side of the outer cylinder. The key advantage of side-loading rotary drum machines is that they require relatively little water to operate.

Garments are loaded into the rotary machine through the outer access door. The door is closed and the external cylinder is filled to between one-quarter and one-third of its volume with water or a processing bath. As the interior drum rotates, the garments become saturated with the bath. Typically, after the drum rotates in one direction, for a specified number of cycles, the direction reverses. This prevents the garments from being tumbled into a dense mass keeps the bath being circulated evenly throughout the contents of the machine.

Side-Loading Rotary Machines

Side-loading rotary machines typically have one of three common types of drums or pockets: an open pocket, a Y pocket, or a lobed pocket. Each pocket has its advantages depending on the type of garment being processed. While open pockets are most often featured on belly washers, they are also used in some side-loading machines. The open pocket design maximizes tumbling and facilitates greater abrasion. Y pockets keep garments from tumbling freely which make them the best choice for items that need minimum agitation and abrasion. Finally, lobed pockets lift the garments allowing increased tumbling with controlled abrasion.

Rotary Drum Machines

Rotary drum machines have several advantages over other types of machines, for one they have microprocessors and computers that allow more precise, sophisticated process control that saves time and materials. Another benefit is their add tanks which can be programmed to add chemicals or dyestuffs automatically without operator intervention. Finally, rotary drum machines remove water or bath solution from garments by centrifugal extraction. This reduces both the number of chemicals or dyestuffs needed for processing and the volume of water needed for rinsing. Garments dry faster and with less energy use.

Front-Loading Machine (Belly Washer)

An older variation on the rotary machine is the front-loading machine or belly washer. These machines have multiple baskets inside the outer cylinder. As with side-loading machines, belly washers have an access door in the outer cylinder but the access door is located in the perimeter rather than the side of the cylinder making it more difficult to reach the inner drum or basket. Because of this restriction, belly washers aren’t as common as they once were but many finishing plants still use them for such processes as desizing and stone washing. This is because they are simple, inexpensive, and easy to use. Belly washers are also large. Some belly washers can hold up to 800 pounds of garments. The disadvantages of these machines though are that they require manual operation and high liquor ratios and lack a high-speed extractor. Liquor ratio is the weight of the water and other chemistries in the bath compared to the weight of the garments.

Wet Processing

Next, let’s take a quick look at how denim garments are wet-processed through rotary washing machines. Before wet processing can begin, denim garments must first be organized into processing lots. For example, one lot may consist of garments that have come directly from cut and sew. Another lot may have already received some type of preparatory process such as sanding or potassium permanganate treatment. Yet another might require additional processing following the wet process.

Processing lots are brought to the washer on a pallet, in a truck, or preloaded into a delivery system such as a sling. The individual processing load is determined by the liquor ratio of the particular processing process to be run. The number of garments in a load can be determined either by weight or by a set count. Modern rotary machines are able to tilt backward for loading and forward to unloading making both processes less complicated.

While belly washers are not able to tilt back for loading, the angle of the door opening makes them fairly easy to load. Typically items can be loaded by hand or, in some cases, by using a sling. For unloading, the machine’s baskets are lifted up and forward. Since belly washers do not have high-speed extractors, the saturated contents are very heavy often making unloading a strenuous job.

Extraction

Once wet processing is complete, the garments go through an extraction process to remove excess water, which minimizes drying time and energy use. Modern rotary machines have excellent extraction capabilities, which are often sufficient for drying. However, if too much water is extracted, unwanted folds and creases can form.

Older rotary machines and belly washers require a separate extraction using a machine designed specifically for that purpose.

After washing and extraction, the machine is tilted forward and a dyehouse truck with an open sling is place in front of it.

The operator then activates the drum so that as it turns, the garments tumble out of the drum and into the truck. The operator hand places that miss the sling. When the slings are full, they are placed in to a centrifugal extractor by either a forklift equipped with a boom or, in some cases, an overhead conveyor system. The sling positions are adjusted for weight balance and the door is closed. The extractor removes water from the garments by spinning the basket at high speed creating centrifugal force. When the process is completed, the door is opened and the slings are removed. They are then transported via forklift to a tumble dryer.

Tumble Drying

Once excess water has been removed, the next step is to tumble dry the garments. The dryer is tilted back for easy loading and the slings containing the garments are placed in side. The machine is then returned to its upright position and the drying process begins. The dryer uses heat, which evaporates the water and tumbling which softens and pre-shrinks the garment.

Most denim washing plants dedicate their dryers by depth of shade. The other colorants for cotton would be direct, reactive, vat, sulfur dyestuffs, and pigment colors.

Whites in particular require their own dryer. Most denim washing houses process white bull denim which would become stained if processed in a dryer where indigo shades have been dried.

Whites notwithstanding, most products which pass through the finishing house do at least maintain a medium indigo shade. These items are dried in a dryer marked indigo or dark. Resins and cross linkers are used to achieve effects currently in vogue such as age marks, including whiskers. They also help improve color retention, decrease shrinkage and result in cleaner surfaces.

Once drying is complete, most of today’s machines unload garments from the back. The garments are then placed on to a truck or conveyor belt for further processing.

Pressing

At various times during the denim finishing process, garments may be pressed to achieve a smooth or ironed appearance. For example, jeans are often pressed to provide a smooth surface for the application of whiskers. Creases or pleats may be pressed into a garment for a vintage look or jeans may be pressed, prior to curing, for a dressier look.

The most common systems for pressing denim jeans are the hot head press, the balloon steamer, and the hand iron.

The hot head press, or the buck press, is the same one used in all phases of garment manufacturing and in laundries. It consists of a lower table or board and an upper head. Jeans are placed perfectly flat on the lower table. The head is lowered, under pressure, onto the garment on the table. A cycle of pressure, steam, and vacuuming then presses the jeans.

The steaming cycle is often called baking. The automatic form press, or balloon steamer, does just what its name suggests: it balloons out to remove wrinkles from a garment. A pair of jeans is placed on the vertical systems so that the waistband surrounds the expandable top. The top grips the jeans and opens the waist. Each pant leg is then gripped at the bottom. The garment is then ballooned, or opened, by applying steam and pumping compressed air inside the garment.

The cycle of steam and expansion is followed by a vacuum step to remove residual moisture and cool the garments. The old reliable pressing system in homes and laundries around the world is the hand iron. In denim garment finishing, the hand irons use is restricted to developing accent effects such as whiskering and for touching up garments for final inspection and packaging. In many places, the hot head has replaced the steamer and the hand iron for these tasks since it gives a smoother, flatter finish.

Denim Wet Finishing Overview

The special character of indigo-dyed yarns offers garment finishers many opportunities to enhance basic denim. One way is through wet processing, which encompasses two techniques: garment washing and garment wet finishing.

Sometimes the terms are used interchangeably but there are differences:

• Washing refers to cleaning impurities from a substrate or removing processing aids.
• Finishing refers to any process other than preparation or coloration that gives a fiber, yarn, fabric, or garment useful or desired characteristics.
• Garment washing can be as simple as removing dirt, oil, grease, or sizing materials from a garment. It may also involve bleaching, enzyme treatments, discharge processes, or overdyeing or tinting.
• Garment wet finishing involves using abrasive agents such as natural stones or chemicals to alter the appearance of the fabric. This might involve removing color, producing contrasting effects, or softening the fabric surface. Wet finishing also includes chemical softening, cross-linking of chemistries or resins, or other technical chemistries.

Popular names given to various wet finishing techniques include stonewash, frosted, snow wash, sand wash, powder wash, galaxy wash, acid wash, electric wash, ice wash, midnight wash, shotgun wash, earth wash, pearl wash, galactic wash, antique wash, and whitewash.

Some of these terms describe a specific garment appearance, some refer to a specific garment processing sequence, and some are used mainly for market identity. While they may have once been proprietary, many of these terms are now considered generic and interchangeable by producer, retailer, and consumer.

Washing & Wet Finishing Techniques

• Desizing/Washing
• Abrasive Color Loss
• Color Discharge
• Chemical Finishing

Desizing/Washing

Desizing denim jeans is necessary to remove the sizing compounds that are applied to the indigo warp yarns prior to weaving. Once the yarns are woven into the fabric, the sizing compounds tend to make the denim harsh and rigid, and they can interfere with subsequent chemical treatments.

The method used to remove warp size depends on the type of sizing used. The most common sizes are starch, PVA, CMC and various binders, waxes anti-stats, and other weaving aids.

A typical desizing process involves loading the machine at a ratio of 8:1 of water weight to fabric weight and using a non-ionic detergent, moderate temperature level, and two to three rinses. If the sizing includes starch, an enzyme is also added to the treatment.

Many consumers prefer darker denim shades that have not been washed down severely. These types of washes are usually referred to as rinse washes because they use a chemical rinse to soften the fabric and fix the color. One example is the dark rinse. Typically a rinse wash consists of desizing, softening and top brightening without an abrasion step, using a cross-linker helps to better retain color. If a rigid hand is desired, the desizing step is omitted which also helps to retain the shade

Stonewashing

Stonewashing is a technique used to accelerate the fading and softening of denim jeans by adding pumice stones to the wash. The stones can be natural or synthetic, in different sizes or shapes, producing varied effects.

The natural pumice stones used in stonewashing are mined and produced in various grades. Pumice is mined around the world in places such as New Mexico, Turkey, Ecuador, and Italy. Due to shipping costs, most of the United States uses domestically mined stones.

Pumice stones range in size from a marble to larger than golf balls. Grades are measured in size by inches and also by their abrading ability. The effect of pumice stones on fabric varies depending on the size, abrasiveness, and volume of stones used per pound of garments. The type of pumice and its mining method affect the size, weight, strength, porosity, and absorbency of these stones.

The rate of attrition, or how long the stones last, depends on the mechanical action of the washing process, the brittleness of the stones, and the desired effect. Pumice stones work by cutting or abrading the surface of the fabric. The grit from the stones sands, scrapes, and cuts the yarns in the fabric and the edges and folds of the garment. Both fiber and dye are removed and the surface becomes softer. The result is an attractive, unevenly dyed appearance that looks faded or aged. Smooth stones yield a more even effect while rough stones provide a more distressed look.

Stonewashing Process

Let’s look at a typical stonewashing process. On average a pair of jeans weighs two pounds, a stonewashing run of 100 pounds of jeans uses 250 pounds of pumice stones and 140 gallons of water for a period of one hour. Then there are more intense stonewashings which can last from four to six hours. Jeans about to be stonewashed may first be subjected to other finishing techniques such as hand sanding or potassium permanganate processing, then they are loaded into a belly washer but they still may not be ready for stonewashing. First, any necessary preparation procedures such as desizing must be performed. Once all preliminary procedures are done, then the stones are finally added to the belly washer. Stonewashing requires exact ratios to achieve a controlled and localized abrasion.

Several factors must be taken into account such as:

• Stone ratio: Typically, the more stones per pound of garment, the greater the abrasion.
• Liquor ratio: The higher the liquor ratio the lighter the abrasion
• Washer diameter: A larger machine diameter means greater machine capacity and higher productivity
• Load size: This is determined in large part by the machine capacity.
• Chemicals: The garment fiber composition and the desired level of abrasion dictate the amount and type of chemicals used.
• Drum speed: Along with the tumbling action of the garments and stones, the speed of the drum directly affects the degree of abrasion.

A typical stonewashing process begins with desizing, followed by stone abrasion, rinsing, top brightening, and softening, You can find out more about a typical stonewash cycle in the technical tips segment of this CD. While some stonewashing is still done in belly washers, rotary machines are becoming the machine of choice. The advantages of rotary machines include larger diameter drums, microprocessor control, and ease of unloading. No matter which type of machine is used thought, it will eventually need to be replaced. Not only is stonewashing hard on the machine’s drum but the stone sludge and small stone particles of its effluent clog waste piping and trenching.

Once the stonewashing cycle is complete, the jeans and stones are removed from the machine. Some stones and stone residue remain on the jeans, because the residue is abrasive it will damage any washer or dryer that the jeans will be loaded into next, so it must be removed either by hand or by machine. Hand-removing stone residue is slow, costly, and labor-intensive. Workers must manually shake the stone residue off the jeans and remove any small stones or particles inside the jeans or in the pockets. It’s virtually impossible to remove all the particles from the pockets which leads to an interesting phenomenon. Consumers often take the remaining residue as a sign of authentic stonewashing. In addition to manual processes, stones and residue can be removed by a destoning machine which is quite efficient and involves very little labor.

After stonewashing the jeans and stones are unloaded into a truck. The truck is moved to the back of the destoning machine and the content is placed inside. The de-stoner consists of a revolving cylinder with spiral veins or baffles inside. As the cylinder turns, the residue is spun out of the garment and through the baffles. The stones drop out of the bottom of the machine into a bin, while the jeans are spiraled through the cylinder and out the back of the machine.

Enzyme Washing

Enzyme washing is a wet processing washing technique that softens the feel of the fabric and brings out highlights. In the jeanswear industry, enzymes are used as an alternative or addition to stonewashing. Enzymes are organic substances, specialized proteins found in all living organisms that serve as natural catalysts for biochemical reactions. They are safe and easy to use and attack and degrade specific substrates under mild conditions. Since they work under mild processing conditions, they cause less damage to denim fabric during processing, or to generate more wear and to give the feel of a full stonewash, enzymes can be combined with pumice stones.

Many different enzymes are used in denim wet processing, each with a specific purpose. The two most often used are alpha-amylase for desizing starch and cellulase for abrasion and biopolishing. The cellulase enzyme biopolishes cotton by hydrolyzing the fiber surface. Unfortunately, this process results in a loss of fiber from the surface of the fabric.

Recently, laccase enzymes have been engineered to decolorize the indigo dyestuffs on the yarns without causing fiber loss. Enzymes offer results similar to those achieved by stonewashing but with several advantages. For example, they are environmentally friendly and require less labor. Jeans washed with enzymes are softer because the enzymes digest the fabric, breaking down the surface fibers. As the surface fiber is removed, so too is the surface color leaving an ultra-clean surface. This gives the jeans a smoother, cleaner appearance even after multiple home launderings.

The major advantages of enzyme treatments over stonewashing are that larger washer loads can be used, no stone handling is required, no de-stoning is required, there is no stone residue, machine wear is reduced which means longer machine life, labor is greatly reduced, and plant noise is greatly diminished. But although enzymes have advantages over stonewashing, they also have some disadvantages. One is that they are moderately expensive, another is that they can cause weight reduction and sometimes strength loss in fibers.

Enzyme applications are any other chemical application technology in that they require certain parameters in order to do their work. The variables that need to be considered include the type of enzyme, the pH of the solution, the temperature of the bath, the time the garments are processed in the bath, enzyme dosage, the liquor ratio, the mechanical action of the machine, any needed auxiliary chemicals and the type of fabric. pH and temperature are perhaps the most important. Many enzymes simply won’t work if pH and temperature limits are exceeded. This is particularly true of cellulase enzyme processing. Mechanical agitation is another key component in enzyme washing since the enzymes themselves only partially remove hydrolyzed cellulosic material mechanical, agitation must do the rest. Agitation also reduces processing time and improves fabric preparation.

As a comparison, let’s take a look at both enzyme-washed and stonewashed denim jeans. With both the stonewashed and enzyme washed, the overall color is similar and the differential washdown around the pockets is also similar. Two types of enzymes are used on denim, neutral enzymes, and acid cellulases; both are effective on cotton denim but result in a slightly different effect as you can see. The type of enzyme used depends on the process being used and the desired effects of that process. For example, a common process is a dark wash using acid-stable enzymes. Its typical processing sequence is desizing, followed by abrasion using acid-stable cellulase with maximum color retention, top brightening, and finally, softening.

Another common enzyme process is the enzyme wash with maximum abrasion. Its processing sequence includes desizing, abrasion using high levels of acid-stable or neutral cellulase enzymes, top brightening, and softening. Yet another process is used for a typical dark wash enzyme procedure that softens fabric while maintaining a dark indigo shade. It includes desizing, followed by abrasion using neutral cellulase with maximum color retention, followed by top brightening and ending with softening. Using the right type of enzyme is critical to maintaining proper pH, which in turn is critical for successful enzyme washing. It’s particularly important to prevent backstaining.

Backstaining

Backstaining occurs when indigo dye removed from the white filling yarns is redeposited on the yarns during processing. Backstaining is less likely to happen during enzyme treatment if a pH greater than 6 is maintained. So neutral enzymes, therefore, allow less backstaining than acid cellulases. But acid cellulases result in greater abrasion so, depending on the desired effect, buffering agents may be used to reduce backstaining in such low pH situations. Backstaining can also be minimized through the use of special dechemicals that prevent the dyes from being redeposited. However, it is important to use the correct specialty chemical, one that won’t adversely affect the cellulase enzyme. Other ways to prevent backstaining include not overloading the machine, using shorter cycles after bleaching, and running extra rinse cycles. A fixing agent can also be used to lock in color. As mentioned earlier, pumice stones can be used with either acid or neutral enzymes. Many washes use porous ceramic or plastic balls called dingers instead of stones. These come in many different sizes and shapes from golf balls to large rubber balls.

The generic procedure for a heavy wash using stones and enzymes is as follows: desizing, then abrasion with a cellulase enzyme in a one-to-one pumice stone to fabric ratio, top brightening, and finally, softening.

Diatomaceous Earth (Di-Earth)

Another way to achieve a novel look for denim is through the use of a naturally occurring material known as diatomaceous earth or di-earth. Di-earth consists of fine fossilized remains of ancient animals. During denim fabric processing, the di-earth abrades the surface of the fabric. In the waste treatment effluent, it readily sinks and is easy to filter. However, di-earth can solidify in drains if it is not completely flushed from the waste system. Di-earth can be used with or without enzymes. The final wash down effect depends on the amount of di-earth used and the length of the abrasion cycle.

Perlite

Another abrasive material used in denim garment finishing is perlite. Perlite is similar to pumice stone and is about 1.5 millimeters in diameter. It produces a softer, more pliable finish than stones or di-earth and also reduces the wear on garment machines. Because perlite is small, it can generate a worn look through the entire fabric and not just on the outer surfaces. Perlite is a processed natural deposit with good abrasive properties. Unlike di-earth, it floats so care must be taken not to use too much. It must also be skimmed during waste treatment and thoroughly flushed from the machines and drains after processing so it does not clog the drains. Some of the names perlite is sold under include Beadwash, Oceanwash, and Pearlwash.

Color Discharge

Discharge washing is a chemical washing technique that removes color from selected areas of dyed fabric. The chemistries used for discharge washing are either strong oxidizers, like potassium permanganate, or reducing agents, like sodium hypochlorite. Ozone processes, which are new to the industry, may offer a clean and simple method for color discharge.

Some popular effects achieved by wet discharge include acid wash, moon wash, fog wash, marble wash, ice frosted, snow wash, electric wash, and galactic wash.

Both chemical and physical systems can be used to discharge color and it can be used as a single, stand-alone process or in various combinations to achieve unique effects. These effects can be placed all over the garment or localized in selected areas. They can be very subtle, slightly less subtle, or remove dyestuff completely from the fabric for the most dramatic effect. Because of its chemical nature, indigo dye is easily discharged. Effects are simple to achieve because the dyestuff is only on the surface of the fiber and yarns making it easy to remove.

Potassium Permanganate

Potassium permanganate is an extremely effective discharge. When it is applied to fabric, the fabric turns a purple-ish brown so you can tell exactly where the chemistry has been applied and when processing is complete, it leaves treated areas completely white. Potassium permanganate is available in liquid, powder, or pellet form. Typically, it’s applied to dry fabric however in some processes, the garment is wet but fully extracted before the chemistry is applied. Treating fabric when it’s dry will result in a whiter discharge. Potassium permanganate can be applied by brushing or spraying both of which create a large or distinct area of discharge. For example, it can be applied to the thighs and seat of the pants to give an aged effect.

Brushing

With brushing, some type of form or mannequin is needed to hold the garment. Jeans, jackets, and other denim items can easily be treated in this manner. Brushing requires some skill to be effective. First, a paintbrush is dipped into a potassium permanganate solution in a paint tray. The excess is brushed onto a fabric blotting-pad to remove any excess liquid. Then the solution is brushed onto the denim surface where the discharge is desired. If the potassium permanganate saturates the jeans or is improperly applied overly white spots or blotchiness can occur. A significant amount of brushing is needed to cover the desired area, so hand brushing is often used to treat very specific areas.

Spraying

For large areas, the preferred treatment method is spraying. As with hand brushing, considerable experience and skill are needed for effective spraying. The garment is usually placed in a booth designed for spray finishing. The garment hangs on a mannequin while the operator sprays it. Water cascades down the back of the booth behind the garment to capture any spray not directed onto the garment. For novel effects, potassium permanganate can be applied to dry fabric that is tied or restricted so that only certain portions of it are exposed to the chemistry. The process is like tie-dyeing.

Garment Washing Machine Treatments

Brushing and spraying are just two application techniques for wet discharge. Another option is to treat the garment in a garment washing machine. This produces an all-over effect in the fabric.

Acid-Washed

A good example of this type of treatment is the acid-washed effect. “Acid-washed” is a misnomer for this well-known process because it uses no acid. Typically, the discharging agent is either sodium hypochlorite or potassium permanganate. A basic acid wash procedure includes preparing the garments, preparing the machine, performing the discharge procedure, running the reduction bath for neutralization, top brightening, softening, and tumble-drying. To prepare jeans for acid washing, they are usually first desized in a separate machine. It is also important to run them through an abrasion cycle such as an enzyme treatment to give some variation to the surface of the fabric. If no abrasion is performed prior to acid washing, the resulting effect will look flat. Finally, the jeans must be uniformly extracted to the lowest possible moisture level. Once they have been extracted, they are moved to a separate acid washing machine.

To prepare the garment machine for acid washing, it first must be drained so that no water is left in the drum. Then the drum holes are covered with a plastic liner. The liner keeps the potassium permanganate-soaked stones used in the process from falling through the holes in the drum. Typically, pumice stones are used weighed at a ratio of 2:1 to dried garment weight, then the stones are soaked for two hours in enough potassium permanganate solution to just cover the top of the stones. The concentration of the potassium permanganate solution can be altered depending on how much discharge is desired. Sodium hypochlorite can also be used instead of potassium permanganate.

Once the stones have been soaked and drained sufficiently, they are placed into the dry machine and tumbled for 5 minutes with white dummy fabric. This removes any excess solution from the stones. The dummy fabric is then removed and replaced with the garments to be processed. The garments are tumbled at high speed, with reversal, for approximately 15 minutes. Both speed and time may need to be adjusted slightly depending on the machine. Once the process is complete, the garments are removed immediately to avoid creating hot spots or areas of complete color discharge in the fabric. The stones are separated from the garments with care taken to ensure that all the stones are removed. The garments are then moved to a separate machine where they are rinsed and neutralized. Finally, they are softened as desired and tumble-dried. Another common washing garment process is called electric wash.

Electric Wash

Electric wash involves the use of potassium permanganate powder and dingers. The process includes preparing the garments, preparing the machines, running the discharge procedure, running the reduction bath or neutralization, top brightening, softening, and tumble-drying. As with acid washing, electric wash garments are first prepared and extracted in another machine. Before they are transferred to the garment washing machine, the machine must first be drained so that no water is left in the drum. The holes of the drum are covered with a plastic liner to keep the potassium permanganate powder from falling through the holes in the drum. The weight of the potassium permanganate should be 45 – 50% of the weight of the garments. The powder is available in strengths from 1% to 4%. Once the powder is weighed, it is placed inside the drum on top of the plastic liner. Next, dingers are weighed at a ratio of 2.5:1 of dry garments and placed on top of the powder. The next step is to place pre-wet garments on top of the dingers. It’s important that the garments touch only the dingers and not the potassium permanganate.

Next, the contents of the machine are tumbled with reversal at 30-35 RPM for 15-20 minutes. As with acid washing, both time and speed may need to be adjusted slightly depending on the machine. Once processed, the garments are removed immediately to avoid creating hot spots in the fabric. The dingers are separated from the garments and the garments are placed in another machine, rinsed, and neutralized with a reduction bath. Then they are softened and tumble-dried.

An alternative to using potassium permanganate powder and dingers is to use potassium permanganate pellets. The process is the same for both, though the pellets are weighed at a 2:1 ratio to the dry weight of the garments. Potassium permanganate pellets can also be made at different strengths.

Bleaching

Bleaching chemistry is like discharge washing in that color is reduced or removed but not necessarily completely. Sodium hypochlorite, which is often used for discharge washing, is also used for bleaching but in a different concentration with a different delivery method and for a different effect. Bleaching alone cannot create localized areas of effect. Localized areas of effect can only occur if the area is first sanded, discharged, or prepared by another method. As with acid washing, bleaching requires an abrasion cycle prior to processing to give some variation to the surface of the fabric, if not the fabric will look flat.

All bleaching uses the same procedures, the only difference is the amount of chemistry used. As you can see, different amounts result in different intensities. A typical bleach down process includes desizing, abrasion using cellulase enzymes, stones (or both), bleaching, neutralization, top brightening, and softening. In bleaching with sodium hypochlorite, the neutralization step is called an anti-chlor.

Hydrogen peroxide is the most used chemistry for the anti-chlor process. Laccase enzyme is used in denim finishing to break down color to achieve an effect like that achieved by bleaching. The most important difference between the two methods is that laccase enzymes don’t require anti-chlor neutralization. This cuts down on the use of water, chemicals, and time. Laccase treatments do require a desizing step with an amylase enzyme and an abrasion cycle prior to the laccase step. The abrasion cycle could use cellulase enzyme, pumice stones, or both. A typical laccase enzyme procedure includes: desizing and abrading the garments, treating them with laccase enzyme, repeating the laccase enzyme step as needed to remove more color, rinsing, softening, and tumble-drying.

Ozone Treatments

Ozone gas is a natural part of the earth’s atmosphere but when ozone is produced by industry or automobile exhaust, it causes air pollution issues. Ozone pollution can cause dyes to oxidize, destroying or changing the color of textiles. This is a particularly troublesome issue in garment shipment and storage. Indigo and sulfur dyes are prone to ozone fading, particularly if back staining has occurred. With regards to indigo-dyed jeans, color discharge is often a desirable effect in denim garments so it stands to reason that controlled ozone treatments could be used to achieve that effect since ozone is such a powerful oxidizer and bleaching agent.

In ozone treatments, the gas is generated as needed and injected into a closed machine. The ozone is used as it is generated. It creates a soft hand and has a washed down appearance like pigment overdyeing. Like other chemical treatments for color reduction, the effects of the ozone process are dependent on time and chemical concentrations and, as with other chemical processes, some form of garment abrasion must be included to give character to the fabric. If proven to be commercially effective, ozone treatment has several benefits over other chemical processes. They include reduced water usage, reduced chemical usage, shorter processing time, effective results on most dyestuffs, and the elimination of fabric degradation. Ozone used in garment washing can be environmentally friendly. In some circumstances, water used during the ozone process can be recycled and reused. Currently, ozone treatments are in the developmental stage.

Top Brightening

After any garment’s wet finishing process, the fabric can be brightened for a cleaner appearance. Top brightening uses sodium perborate in an alkaline bath to create an oxidated scour. The process adds more contrast between the white and light-colored areas and the darker areas of the garment. Top brightening is a simple procedure and is usually applied just before softener application. A typical procedure uses an alkaline detergent and an optical brightener at around 180 degrees Fahrenheit for 15 minutes.

Chemical Finishing

Chemical finishing includes processes like softening, resin finishing, tinting, and overdyeing. Some of these processes require only tumble drying, while others require a curing step.

Softeners

Softeners refer to a wide variety of chemicals, for denim garment applications they must be able to be applied in a rotary machine.

Cationic softeners are a good choice because they produce a fluffy, silky hand on most fabrics. It doesn’t take much to get this effect on cotton because cationic softeners have a positive ionic charge and wet cotton has a negative charge. This gives cotton a high affinity for cationic softeners. Another advantage of cationic softeners is that they easily exhaust and are compatible with most resin finishes. In addition to cationic softeners, non-ionic softeners like polyethylene and many silicones can also be used.

Resin Finishing

Resin is the name commonly applied to chemical compounds that react with cotton or other forms of cellulose. These compounds modify cotton’s performance by improving shape retention, decreasing shrinkage, and improving colorfastness. On denim, the resin is applied for improved color retention, faster development of abraded areas, and helping in the formation of whiskers, pleats, and creases.

The process for resin finishing of denim garments includes applying the resin formulation to the garments, extracting the resin (if needed), tumble drying at a low temperature, pressing (if needed), dry finishing, and oven curing.

Resin finishing is a form of crosslinking in which chemical bonds are created between polymer molecules to form a three-dimensional polymeric network. In addition to the actual resin, resin finishing formulations contain a wetting agent and a catalyst. The catalyst activates the resin and causes the chemical crosslinking to occur. The process is known as curing. For the chemical reaction to be completed, the resin finish must be cured at a high temperature, approximately 300-320 degrees Fahrenheit. This is done in a curing oven—either a semi-continuous batch oven or a continuous oven. A batch oven consists of a reaction chamber in which garments are hung for curing. In some cases, the garments are placed on special hangers and put in the oven one by one. More commonly, an entire rack of garments is rolled into the oven. With a continuous curing oven, garments are placed onto an overhead rail system which moves the garments through the oven. The system’s speed is set for the proper curing time for each product.

When curing takes place after garments have been pressed and dry finished, it’s called a post-cure system. Denim jeans can be post-cured in either one of two methods: immersion or metered addition.

Immersion Method

In the immersion or “dip” process, garments are placed in a garment washer in a bath of the finishing formulation. Once the garments are saturated, excess solution is drained into a storage tank where it is saved for further use. The garments are then centrifugally extracted and tumble-dried at a low temperature in a drier allocated for resonated goods only. If the garments are wrinkled after drying, they are either steamed or hot head-pressed. Then, any desired dry garment finishing effects such as whiskering or pleating are added. Finally, the garments are cured in an oven.

Metered Addition Method

Metered addition is a precisely controlled method for infusing denim garments with a resin formulation as the garments tumble in the garment washing machine. Either dry or wet garments can be finished by metered addition. The process begins when those garments are loaded into an empty rotary machine with a specially designed door with multiple spray heads. A microprocessor turns the spray heads on and off as needed allowing for complete and uniform application of the chemistry to the garment. As the garments begin tumbling, the heads spray a resin bath onto them in precisely the amount needed for a uniform application. There is no waste or bath to pump into a holding tank. Once the garments have tumbled for the correct amount of time for equal abrasion of the chemistry, they are removed from the machine and tumble-dried at a low temperature in a dryer allocated for resinated goods only. When the garments are dry, they may be steam-pressed or if very wrinkled, hot head-pressed. Any desired dry garment finishing effects, such as whiskering or pleating, are added. Finally, the garments are cured in an oven. Metered addition effectively has no chemical waste and uses less water and energy, so it is a more environmentally friendly process. Some of its other benefits include a lower exposure to formaldehyde, the creation of a softer hand than fabric finishing, and decreased shrinkage and better fit.

Tinting & Overdyeing

After processes like discharge and heavy sanding, many denim garments are overdyed. The tint or overdye shows up on those areas of the garment where the discharge or sanding process has removed the indigo color. A common tint is a dirty-looking brown. Some garments have very little indigo dye loss before they are overdyed. In these garments, the white or undyed filling yarns are overdyed. These overdyed shades range from light pastel to dark black. To overdye accented areas, a direct dye is used during one of the final steps in the rotary machine processing. A common overdye bath contains water, a wetting agent, and the dyestuff. The garment is processed for the correct time, temperature, and chemistry. Once the garment is dyed, a softener and color fixing agent are applied. The fixing agent locks in the dye to the fiber, without a fixing agent the dye won’t adhere well to the garment fibers. Once the color is fixed, the garment is finally dried.

Denim Dry Finishing Techniques

In today’s market denim garment designers and finishers must offer innovative products to remain competitive. At the same time, they must keep commercialization time short and maximize their productivity to keep prices within a reasonable range. Current garment dry finishing technology makes this difficult. Dry finishing processes are labor-intensive with low product throughput. The number of steps involved in processing can be high which can greatly increase costs. Fabric degradation during finishing can be significant and the potential for seconds is higher than in most textile processes.

Most dry finishing techniques are aimed at removing the outer core of the indigo-dyed yarn to reveal the white core underneath the surface. As with wet finishing, the character of the yarn itself is the key to effective dry finishing processes. Dry finishing is usually used to create areas of abrasion or color loss that mimic what happens naturally over many wearings and home launderings. Most consumers prefer denim garments that are soft and comfortable. In other words, garments that have been aged to look and feel like something the consumer may have had for years.

Laser

There is significant consumer demand for jeans that appear to be worn or faded at the point of purchase. Many of the traditional techniques for distressing used in denim finishing are not environmentally friendly and may pose hazards to garment workers. Increasingly these methods, such as stone washing, potassium permanganate spraying, sand blasting and hand sanding or dremeling, are replaced with lasers.

Because laser systems are controlled by CAD/CAM technology, almost any distressed effect can be achieved quickly and consistently.

These patterns can be precisely repeated or combined in an infinite number of new and unique worn designs. Laser etching also takes less of a toll on fabric strength retention than many other techniques. Laser etching can create a wide range of effects, for example, holes. When cotton yarn is exposed to high-intensity laser light, it becomes charred. The charred areas quickly form holes when the garment is afterwashed. Cuts and holes of various sizes can be quickly etched and cut by laser.

For more information on laser technology, explore Cotton Incorporated’s technical bulletin on the topic: Laser Applications on Cotton Textiles.

Sanding

For many years, the most popular look for denim jeans has been the distressed, antiqued, or damaged look achieved by localized sanding. Sanding can be done with an industrial sandblaster, with power tools, or by hand with sandpaper. The goal is to create varying levels of abrasion throughout the garment. Typically, more abrasion is applied to those areas that would normally show wear or fray over many wearings.

Hand sanding is a tedious, strenuous, and time-consuming job. Technique must be perfect or unwanted inconsistencies in the worn pattern can occur.

To ensure consistency, workers usually follow a visual standard—a garment whose patterns they replicate. Many manufacturers also mark the boundaries of the areas to be sanded with chalk. The boundaries may be stenciled on or measured. To hand sand a garment, workers use the same types of tools used by carpenters, body shop workers, and other industrial technicians. A common sanding tool is the sanding block or palm sander which is typically homemade to fit a particular employee’s preferences. To prepare for hand sanding, sandpaper is placed on the sanding block. Sandpaper comes in different grits or number of sanding points per square inch which ranges from 100 to 600. The higher the grit number, the finer the sandpaper, and the less aggressive the sanding. The lower the number, the coarser the sandpaper and the greater its sanding capabilities.

Hand Sanding

Hand sanding generates both fiber and grit dust so operators must wear masks. Frequent cleaning of the sanding area is also important. Sanding jeans placed on a mannequin helps keep the jeans expanded and unwrinkled and makes it easier to accurately reproduce the desired look. The pants are loaded onto the deflated mannequin legs and the legs are inflated. Once sanding is complete, the legs are deflated again for easy pant removal. Inflatable mannequins can be made for either vertical or horizontal operations. Some operators find horizontal mannequins easier to work with since they do not have to stretch to reach the upper part of the jeans. Some mannequins can also be raised and lowered or rotated so both sides of the jeans can be sanded from the same location. While some mannequins are for pants, others are for jackets, others can be converted for use with either pants or jackets. Such quick-change mannequins offer great flexibility for sanding, permanganate brushing, or laser techniques.

While most hand sanding is done on mannequins, accent sanding on many premium styles is done on a narrow workbench or flat table. Some areas that are hard to reach by machine sanding methods are also done this way as are garments with an overall wrinkle effect. These garments are free-form sanded by hand. The sanding abrades the high areas of the garment enhancing the wrinkle effect.

Sandblasting

Another traditional technology for abrading denim is sandblasting. In sandblasting, blasting sand or aluminum oxide is pumped under pressure to locally abrade the garment. The stream of sand can cover a range of areas from wide to pinpoint. The entire front of thighs to mid-knee can be sandblasted as can the back of the pockets to mid-thigh.

Fine sandblasting can create effects on the wallet as well as whisker lines across the upper thigh and creases behind the knee. Whiskering often uses templates to ensure that the sandblasting is correctly placed. Sandblasting can also be applied in different degrees. For example, the entire jean can be lightly sanded while specific areas can be heavily sanded. The greatest advantage of sandblasting over hand sanding is speed. This is true whether the area to be abraded is small or large.

Sandblasting also has some disadvantages including inconsistent effects, greater messiness, and the danger of wearing out the fabric if the sandblasting is not properly done. Perhaps the greatest disadvantage to sandblasting is the protective garments and breathing apparatus sandblasting workers must wear. The protective garments can be hot and uncomfortable while the mask makes it hard to see. To precisely abrade specific areas of denim garments, power tools are often used. The high-speed sanding drum is ideal for heavily sanding various edges of a garment such as the cuff, the top of the waistband, and the edge of the fly. Some cuff grinders have only a small slit through which the abrasive wheel touches the cuff, this allows for even more precise abrasion. Some garment areas are too small or hard to reach with a rotary grinder. These areas can be abraded with a Dremel tool-type grinder. Dremel tools can abrade such small areas as waistbands, pocket openings, side seams, belt loops, and flies. Dremel tools are air-operated and can accommodate a wide range of abrasive attachments. Sanding wheels are used most often with varying grits of sandpaper.

Brushing

Brushing is a surface abrasion technique that uses wire- or bristle-covered brushes to give denim an antiqued appearance. The brushes operate at high speed, powered by air or an electric motor. The abrasion produced by the brushes ranges from subtle to severe. Brushing is faster than hand sanding and is usually less destructive.

Narrow brushes are used for whisker effects and hard-to-reach places. Wider brushes are used for larger areas of the garment. Wide surface brushes come in a variety of shapes, each tailored to a specific use. The flat surface brush is an all-purpose brush used to abrade the entire surface of a pair of jeans.

Concave brushes are used to abrade large areas of jeans such as pant legs.

Convex brushes are used on a jacket and the rear part of a pair of pants.

Flat narrow brushes abrade the smallest and hardest to reach areas such as waists, belt loops, whiskers, between the legs of pants, and under the arms on jackets.

Most brushing is done by an operator with a hand-held electric rotary brush. Some brushing is done with programmable, robotic brushes. The hand-held electrical brush is counterweighted from above the operator so that there is little resultant weight for the operator to control.

Whiskering

Whiskers and creases are extremely popular denim garment finishing effects that mimic the abrasion and wear lines normally developed over many wearing cycles. These abrasion and wear lines most often occur horizontally along the lap area, the front of the thighs, the back of the knees, and the bottom of the pant legs. Denim garment finishers have developed effective methods to reproduce these aged effects on new garments. Resin finishing is combined with the use of pressing and abrading tools and techniques to create authentic-looking wrinkles, lines, and creases.

After resin finish has been applied and dried, the technician uses either a hot head press or hand iron to create whiskers and creases. One of the most important steps in the process is to determine where the effect should be placed on the garment so some plants use templates to mark the desired location. Washable lines are marked where whiskers will be placed. Templates vary depending on both the size of the garment and the desired whisker pattern.

Once the jeans are marked, a whiskering technician sets them using either a steam iron and specially designed table or a hot head press. This technician is whiskering a lady’s vest. Notice her skill and manual dexterity in placing the whiskers and the steam iron technique she uses. This operator is using a small hot head press designed for pants to create whiskers. Both pressing methods use steam and pressure to set the creases.

After the whiskers and creases are set, the garments are cured. This sets the whiskers permanently and increases their visibility for the next technician who will use a hand saner to Dremel tool to accentuate the creases.

Special Effects

Some denim aficionados prefer special effects that replicate the look of harsh, even extreme wear and use. These effects can be achieved by scraping, cutting, and making holes—all of which can be done in the denim garment finishing plant.

Broken yarns and holes can be created in the garment by using a scraping or cutting device. The surface of the garment can also be snagged to break yarns which can then be abraded to form holes. Finally, holes can be created by laser etching.

Some of the devices used to create holes and slashes include scalpels, razor blades, and puncturing devices including templates that resemble nail or screw boards. Often, homemade devices are used to create a specific effect and, of course, laser technology is a quick effective method for these same types of effects.

For special abrasion and tied patterns, tacking is used. Tacking protects certain areas of the garment while others are exposed for abrasion such as this whisker on the hip pockets. Tacking can be done either by machine or by hand.

Appliqués are another important technique for enhancing denim jeans. A wide range of objects can be applied to denim to create style and fashion. Combinations of effects are often seen.

Printing is often done using pigments or plastisols, and even glitter.

Other techniques make use of the patching of holes, along with rhinestones and sequins. The opportunities are only limited by the designer’s imagination.