Denim Washing:
Over the past few decades, different denim washing techniques have been developed and used on different materials to create a large variety of designs for trendy denim garments and jeans. Special color effects and washed/vintage looks are often achieved in denim garments. The hand feel of the washed goods is relatively superior, which makes them suitable for leisure wear. These effects are difficult to achieve through other processing techniques.
The results obtained from denim washing represent a combined effect of color dissolution, destruction of the dye and mechanical abrasion, which sometimes causes the removal of surface fibers from the materials. Thus surface dyed (ring dyed effect) colors in denim garments are more easily washed down during the washing processes.
Traditionally denim is a 3/1 warp faced twill fabric made from yarn dyed warp and undyed weft yarn. Typical construction of the fabric is 32 × 19; 45 × 54 tex; 310 g/m2. More recently, other weaves have been used with lighter constructions’. Jeans are defined as ‘A 2/1 or 3/1 warp faced twill fabric used chiefly for overalls or casual wear with a typical construction of 35 × 24; 32 × 21 tex cotton’. Although by definition, denim and jeans refer to different things, they now mean the same thing in the market. Conventionally, warp yarn in denim fabric is dyed with indigo with a ring dyed effect. As a result, the washing technique and effect described in this chapter are based on indigo dyed fabric.
Classification of Denim Washing Techniques:
Several types of garment washing for denim fabric are carried out to create varied effects in denim garments to meet the needs of today’s denim fashion trends. However each washing technique has its own advantages and limitations. Denim is either rubbed or worn with stones and other abrasive materials, called mechanical washing, or treated with bleach and other kinds of color-altering substances, known as chemical washing.
Mechanical washes include:
- Rinse wash
- Water jet fading
- Stone wash
- Whiskering
- Microsanding including sandblasting
- Mechanical abrasion
- Laser treatment
Chemical washing includes:
- Acid wash, ice or snow wash
- Hydrogen peroxide wash or Bleach washing
- Enzyme wash
- Ozone fading
- Spray techniques
- Overdyeing and tinting
The effects desired for denim goods change every year owing to fashion. Various washing effects have been popularly obtained by laser, sandblasting and enzymatic washing processes. In addition to these processes, hypochlorite bleaching (acid wash) is often preferred, especially for summer denims.
General Finishing Process of Denim:
There are almost countless variations of processing techniques used by designers and textile chemists to achieve fashionable looks that are distinctive and desirable. Only the basic treatment conditions are addressed in this chapter; the number of variations is very large and the evolution of chemical and mechanical techniques is continuing. There often are some secretive and proprietary methods. Regardless of the specific look and name chosen, the following are the process steps normally used to attain the desired results.
Flow chart of denim finishing
Desizing
↓
Rinsing
↓
Washing (abrasion)
↓
Rinsing
↓
Softening
↓
Drying
↓
Packing
In denim garments, preparation consists primarily of desizing, which enables subsequent chemical and mechanical treatments (washing/abrasion) by removing the previously applied warp size. Untreated denim garments are extremely rigid due to the size applied at the yarn stage for increasing weaving efficiency, by coating the yarn with a protective outer layer which retards yarn breakage. The sizing remains in the yarn after the fabric is woven and, therefore, provides fabric stiffness necessary for more efficient sewing of garments. Sizing is typically made up of starch (or polyvinyl alcohol/starch), binders and waxes and lubricants. Additionally, finishes containing starch and/or polyvinyl alcohol are applied to denim as a topical finish before the fabric is shipped to the sewing plant.
After desizing, denim garments are rinsed to remove all size materials before washing/ abrasion. Different washing/abrasion techniques are introduced in the following sections. Again after the washing/abrasion processes, denim garments are rinsed to remove unwanted materials from fabric surface. Then a softening process enhances the hand feel and softness of the denim garments. Finally the denim garments are dried and packed for delivery.
Desizing:
The most popular method of removing starch from denim garments is to use amylase enzyme. This product can break down the long starch molecular chains (water insoluble) into smaller molecules (water soluble) which can be more easily washed away. The removal of starch from the fabric being desized can also usually release some quantities of indigo into the bath. Therefore, a neutral pH nonionic surfactant is used for suspending loose dye in the water, to prevent redeposition onto the garments as well as to aid penetration of the desizing liquor into the interior of the fibres. It is also important to follow the desizing bath with a hot water rinse. Introduction of cold water onto the denim garments at this point can resolidify the fats and waxes, and tends to redeposit the gelatinous components unevenly on surface.
Rinse wash or Regular washing:
Rinse wash is the simplest type of industrial garment wash. The main aim is to remove starch, dust and dirt from garments. Sometimes reasons for a normal wash include softening and giving the garment a used look. For colour garments, removal of unfixed dyes can be achieved to improve colour fastness. In special cases, intentional shrinkage in garments can be achieved. Precautions need to be taken against unwanted shrinkage issue and back staining.
Regular washing is the simplest and most commonly used washing method for denim garments. It is most basic wash for denim garments. Typically named a dark wash, the only purpose of this wash is to make the garment wearable. The degree of color fading using regular washing is comparatively slight, but it provides uniformity, depending on whether it is deeply dyed classic denim or only moderately dyed with poor penetration. Generally speaking, detergent is used for regular washing for about 15 min at temperatures between 60 °C and 90 °C. Softening is applied after the washing process. Regular washing can improve the softness and comfort properties of denim garments as well as enhance aesthetic property. Depending on the time and amount of chemicals used, regular washing can be classified into (1) light washing (washing time about 5 min); (2) normal washing (washing time about 15 min); and (3) heavy washing (washing time about 30 min). However, there is no significant distinction between light, normal and heavy regular washing as it depends on the actual washing conditions.
Flow chart of general regular washing process is as follows:
Wetting
↓
Desizing
↓
Regular washing
↓
Softening.
A sample recipe for a normal wash is:
If the lot size is 100 kg cotton shirts,
- Material: liquor ratio (M: L ratio)
- Water = 500 L
- Detergent = 1% (based on the weight of the garments)
- Temperature = 40–60°C
- Time = 15–30 min
Back-staining chemical is used if required
Hydrogen peroxide wash or Bleach washing:
Hydrogen peroxide is rarely used as a bleaching agent only when very little loss of colour is required or if the fabric is coated with sulphur, because it takes longer to achieve the desired effect. Hydrogen peroxide has a prime role in the bleach wash technique. In an alkaline medium, hydrogen peroxide breaks up and gives off some perhydroxyl ions, which destroy the colouring matter and result in a fading effect. Hydrogen peroxide is used in a scouring, bleaching bath for white textile material or “ready for dyeing” form of garments made from grey fabrics. We have also published article on bleach wash of denim. You can read below.
Stone washing:
It is one of the most popular denim wash. It gives a newly manufactured denim garments a worn-out appearance. It also helps to increase the softness and flexibility of denim garments otherwise fabric keep stiff and rigid. We have published a comprehensive post on stone wash process of denim garments.
Enzyme washing:
Enzyme wash is a process that gives denim a softer and worn-in look by breaking down the cellulose molecules naturally found in indigo dyes. Denim washing with enzymes is one of the most widely accepted enzyme-based. Enzyme washing of denim with various benefits both economically and environmentally. You can see our complete article on enzyme wash on denim.
Acid, ice and snow wash:
This finish gives indigo jeans sharp contrasts. The process was created in Italy and was patented in 1986. Interestingly, acid wash denim does not use actual acid in the wash process. Instead the process uses pumice stones soaked in bleach to alter the colour in a nonuniform manner. The result is often splotchy yellowish patterns. This finish provides jeans with sharp contrasts in tonal colour. This is also known as ice or snow washing. This is achieved by dry tumbling with pumice stones soaked with bleaching agents to produce a ‘snow’ pattern effect on denim. Stones are used to deposit a chemical on garments to strip off the colour. This chemical deposit removes colour only from the outer surface of the garments and produces a frosted appearance. Indigo and selected sulphur dyes are the most popular candidates for this procedure.
Acid washing:
To change the look of denim or jeans different types of washing process are done. Among various washing process of denim, acid wash is the most popular. This is the oldest of fashion washes in denim after stone wash. You can see our exclusive article on acid washing process in denim jeans.
Microsanding:
A fabric finishing process in which fabrics are sanded (using actual sandpaper) to make the surface soft without hairiness can be performed before or after dyeing. In this fabric treatment process, a series of cylindrical rolls in a horizontal arrangement, either wrapped with an abrasive paper or chemically coated with an abrasive, is used to create a soft suede hand. The denim is pulled over the face of the sand rollers, creating a raised surface finishing. Some colour reduction is experienced.
There are three parts to this technique:
- Sandblasting
- Machine sanding
- Hand sanding or hand brushing
Microsanding is used in various ways: on flat surfaces (tables and ironing boards) or inflatable dummies (standing, flat or seated). Various templates can be used to create a three-dimensional (3D) effect.
Sandblasting:
Sandblasting is a mechanical process of creating fading affect/old looking affect on heavy garments like denim and jeans. There are two types of sandblasting process: manual sandblasting and mechanical sandblasting. Both can be deadly. In manual sandblasting, compressors are used to blow out sand under pressure through a gun in order to bleach and batter the denim. It is very health hazards for workers. It can give factory workers an incurable lung disease. You can see our excellent article on sandblasting process of denim and effects on human health.
Monkey wash or PP spray:
PP Spray is being done on denim garments to achieve local abraded area to appear whiter than back ground indigo color shade. PP Spraying(Monkey Wash) means that to spray potassium permanganate liquid on parts of denim according to design, then there is a chemical reaction on the denim and fading begin. You can see our another article on PP spray techniques on denim jeans.
Brushing/grinding:
Brushing/grinding (manual or mechanical) is used manually or mechanically for the worn-out effect, abraded look or used look. Some mechanical processes have been developed that are based on mechanical abrasion by which the indigo can be removed. Some of these processes are sueding, raising, immersing, peaching and brushing.
Advantages of these processes are as follows:
- Control of the abrasion.
- Different looks on the garment can be achieved.
- All are dry processes.
- Economical, ecological and environmentally friendly.
Brushing is generally being done in a rigid form of garments to get the distressed look. Locations can be front thigh and seat or it can be overall/global application as is standard. In the case of hand brushing, emery paper is used to brush the garments in particular places and designs. Emery paper comes in different numbers, generally starting from 40 to 600 and higher; the higher the number the finer is the emery paper (i.e. a lower is a more coarse paper). In the garment industry, 220, 320 and 400 paper numbers are most popular and widely used.
The purpose of this process is to impart a used worn look to the garments. The most important factor of brushing is to select the right sanding material according to the fabric strength and the intensity needed. Figures 2–4 show the brushing process in factory.
Grinding is done on pocket edges and bottom hems edges by rubbing them against an abrasive surface or stone to achieve a worn effect. Many different makes of machines and pen grinding tools are available in the market which run with pneumatic systems. Figure-5 and Figure-6 show the grinding effect on pocket edges and bottom hems, respectively.
Mechanical abrasion:
To give a worn effect or abraded or used look, some mechanical processes were developed. These are based on mechanical abrasion, which removes the indigo. Some of these processes are sueding, raising, immersing, peaching and brushing.
Advantages of these processes are:
- Abrasion can be controlled.
- A different look to the garment can be achieved.
- All are dry processes.
- The processes are economically, ecologically and environmentally friendly.
Whisker:
Whiskering refers to thin fading lines formed from creases that are usually found on the front pocket area of jeans. It is one of the most important design of a used look denim garment. Now a days it is a common drying process for denim wash. We have also published a article on whiskering process of denim.
Ozone fading:
Ozone destroys indigo color on denim in a manner similar to bleaching. Ozone fading of washed and bleached denim is primarily caused by the oxidative effect of ozone on the indigo dye, the contaminants and the applied additives. Ozone fading gives the advantage of fading with a minimum or hardly any loss. You can see our another article on ozone fading effect on denim.
Laser treatment:
Laser fading or marking is a popular dry process for denim now a day. A carbon dioxide (CO2) laser was used for the colour-fading treatment of denim fabrics. It is sustainable, environment friendly and emerging industrial approaches for the finishing treatments of the denim jeans. You can see laser fading procedure on denim with advantages and disadvantages.
Waterjet fading:
Hydrojet treatment has been developed for patterning and/or enhancing the surface finish, texture, durability and other characteristics of denim garments. Hydrojet treatment generally involves exposing one or both surfaces of the garment through hydrojet nozzles. The degree of colour washout, clarity of patterns and softness of the resulting fabric are related to the type of dye in the fabric and the amount and manner of fluid impact energy applied to the fabric. Particularly good results are obtained with blue indigo dyed denim. As this process does not involve any chemical, it is pollution free. A water recycling system can make this a very economical and environmentally friendly way of denim processing. Colour washout of dye in the striped areas produces a faded effect without blurring, loss of fabric strength or durability, or excessive warp shrinkage.
Dip dyeing:
In dip dyeing, dip dyeing machine is used to achieve special effects on denim garments. Direct dye is commonly used but the colour fastness is comparatively poor and therefore fixation is required to improve fastness. Pigments can also be used for dip dyeing. If a bleaching agent is used, bleaching effect can be achieved on garments.
Pigment washing:
Pigment washing is generally used on pigment dyed or printed garments by applying pigments.
Pigment washing is required for the following reasons:
- To get fading effect/old looking effect on garments and also the seam area.
- For a soft feel to wear the garment after purchasing.
- To achieve the buyer’s washing standard.
- To increase the color and rubbing fastness.
Flow chart of pigment washing:
The basic steps of pigment washing are as follows:
Immersing garment in pigment
↓
Drying
↓
Baking (130–150°C)
↓
Washing (with or without pumice stones/with or without enzyme, 30–90 min)
↓
Washing twice with water at 70°C
↓
Removing stones
↓
Softening
↓
Drying.
Tinting:
After different types of process denim or jeans are dyed with very light color (0.001% or 0.002% yellow or pink). This dyeing process is called Tinting/Overdyeing. Tinting of denim garments is usually done after the stone wash process.
Tie dyeing:
In tie dyeing, a rubber band or similar material is used to tie/bunch the denim garment to make different patterns. Then when carrying out dyeing with a direct dye, the dye cannot enter the tied portion. After dyeing, patterns can be created and fixation is needed. Pigments can also be used in tie dyeing. If bleaching agent is used, bleaching effect can be obtained, which is called ‘tie bleach’.
Plasma Treatment on Denim:
Plasma has been used in the treatment of textiles over the past 2 decades, but a generally available and implemented technology has yet to be developed. Nevertheless, several industrial devices are available as well as numerous examples of custom-designed plasma processing stages for specific industrial production lines. Two directions for development are atmospheric pressure devices and low-pressure plasmas.
There are numerous solutions for atmospheric pressure (or pressures of the order of several 100 Torr) devices, which include glow regime of dielectric barrier discharges and corona discharges. Low-pressure devices, in particular radio-frequency (RF)- powered plasma sources, allow easier control of properties and provide greater stability and uniformity at the cost of more complex handling of the fabric. Corona and RF low-pressure plasma treatments brought about an increase in denim lightness, indicating a removal of indigo dye from the fabric surface. The increased yellowness of the treated denim was more pronounced in case of corona and low-pressure plasma in air in comparison with low-pressure RF plasma in argon. This can be associated with the production of chemically active molecules and radicals in gas mixtures containing oxygen, which consequently leads to an oxidation of dyes.
Low-pressure plasma and corona treatments can be a viable alternative to conventional bio-stoning to obtaining the ‘worn’ look of indigo-dyed denim fabric. In addition to satisfactory color change effects, the main advantages of these treatments are the lack of water consumption and shorter process duration. However, it requires further research to avoid an increase in yellowness and the appearance of a harsh fabric handle.
Corona and RF low-pressure plasma treatments brought about an increase in denim lightness, indicating a removal of indigo dye from the fabric’s surface. The increased yellowness of the treated denim was more pronounced in the case of corona and low-pressure plasma in air compared with low-pressure RF plasma in argon. The formation of pits and striations on the fiber’s surface was more prominent after low-pressure RF plasma than after corona treatment.
References:
- Denim : Manufacture, Finishing and Applications. Edited by Roshan Paul
- Sustainability in Denim. Editors: Subramanian Muthu
- Handbook of Value Addition Processes for Fabrics by B. Purushothama
Editor of Fashion2Apparel. She is a fashion designer and ex-lecturer in Fashion Designing. She wants to spread fashion knowledge throughout the world.
Very informative