Fabric Washing Techniques

Washing Techniques

These garment washing techniques were originally developed for denim garments, but are now being used for a wide variety of different garment types. The mills and commission houses involved in garment processing continually search for ways to achieve unique new looks.

Most of these garment processors have their own individual techniques, the details of which are not divulged. This technical bulletin describes the basic wash, stonewash, stonewash with chlorine, ice wash, and cellulase wash techniques used for cotton garments.

Any of these procedures can be modified to fit a particular situation, depending upon garment type (i.e., heavyweight denim versus lightweight chambray), available equipment, and process flow. Also, some of these procedures yield garments suitable for overdyeing, which may create a whole new look.

Garment Wash

Indigo jeans were once the only item processed by the garment wash method, but this is no longer the case. A wide variety of different types of woven and knit fabrics dyed by different systems are now used in apparel that is garment washed before retail distribution. Emphasis is on comfort and softness. Also, some fashion trends favour the broken-in look and worn/faded seams that can only be achieved through garment processing.

• Garments can be inverted to minimize unwanted abrasion streaks (especially useful when preset creases are present).
• Load machine with garments.
• Desize with alpha-amylase enzyme and detergent.
• Drain.
• Rinse.
• Fill machine with water and heat to 60°C. The liquor ratio can range from 10:1 to 20:1. A number of synthetic detergents can be used. Also, alkaline products such as soda ash or caustic soda can be added in amounts ranging from 0.5 to 2.0 grams/litre. Some chemical suppliers offer special products that accelerate the washdown process, dependent upon the particular dyestuff used.
• Wash/tumble action for 20-60 minutes, depending upon the desired effect.
• Drain and rinse.
• Apply softener.
• Tumble dry.
• Invert garments, if previously turned.
• Press, if required.

Stone-Wash

In order to accelerate the garment wash effect and to give garments an even more unique appearance and softer hand, abrasive stones were introduced to the wash bath. A variety of natural and synthetic stones are available for stone-washing with perhaps the most widely used being pumice or volcanic rock. As the stones are used, they slowly disintegrate, reducing the severity of the stonewashed effect over a period of time. The stones not only abrade the fabric but also gradually abrade the inside of the rotary drum. A machine used for stone washing should not be used to dye delicate articles or when abrasion would be detrimental to the fabric.

• Load stones into the machine.
• Load garments into the machine (ratio usually 0.5 – 3.0 part weight stones:1 part weight garments).
• Desize with alpha-amylase enzyme and detergent. Liquor ratio approximately 5-8:1.
• Rinse.
• Refill and tumble with stones 30 to 90 minutes, depending upon the desired effect. Liquor ratio 5-8:1 at 50-70°C. Scouring additives can also be used.
• Drain.Separate garments from stones (garments can be transferred to another machine).
• Rinse.
• Apply softener (garments can be transferred to another machine for softening).
• Extract and unload.
• De-stone and tumble dry.
• Press, if required.

Softeners and/or lubricants can be added during steps three and five to reduce creasing potential. Steps 8, 9, and 10 may vary depending upon individual mill arrangement.

Stone-Wash with Chlorine

By incorporating chlorine in the stone washing procedure, a colour reduction of the indigo (or other chlorine sensitive dyestuff) is obtained. It is very important that any residual chlorine is removed before drying to prevent fibre degradation. This is accomplished by using an antichlor step with sodium bisulfite or hydrogen peroxide.

• Load stones into the machine.
• Load garments into the machine (ratio usually 0.5 – 3.0 part weight stones:1 part garments).
• Desize with alpha-amylase enzyme and detergent (liquor ratio approximately 10:1).
• Rinse.
• * Refill and add sodium or calcium hypochlorite.
• Heat to 55°C.
• Tumble 15 minutes.
• Add the second portion of sodium or calcium hypochlorite.
• Tumble 15 minutes, maintaining temperature of 55°C.
• Drain.
• Rinse well.
• Antichlor with sodium bisulfite or hydrogen peroxide.
• Drain.Separate garments from stones (garments can be transferred to another machine).
• Rinse well.
• Apply softener.
• Extract and unload.
• De-stone and tumble dry.
• Press, if required.

* Amount of sodium or calcium hypochlorite required will vary depending upon the desired level of bleach down and the sensitivity of the colour to chlorine.Each addition can range from 0.075% to 0.225% available chlorine.pH should be kept above 9.0, preferably 10.5-11.0.This is accomplished with the addition of soda ash with each addition of hypochlorite.

Ice Wash

Either by accident or experimentation, a method was developed in which stones are used as a vehicle to deposit a chemical on garments to strip the colour. This surface deposit of chemical removes the colour only on the outer surface of the garment and produces a frosted appearance. Indigo and selected sulfur dyes are currently the most popular candidates for this procedure.

• Soak stones in solutions of potassium permanganate for 1-2 hours. Concentrations ranging from 1.5% to 5% are being used commercially. (5% to 10% sodium hypochlorite can be substituted.)
• Stones should be drained of excess liquor. This can be accomplished by placing stones in the net or mesh fabric prior to soaking. -Then the stones can be removed and the excess drained off. Another alternative is to place the stones in a rotary tumble machine along with “waste” fabric and tumbling for several minutes to remove the excess solution. A third alternative is to use any number of the pre-soaked stones or materials available from suppliers. These are available in many different shapes with varying levels of chemical and other additives that produce different effects. Trials should be conducted to determine the best method for achieving the desired effects.
• Place stones and garments in the machine (garments should be scoured and/or desired and dry or slightly damp).
• Tumble for 10-30 minutes or until desired effects is achieved. Results are dependent upon dyestuff, fabric, the concentration of chemicals, stones, additives, and equipment.
• In some cases, the stones can be reused for another load before resoaking, depending upon their porosity. It is advantageous to transfer the garments to another machine for washing, minimizing the number of machines used for the corrosive process of ice washing.
• * If potassium permanganate is used, manganese dioxide will form (a brown/orange colour) and must be removed by treatment with sodium bisulfite, hydroxylamine sulfate, or acidified hydrogen peroxide as the reducing agent. Fill the machine with water and add 1-5 g/l of the reducing agent. Heat to 50°C and run for 20 minutes.
• The process is normally repeated twice to ensure complete removal of the manganese dioxide. When sodium hypochlorite is used, the residual chlorine should be removed with sodium bisulfite or hydrogen peroxide. Adding jeans to a machine already charged with after wash chemicals will increase contrast.
• Rinse well.
• Repeat step 6 if necessary.
• Apply softener.
• Tumble dry.
• Press, if required.

* The selection of sodium hypochlorite versus potassium permanganate depends upon the dyestuff and desired effect. Also, consideration must be given to the safety aspects of handling either chemical.

Cellulase Wash

Cellulase enzymes have gained acceptance in the garment wash industry as a means to achieve a washdown appearance without the use of stones or with reduced quantities of stones. These enzymes are different from the alpha-amylase enzymes used for starch removal in that they are selective only to the cellulose and will not degrade starch. Under certain conditions, their ability to react with cellulose (cotton) will result in surface fibre removal (weight loss). This will give the garments a washed appearance and soft hand.

• Load stones in the machine (normally 0.5 – 2.0 part weight stones: 1 part weight garments) if applicable.
• Load garments.
• Desize with alpha-amylase enzyme and detergent.
• Rinse.
• Add cellulase enzyme (amount, pH, temperature, and cycle time dependent upon the type of fabric and desired effects; manufacturer’s recommendations should be followed).
• Adjust pH as recommended.
• Tumble 30-90 minutes.
• Drain.
• * Rinse well (70°C).
• Drain.
• Rinse well (70°C).
• Drain.Separate garments from stones if used (garments can be transferred to another machine).
• Apply softener.
• Extract and unload.
• De-stone and tumble dry.
• Press, if required. After step 7, a chlorine bleach may be used as described in STONEWASH WITH CHLORINE.

* The increase in temperature serves to deactivate the cellulase. pH adjustment to 9.0-10.0 with soda ash can also be incorporated. Some operations use both the increases in pH and temperature.