Know What You Wear

Friday, December 22, 2017

Stone Wash Process for Denim Garments

Stone wash:
For bringing fading effect on denim stone wash is done. Stone wash also helps to increase the softness and flexibility of otherwise stiff and rigid fabrics such as canvas and denim. This process could result in colour-fading of jeans and there is added usage of water for the washing.

Stone washed jeans
Figure-1: Stone washed jeans
Volcanic rocks or pumice stones (Figure-2) are added during washing as abradants. The colour fading is more apparent but less uniform. The degree of colour fading depends on the washing time (60–120 min), stone ratio (weight of stones relative to weight of the garment) (0.5: 1–3:1), size of stones (diameter: 1–7 cm), liquor ratio (∼10:1) and garment load. The world’s major pumice stone supplying countries include the USA, Turkey, Italy, Germany, Iceland, New Zealand, Japan, Indonesia and Philippines.

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Flow Chart of Stone Wash:
Stone washing process flow chart for any garments is in the following-

Garments loading with stone

De-size

Rinse (Two times)

Stone wash

Rinse (Two times)

Softener

Unload the garments

Extracting

Drying

Stone washing of denim fabric gives ‘used’ or ‘vintage’ look on the garments. This is due to the varying degree of abrasion in the garment. Traditionally, stone washing of denim garments is carried out with pumice stones to achieve a soft hand and desirable look. The pumice stones having an oval and round shape with a rough surface work as an abradant in washing cycle. The variations in shape, composition, hardness and porosity result in different washing effects in the denim fabric. During washing, these stones scrape off dye particles from the surface of the yarn of the denim fabric which shows a faded, worn out and brilliance effect in the denim fabric. From ring dyeing of denim fabric and heavy abrasion during stone washing, the fading is more apparent but less uniform. Stone washing makes the denim garments more supple so that they fit comfortably. To get the desired washed effect, the stone should be of proper hardness, shape and size. For heavy weight denim fabric, large and hard stones are suitable and also last longer. Similarly, smaller and softer stones are suitable for lightweight denim fabrics.

pumice stones
Figure-2: Pumice stones
Procedure of Stone Wash:
The procedure is as follows:

  1. Load stones into the machine.
  2. Load garments into the machine (the ratio is usually 0.5–3.0 part weight stones to 1 part weight garments).
  3. Desize with α-amylase enzyme and detergent. The liquor ratio is approximately 5–8:1.
  4. Rinse.
  5. Refill and tumble with stones for 30–90 min, depending on the desired effect. The Liquor ratio is 5–8:1 at 50–70°C. Scouring additives can also be used.
  6. Drain. Separate garments from stones (garments can be transferred to another machine).
  7. Rinse.
  8. Apply a softener (garments can be transferred to another machine for softening).
  9. Extract and unload.
  10. Destone and tumble dry.
  11. Press, if required.
Softeners and/or lubricants can be added during Steps 3 and 5 to reduce the potential for creasing.

Effect of stone ratio:
Figure-3 shows that with stone ratio below 0.5:1, no significant colour fading effect in the denim garments is noted. When the stone ratio is high, the colour fading effect becomes enhanced. However, too high a stone ratio may cause severe abrasion leading to fabric damage.

Effect of stone ratio on the colour fading effect.
Figure-3: Effect of stone ratio on the colour fading effect.
A: diameter = 2.0–3.5 cm; B: diameter = 3.6–5.0 cm; C: diameter = 5.1–6.5 cm; D: diameter = 5.5–7.0 cm.

Effect of stone size:
Figure-4 shows the effect of stone size on the colour fading effect. It is noted that the smaller the stone size, the better is the colour fading effect. In addition, small stones can provide an even and uniform abrasion effect, but the colour contrast produced is not good when compared with large stones.

Effect of stone size on the colour fading effect
Figure-4: Effect of stone size on the colour fading effect
A: diameter = 2.0–3.5 cm; B: diameter = 3.6–5.0 cm; C: diameter = 5.1–6.5 cm; D: diameter = 5.5–7.0 cm.

Effect of stone washing time:
Figure-5 shows the colour fading effect under the influence of stone washing time. It is shown that after 90 min, there is no further increase in the colour fading in denim garments.

Effect of stone washing time on the colour fading effect
Figure-5: Effect of stone washing time on the colour fading effect
Stone washing of denim fabric with pumice stones has some disadvantages and limitations, such as:
  1. Stones may cause wear and tear of the fabric and may damage the washing machine from abrasion of the stone with fabric or machinery parts.
  2. It may also create the problem of environmental disposition of waste of the grit produced by the stones.
  3. Increase the labour cost required to remove stone dust from finished garments. Denim garments are required to be washed several times for complete removal of the stones.
  4. The stone washing process may cause back staining and redeposition.
  5. The process is non selective.
  6. Metal buttons and rivets in the garments as well as the drum of the washing machine sometimes get abraded which substantially reduces the quality of the garment and the life of the equipment.
You may also like:
  1. Sandblasting on Denim | Health Problems in Sandblasting
  2. Denim and Jeans Manufacturing Process
  3. Different Types of Denim
  4. Denim Fabric Production Process
  5. Denim Washing Process: Objectives, Evolution, Advantages and Limitation
  6. Denim Whiskering Process
  7. Tinting Process in Denim Garments 
References:
  1. Denim : Manufacture, Finishing and Applications. Edited by Roshan Paul
  2. Sustainability in Denim. Editors: Subramanian Muthu