Stone Washing Process of Denim Fabric

Stone Washing:
Stone washing is a textile manufacturing process used to give a newly manufactured cloth garment a worn-in (or worn-out) appearance. To achieve the desired stone washing effect for the denim garments, the stone should be of proper hardness, shape and size. It is well known that denim garment washing depends greatly on the use of chemicals and stones for achieving the softening and color fading effects. It is a popular wash for denim or canvas fabric. Fabric finishing in the form of stone washing, damaged looks and so forth call for fabrics with even, high strength and robust properties. Furthermore, the fashion trends for denim is moving toward fabrics that are stonewashed or sand washed and have a damaged or even faded look. The denim market covers about 3% of the entire textile market and has been growing steadily over the past years.

A number of people and organizations have claimed to have invented stone washing:

• According to Levi Strauss & Co., Donald Freeland, an employee of the Great Western Garment Company (later acquired by Levi’s), invented ‘stone-washing’ denim in the 1950s.
• Inventor Claude Blankiet has also been credited with having invented the technique in the 1970s.
• The jeans company Edwin claims to have invented the technique in the 1980s.
• In 1982, Lee introduced ‘stone washed’ jeans. This was followed by ‘acid-washed’ denim, which produced an even more faded look.

Stone washed denim gained popularity in the 1960s and remains popular to this day. This type of denim is characterized by a lightly distressed, vintage look. The name comes from the fact that the original processing method involved rubbing pumice stones over the denim to wear down the fabric. Pumice stones are the silica-rich, high-temperature melted product of explosive eruptions during the ascent and expulsion of the earth. These are lightweight, highly porous, rocky substances which will float on water. Major pumice stone–supplying countries are the United States, Turkey, Italy, Iceland, New Zealand, Japan, Indonesia and the Philippines. It is an important component of stonewashed apparels and is used to abrade the surface of the fabric to obtain a surface pattern effect with color contrast and a soft hand.

Because the degree of abrasion may vary in different parts of garments, such as the trouser leg, button slays and seaming parts, a number of neutral patterns can be formed. The degree of the wash effect depends on the stone size, stone ratio, liquor ratio, duration of treatment, amount of garments loaded, garment’s grams per square meter, etc. Stone sizes vary from 1 to 7 cm in diameter. Other washes such as sand, micro and microsand wash are referring to the use of very small size pumice stones.

Flowchart of Denim Stone Washing Process:

Desizing (10–15 min)
↓
Rinsing
↓
Stone washing
↓
Rinsing (with perborate and optical brightener if necessary)
↓
Softening

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.

Denim Stone Washing Process:

1. Load stones into machine.
2. Load denim garments into machine (ratio usually 0.5 – 3.0 part weight stones: 1 part weight garments).
3. Desize with alpha amylase enzyme and detergent. Liquor ratio approximately 5-8:1.
4. Rinse.
5. Refill and tumble with stones 30 to 90 minutes, depending upon desired effect. Liquor ratio 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 softener (garments can be transferred to another machine for softening).
9. Extract and unload.
10. De-stone and tumble dry.
11. 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.

Selection of Stone:
Stones should be selected for their proper hardness, shape and size for the particular end product. Large, hard stones last longer and may be suited only for heavyweight fabrics. Smaller, softer stones can be used for lightweight fabrics and more delicate items (stone weight/fabric weight = 0.5 to 3/1). It depends on the degree of abrasion needed to achieve the desired result. Stones can be reused until they completely disintegrate or wash down the drain.

However that method proves problematic owing to environmental concerns regarding the use of pumice and the fact that the stone often weakens the fabric too much, causing wear and tear. In the process of stone washing, freshly dyed jeans are loaded into large washing machines and tumbled with pumice stone or volcanic rock to achieve a soft hand and desirable look. Variations in composition, hardness, size, shape and porosity make these stone multifunctional. The process is expensive and requires a high capital investment. Pumice stone give the additional effect of a faded or worn look as it abrades the surface of the jeans like sandpaper, removing some dye particles from the surface of the yarn.

Stone Washing of Denim with Pumice Stones has Some Disadvantages:

• Stones could cause wear and tear of the fabric.
• The quality of the abrasion process is difficult to control and the outcome of a load of jeans is never uniform. A slight percentage always gets ruined by too much abrasion.
• The process is nonselective.
• Metal buttons and rivets on the jeans in the washing machines get abraded.
• It creates the problem of the environmental disposition of waste for the grit produced by the stones.
• High labor costs become necessary because the pumice stones and the dust particles they produce need to be physically removed from the pockets of the garments and machines by laborers.
• Denim needs to be washed several times to get rid of the stones completely. The process of stone washing also harms big, expensive laundry machines.

Substitution of Pumice Stone:
To overcome the shortcomings of pumice stones, synthetic stones were developed. These are made of abrasive materials such as silicate, plastic, rubber and Portland cement. Major problems associated with the use of volcanic-grade pumice stone can be overcome by using these products. Advantages of using these synthetic stones are:

1. The durability of such a product is much higher and can be used repeatedly from 50 to 300 cycles, depending on the type of synthetic stone.
2. Reproducibility of washing is manageable.
3. Because there is much less stone discharge in the process, the process is economical and ecological.
4. There is less damage to the machine and garments.

Perlite is a form of naturally occurring silicon rock. It has the distinctive property of expanding to 4 to 20 times its initial volume when heated at a particular temperature. This happens because the raw Perlite rock consists of 26% water. When it is heated above 870°C, crude perlite rock becomes swollen and tiny sealed glass bubbles form. Its original black or grey color changes to greyish white or else white. This heated form of perlite is used for stone wash purposes.

It has the same function of stone washing as stones. Perlite treatment reduces the rate of harm caused to large washing machines by pumice stones and gives denim better suppleness and a softer finish. Many jeans manufacturing companies use Perlite in the place of enzymatic treatment, which reduces the rate at which jeans wear out when used. It gives a uniform worn and old look throughout to the denim, not just the upper part of the garment. There are many grades of Perlite, differing in size. Each is used to giving the right stone wash finish to denim, from the largest to the finest grades; some are very tiny, just like ground earth.

Alternate Methods for Stone Washing:
To minimize the drawbacks explained earlier with pumice, stone-washing of denim is carried out with different methods as explained below.

1. Perlite stone wash: Perlite, a naturally-occurring silicon rock has the distinctive property of expanding 4–20 times its initial volume, when heated at a particular temperature. This happens because the raw perlite rock consists of 2–6% water content in it. The crude perlite rock, when heated at a temperature above 870°C, gets swollen up and tiny glass-sealed bubbles are formed. Its original color is black or grey and it changes to greyish white or white. This heated form of perlite is used for stone washing.

Perlite does the same function of stone-washing as stones. This reduces the rate of harm caused to large washing machines compared to pumice stones and gives the denim better suppleness and softer finish. This also reduces the rate of wearing out of jeans when used. It gives a uniform worn-out and old look to the denim. There are many grades of perlite differing in sizes that are used for giving a stone-wash finish to the denim right from the largest to the finest grades; some are very tiny just like ground earth.

2. Bio-stoning: At first, stone-washing involved using pea gravel, but pumice was discovered to fl oat around with the jeans instead of lying in the bottom of the water and hence, manufacturers have switched. Turkish stone is commonly used for its porosity and cleanliness.

3. Rinse (water) wash: In rinse water wash, the jeans will be washed at about 50°C. There is a high risk of color bleeding, so it is ideal to use old faded jeans for brightening up by washing them together. One should make certain to wash them separately from other garments the first few times. Some jeans brands will not even use Sanforized fabric, so you can shrink them to fit in a hot bath.

4. Dirty wash: After stone-washing the jeans or denim jackets, they will be dyed with special chemicals, thus creating a look in which the jeans will appear to be dirty.

5. Destroyed/damaged/used/whiskers: There are several different techniques to make the jeans or denim jackets look old, worn and/or used. Most of these techniques involve actual sand blasting or abrading by some kind of power tool. Whiskers, which normally appear around the hip to crotch area of the pant, are usually made by using a grinder. Another popular way to make jeans appear damaged is to cut the edges at bottom, (back-) pockets, fly and knee area before the (stone) washing.

References:

1. Denim: Manufacture, Finishing and Applications Edited by Roshan Paul
2. Handbook of Value Addition Processes for Fabrics By B. Purushothama
3. Sustainability in Denim Edited by Subramanian Senthilkannan Muthu
4. Chemical Technology in the Pre-Treatment Processes of Textiles by S. R. Karmakar
5. Chemistry of the Textile Industry By C. Carr

See here Stone and Acid Washing Process of Denim Fabric:
https://www.youtube.com/watch?v=K_Ut9o39QI8

Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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