Denim washing and finishing processes

When the indigo blue becomes lighter: From 'used look' to 'stone washed' and 'rinsed washed' – the variety of denim washing and finishing processes is huge. The sewing thread as the most sensitive element of any garment, needs to withstand those different stresses.

Originally developed as robust working trousers for gold prospectors in the USA, classic cotton jeans, made purely out of cotton because of its durability, quickly grew a reputation among farmers, cowboys and loggers. By the beginning of the 1930s, 'blue jeans' were no longer worn strictly for work but had become a permanent part of casual fashion. Then, after the World War II, American soldiers brought the blue jeans to Europe.

Denim is more versatile than ever before

Just as exciting as the history of jeans is the now fashionable variety of shapes and styles. The Levi's 501 is by far the most famous model. In addition to these classic straight fit jeans, there are many other fashionable cuts such as bootcut, boyfriend, skinny, slim fit and high or low waist.

Also the fabric has changed considerably over the years. The once stiff cotton fabric has turned into a very comfortable garment by increasingly adding low proportions of elastane. Also, the cellulose fibre lyocell is becoming more popular for use in jeans and as a substitute for cotton. Today, there are also many more variants than the classic generic "blue jeans": special coloured effects are deliberately applied through a wide variety of finishing processes. But one thing remains: jeans still need to be sewn and the seams must hold or should remain generally intact. On closer inspection of the finishing processes, however, this poses a major challenge.

Washing and finishing processes at a glance

Whether destroyed, fade out or bleached - the conscious 'destruction' of jeans is now a fashion statement. The aim is to make the fabric look old and worn out and/or to remove the depth of colour from the originally dark indigo dye. The variety of the finishing processes used is very extensive. New methods are continuously being developed under a variety of names for the different processes. However, they can be roughly divided into two groups: washing processes (also known as mill-washing) and targeted partial changes to the surface of the fabric by means of chemicals, mechanical actions, or lasers. Combinations of different finishing processes are also frequently used. For example, locally limited techniques are often applied prior to certain washing processes or vice versa.

I. Common washing processes

Standard for classic jeans is the dark blue indigo shade. Through the use of different washes and washing processes, various used looks can be achieved which alter the colour of the dye and the material. This, for example, changes the grip of the fabric or the indigo shade is partially or completely lightened.

rinse means 'flush' or 'wash thoroughly'. This is a simple washing process in which nor chemicals nor other additives are used. The original colour of the jeans remains almost completely unchanged, and the fabric is given a slightly different but natural dry to grainy texture. This washing process also prevents subsequent shrinkage. However, this finishing method has no significant influence on the sewing thread.

As the name 'soft' already suggests, so-called softeners are used in this washing process to make the fabric feel softer but leave the colour almost entirely unaffected. The sewing threads do not suffer any damage in this process, but may also become softer. This washing process also prevents subsequent shrinkage.

Stone washing is a classic washing process which gives jeans an individual used look. Through multiple baths with pumice stones, the denim fabric and thus the colour is rubbed off mechanically. Depending on the type, size and surface of the pumice stones, as well as the washing time, a more or less strong used look can be achieved. The mechanics of the stones give an authentic used look to both, the fabric of the jeans as well as the seams. Thus, a high abrasion resistance of the sewing thread is necessary. Choosing the right thread count is also of great importance. The thinner the thread, the easier it can be destroyed by pumice stones.

A similar effect to stone washing can be achieved by the use of enzymes. There are different types of enzymes used, but all of them cause a certain chemical reaction. For example, bleaching the indigo dye or changing the grip of the fabric by breaking and removing protruding cotton fibres. Using this method, it is also important that the sewing threads are not attacked by the enzymes and thus lose its strength. Polyester threads, for example, are particularly robust and enzymes usually cannot harm them.

Bleaching makes jeans brighter and enhances their colour. The longer the bath in the bleaching agent, the lighter the indigo blue of the jeans can become. A common method is bleaching with chemicals such as hypochlorite and/or permanganate. Besides, more and more environmentally friendly bleaching methods, such as ozone, are becoming established. However, colour effects are usually not desired with regard to the sewing threads. Thus, it is important that the sewing yarns are not attacked – no matter which bleaching agent or method is used. Consequently, the sewing threads should have a high fastness against the corresponding bleaching agent.

II. Partial finishing processes

In addition to the numerous washing processes, there are also methods for finishing jeans which do not affect the entire piece of clothing, unlike washing. For example, there are partial finishing methods which achieve authentic and natural used looks, so-called 'worn-out looks', movement and seat folds or special patterns.

A partial used look on Denim can be created by a specific spray treatment with bleaching agents. However, as in the washing process with bleaching agents, it should be taken care that the dyeing of the sewing thread is resistant to the respective bleaching agent to avoid undesirable effects.

By means of different sanding and brushing techniques, very natural but also detailed used looks can be produced. Dye and fibres are rubbed off mechanically from the denim's surface. This requires both, experience and precise manual work. The most important technique is manual sanding using special sanding paper. The finished jeans are placed on mannequins and then processed with sanding paper, which usually achieves rather light effects. Manual brushing, on the other hand, produces coarser and bigger effects. There are also fully automated brushing robots that can be used to produce very precise used effects and which are usually more cost-effectively than by hand. Mostly, these effects are created within the surface so that the seams are not affected. However, these techniques can also be used to deliberately destroy the seams in order to achieve special used effects.

An alternative technique to sanding, brushing and the use of chemicals is lasering. Whether lightening the surface or partial brightening or engraving logos and patterns into the fabric: the laser beam can deliberately fade the dye, slightly scratch or even destroy the top fabric layer, creating holes or cracks. It has to be considered however, that synthetic fibres such as PES, polyamide or lycra can melt and leave hard residues. Lasering therefore is limited to cotton outer fabrics, but also the material composition of the sewing thread must be taken into account. Although the advantage of laser technology is the precise processing of fabric surfaces, it is usually also more expensive than other methods.

Robust denim threads for various finishes

Since the sewing thread is the most vulnerable element of a garment, it must withstand these versatile stresses. Depending on the finishing method used, it is therefore important to choose the right thread in order to withstand any type of strain. Our denim sewing threads are regularly tested in our sewing laboratories under extreme conditions and are ideally suited for a wide range of washing and finishing processes due to their high durability and colour fastness.

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