Caring for leather16 May 2004
Do you remember dubbin? It was a sticky oily paste that schoolboys were encouraged to apply to their football boots 40-50 years ago to keep them clean and supple, if you could call the leather that football boots were made from in those days 'supple'. Nowadays, the name 'dubbin' is rarely mentioned; indeed most people have probably never heard of it. In fact, it is defined as being 'an application of tallow and oil for dressing leather'. Since those days, there have been huge changes in the performance of leather used for sporting applications. In the past, sporting leather was normally heavy, tan coloured and its surface was relatively unattractive, although very practical, and offered a degree of protection, especially against the players in opposing teams who took a delight in kicking ankles! How different leather for sporting footwear applications is today! And how different are the methods of caring for it! Leather for sports and leisure footwear Surface appearance, performance and lightness of weight are now the most important features of sports footwear. Leather for many sports and leisure applications needs to be lightweight, soft and attractive. At the same time, it must stand up to the rigours of the sports field or such leisure activities as running, climbing and trekking. In doing so, it must provide the necessary support and protection for feet, toes and ankles to avoid damage to muscles, surface tissues and bones. It must also stand up to exposure to cold and wet conditions and be resistant to heavy abrasion. White is the predominant colour for the casual sport shoe market, more especially for leisure applications, although recently there has been a move in this area towards darker colours or combinations with navy blue, red, green, orange and black. Trims and decorations tend to be in contrasting colours and may include corporate logos that may be permanently embossed into the leather surface. The modern technique of injection moulding sole units enables layering of different colours of material such as polyurethane and thermoplastic rubber. This facility allows designers to blend the style of the sole with the upper, or alternatively the sole may be painted to complement the shade of the upper. In contrast, field sports such as football (English and American), rugby and hockey use mainly dark colours, usually black, with contrasting trim and logos in lighter colours. There are, of course, a number of sports that have special needs. Riding boots and climbing boots both have particular requirements dictated by the needs of the sport and by its traditions. Leather for shoes In addition to conventional footwear that includes the world of fashion design and colours, there is always a need for shoes for heavy-duty use. Two examples are footwear produced for industrial uses including safety footwear, and military boots, both of which are often strengthened with metal toe caps and heel supports. Fashion colours are not usually a part of this scene; it is simply black, beige or brown! And the footwear is usually made from full grain, corrected grain or even nubuck leathers! Footwear for children is another major application that is also more demanding, simply because the leather upper surface needs to withstand the far greater scuffing that results from play and rough treatment. Caring in the tannery When footwear leather uppers are regularly treated with the correct choice of aftercare products, the life expectancy of the footwear should be greatly extended. However, the longevity of the leather is actually determined in the tannery! Throughout the wet-end and finishing process, the tanner needs to know exactly what the end use of the leather will be. Whether it is to be used to make a pair of casual trainers, running shoes, football boots, climbing boots, riding boots, heavy duty shoes, fashion shoes, children's shoes or low cost sandals, the tanner needs to be aware of all the required performance features before deciding upon a process to prepare finished leather suitable for its intended purpose. This knowledge is essential in determining the choice of manufacturing procedures and of post-tanning products, dyestuffs, finishing products and systems that are compatible with the shoe finishing products needed to prepare the footwear for sale to the public. Modern water-based leather finishing products and systems now predominate almost exclusively. They can be used to upgrade the appearance and value of the leather by masking defects and providing colour enhancement, and are able to completely change the appearance of the leather in the process. High levels of resistance to wet and dry rubbing, wet and dry flexing and adequate adhesion of the finish is vital to enable ease of manufacture and ensure durability of the leather upper during the life of the shoe. The application of nitrocellulose top coats should be avoided when pvc sole units are used because of the risk of plasticiser migration which may discolour or cause tackiness of the pvc material. Instead, light fast acrylics and polyurethanes usually form the basis of leather coating formulations for general use for modern footwear applications. The tanner needs a great deal of information about the finished article to enable a leather to be crafted to meet its wear requirements. Caring in the shoe factory Leather is exposed to many different elements when it is processed through the shoe factory. After the initial pattern cutting, a marking pen may be used on the finished surface to identify cut components with a guide to stitching patterns. Steam will be used to moisturise the leather to enable the lasting operations to be performed and to enable the leather to be stretched without risk of the grain cracking before it is dried to form a permanent shape. Hot irons and even open flames may be used to smooth out the surface wrinkles. Various types of adhesives that are used to bond the interior components and sole unit may spill out onto the finished surface and these will subsequently need to be removed without affecting the finish. When passing through the many handling operations, the leather surface may become soiled and damaged. The original surface appearance of the leather as received from the tannery is commonly unrecognisable by the time the shoe is completely formed and the sole attached. These are some of the factors that necessitate the ensuing application of numerous finishing operations in the shoe factory to ensure that each pair of finished shoes is identical and appears pristine and elegant before being packed into the box for despatch to the retail outlet for sale to the public. The first of these finishing operations may involve cleaning the surface of the leather by wiping with a surfactant or a mild solvent mixture to remove dirt and other contaminants. When surface damage has occurred, the prepared surface may require a swab coat of primer or filler to restore its uniformity prior to application of a top coat that will protect the surface and enhance its appearance and handle. Between finish coat applications, the upper is often polished on a rotating cotton wheel to improve smoothness and avoid the need for applying a heavy finish coating. When the finished leathers have been produced to create special effects such as 'brush-off' or 'burnishing', special abrasive and polishing waxes are applied to the polishing wheels to help remove contrasting top coats or to darken the surface and create antique effects. The choice of both shoe and leather finishing products that are compatible is vital to ensure that an acceptable level of adhesion and flexibility of the total finish system is to be achieved, otherwise there could be problems during wear such as peeling of the shoe finish and white creasing in the vamp and other flexed areas. The tannery also needs to be aware of the style of footwear that is to be made from particular finished leathers so that the correctly controlled use of cross-linkers and silicones formulated into the top coats can be considered. A highly cross-linked finish is likely to be resistant to recoating and should be avoided. A simple test using adhesive tape will clearly demonstrate whether there is sufficient bonding of the shoe dressing and simple flex tests will identify poor inter-coat bonding between the various layers of the finish. Although they give superior performance, water-based shoe finishes require longer drying times than solvent-based alternatives which means that care needs to be taken to ensure that each coating layer is adequately dried prior to the application of subsequent coats. There are many different possibilities for processing and finishing both the leather and the shoes themselves which means that there is an obvious need to consider the choice carefully to ensure the resulting footwear will stand up to normal wear expectations and aftercare methods adopted by the consumer. Caring at home The traditional way of caring for footwear in the past was the use of shoe polish based on a wax that was available in either black, clear or brown. When white shoes became popular, a white-pigmented version also became available. When footwear became heavily soiled, this was removed either with a blade or by washing with a wet cloth and putting aside to dry. The wax was lightly applied using either a soft bristle brush or a soft sponge and then buffed to a shine with a soft cloth. The military applied the wax quite heavily using a cloth and then buffed to a high gloss shine. A time consuming job! There still remains a need to care for the leather uppers during use, whatever their application, and a complete range of modern leather dressings has been developed to be applied to specific types of leather with a view to maintaining the original freshness and protective properties. These can range from simple transparent creams and waxes formulated to remove surface soiling and restore shine, through pigmented wax preparations that camouflage surface damage and sprays containing perfume to detract from the effects of dermatosis, to high tech, aerosol applied silicone water repellents that minimise water absorption and retain the natural character of the leather upper. Modern attractive packaging of these products enables quick and easy application without mess and avoids the tedium of hard rubbing to produce a shine. This is now an essential feature and has to be designed into the products to make the care of footwear more attractive than the alternative - which is wearing shabby footwear that does not perform to the original promise of the shoemaker! Final comment In present times when almost everyone lives the disposable lifestyle, it is very important that manufacturers are not allowed to get away with making products that are designed to wear our prior to the end of a normal life expectancy. Having said that, the statutory right to complain should not be abused when a product is deemed not to perform to expectations. Obsolescence is designed and manufactured into many products of this age but the longevity of most quality products can be increased with attentive maintenance and a little care. To this effect, the products and technology are available to make high quality leather, high quality leather footwear and high quality aftercare products that will enhance the lifespan of footwear. With a minimum of time, effort and a little pride, the lifespan of leather products can be prolonged without compromise.