Microscopic view of Leather's Corium (Fibres)
Correct information regarding the care of leather is scarce, often contradictory, misleading, or simply wrong. Misinformation can lead to inadvertent damage to your vehicles leather upholstery; my goal is to present clear, concise, accurate information.
There is a great deal of conflicting information on leather care being put out by leather experts themselves who recommend the same products and techniques be used regardless of the grade or the finish applied or use baffling pseudo scientific techno speak as another marketing ploy.
After various meetings and discussions with leather tanners, their research and development teams, chemists and fat liquoring formulators and many leather care product manufacturers I’ve gained an understanding of this versatile material on both a practical and scientific level.
It had always confounded me that such a simple subject has been made into something so complicated. I have always thought that the more facts and information you have at hand the easier it is to judge what information you are being given. After all, how can you fully understand and properly use any product unless you have all the facts? In the final analysis; it’s your vehicle, your hard earned money, and your choice
Be cognizant that you’re dealing with the finished coating on the leather, not with the leather hide itself
Leather Tanning Process
Is the process which converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that when re-wetted (or wetted back) putrefy, while tanned material dries out to a flexible form that does not become putrid when wetted back.
The leather is hygroscopic (naturally absorbs and retains water), meaning it’s also susceptible to losing the moisture necessary to keep it pliant and soft. The denaturing process of leather tanning removes moisture from the hide; water-based products restore the lost moisture of leather hides to maintain its natural flexibility.
Leather, at the time of completion of the tanning, does not contain sufficient lubricants to prevent it from drying into a hard mass. Almost all light leathers need a greater softness and flexibility than is imparted by tanning. This is attained in the fat liquoring process by introducing oil into the leather so that the individual fibres are uniformly coated. The percentage of oil on the weight of leather is quite small, from 3-10 %. The precise manner in which this small quantity of oil is distributed throughout the leather materially affects the subsequent finishing operations and the character of the leather.
These fat liquoring formulas are closely held secrets, passed down through generations; this is the origin of the new car ‘leather smell’. This is one reason why one company's leather can have a totally different feel, fragrance, texture and softness from another company's product. Modern leather tanning methods; chrome tanning, seals the hides ‘locking in’ the necessary fats and oils
Every leather tanner has his own, unique, blend of tanning oils. These formulas are closely held secrets, passed down through generations; they are neither volatile nor migratory, this is the origin of the new car ‘leather smell’. This is one reason why one company's leather can have a totally different feel, fragrance, texture and softness from another company's product
Leather is the fibrous corium or structural part of animal skins as shown above in microscopic cross-section. For a material that is so versatile, stylish and practical you could be fooled into thinking it is an extremely complicated material...far from it.
There are basically just three main materials from which hides and skins are made: water 60-65%, protein 25-30% oil and fats 5-10%. The protein is mainly collagen (found in many cosmetics) and it is this collagen that is transformed into leather by the tanning process.
Raw hides have four main parts - an epidermis, grain, corium and flesh
Two of these layers, the epidermis (which is a thin protective layer of cells during the life of an animal) and the flesh are removed during tanning by a process called liming.
This leaves just the grain and the corium, the parts that are used for automotive leather upholstery .The grain layer is made of collagen and elastin protein fibres and its structure varies quite a bit depending on the age, breed, and lifestyle of the animal. The grain carries many distinctive marks such as insect bites, growth marks and wound scars giving the leather a unique appearance.
The corium is packed with collagen protein fibres, arranged in larger bundles and interwoven to give the structure great strength, excellent elasticity, and durability. In the tanning process these fibres and impregnated with collagens and polymers that are designed to hold them together and keep them supple. Much of the suppleness of leather comes from its moisture content. After tanning the skin is protected with a thin pigmented (colour) urethane and then a clear topcoat.
Automobile Interior Environment
The interior environment of an automobile can be extremely demanding on any material used. Temperatures range from hot dry summer days to freezing nights. Both high and low humidity, even air conditioning that cools, but also dries. Leather's greatest enemies are; sun, heat, body oils, perspiration (that contains urea as well as organic salts and acids) and body heat, which causes acids to become more aggressive and alters the viscosity of oils, allowing them to permeate the leathers finish, and ultra violet radiation (UV), which dries the hide, fades the colour by bleaching, and can cause the leather to fail by drying out the fibres causing the urethane and/or the hide to crack.
Vehicle upholstery leather must allow hydration (transpiration and evaporation of moisture); otherwise, it will become less supple and the finish will be subject to cracking.
Hydration is simply the replacement of moisture and can be introduced via any perforated areas or places where the leather is joined together with stitching. These punctures in the surface coating are natural release areas where the leather begins to lose its moisture, especially in hot/dry environments.
Definition [: to supply water in order to restore or maintain fluid balance:]
When leather tanner’s talk about conditioning leather they are referring to its moisture content, re-hydration is used to restore or maintain fluid balance (transpiration and evaporation of moisture); not the replenishment or replacement of the fat liquoring, oils and/or waxes.
Moisture balance is a sine qua non (an indispensable and essential action) in leather care. Leather naturally absorbs and retains moisture vapour, meaning it’s also susceptible to losing the moisture necessary to keep it pliant and soft.
One of its major attributes is its ability for transpiration; allowing the movement of moisture back and forth (evaporation and hydration), which it does even better than wool.
This means not just its permeability to air but its permeability to water vapour, on the other hand, whilst it absorbs water vapour it doesn't readily absorb liquid, so a light rain will not harm it and a damp cloth can be used to keep it clean, however, the introduction of any solvent-based products accelerates aging of the leather.
Water-based products to a certain extent hydrate finished leather, more so on perforated leather. Water molecules are smaller than the micro pores in urethane so it can permeate the finish in vapour form. This is essential to transpiration (evaporation and hydration) to maintain a moisture balance as well as the suppleness and leathers natural flexibility, keeping finished leather at its optimum physical performance level, along with softness and strength
Ensure that the surface of the finished leather is clean and dust-free. Fill a fine mist atomizer spray bottle (Kwazar Mercury Pro) with distilled water; lightly mist the surface and then using a damp 100% cotton towel wipe the surface
Water damage due to spills is not, typically, a major cause for concern with automotive leather upholstery. A little water won’t hurt leather at all (See hydration) and most leather products have a protective layer that gives you enough time to clean up water spills before it can permeate the surface. When water does damage leather, it usually just makes the leather stiff.
‘Cardboard hard leather’ is certain indication that the leather has been allowed to dehydrate. The corium is packed with collagen protein fibres, arranged in larger bundles and interwoven to give the structure great strength, excellent elasticity, and durability.
In the tanning process these fibres and impregnated with collagens and polymers that are designed to hold them together and keep them supple. Much of the suppleness of leather comes from its moisture content. After tanning the skin is protected with a thin pigmented (colour) urethane and then a clear topcoat.
When corium fibres lose moisture they shrink when they are hydrated with water moisture they swell. The best way to care for finished leather and to keep wrinkles to a minimum is to keep the leather properly hydrated and avoid, as much as possible, these shrinking and swelling cycles. Keeping leather hydrated only requires a regular wipe down with a damp cotton towel.
To restore the suppleness to finished leather apply Leather Master™ Soft Touch to a clean surface - this is not a conditioner per se but is used to improve and maintain the tactile feel and lustre (Patina) by rehydration and to ensure the leather remains matte, soft and supple.
Apply a small amount to dry 100% cotton micro fibre towel, allow to dwell for 20-30 minutes and then wipe the surface with a dry 100% cotton micro fibre towel. For revitalizing older leathers and also to improve the feel of stiff leathers it’s better to apply several thin layers than a heavy application
The age and general condition of your leather and its environment will determine how often it should be hydrated. The recommended frequency for hydration is a function of the environment. For example, in an automobile, the head rests and top of the rear seat backrests tend to dry out very quickly due to direct, prolonged ultra violet (UV) radiation exposure.
Ideally, it should be initially thoroughly cleaned and hydrated so that it's in as best condition as possible and then simply regularly maintained to keep it in that condition.
A regime of monthly hydration of leather in hot, arid climates and the southern states is de rigueur; Florida, Texas, and Arizona, especially during the summer months, would not be out of line. In a northern climate or during winter months the interval between hydrations could be extended 60 to 90 days.
It should be vacuumed and maintained weekly or monthly depending on the usage of the vehicle and owners requirements.
Rain Ingress (or excess water) Damaged Surfaces
Rain ingress by inadvertently leaving a moon roof, convertible top or vehicles windows open during a rain storm will very likely soak the leather seating and perhaps the carpets. The damage would depend on how long it's exposed to water, restoration is important because it may become a breeding ground for mold and mildew. Left for a couple of weeks your whole interior would probably have to be replaced.
There are no leather finishes that are water proof. Leather hides used for automotive upholstery consist of approximately 45 square feet, that are stitched together to form a covering. The thousands of stitch holes allow any standing water to be absorbed and migrate laterally under the urethane finish. The perforated leathers used on many BMW, Mercedes-Benz, Porsches and other cars also allow standing water to permeate the urethane.
Leather that has been soaked in water may become brittle and may be ruined due to the formation of water mark stains and blemishes. Water damage restoration for leather is very manageable using the correct products and methodologies. When leather becomes soaked or wet, the best way to dry it is to use clean, dry towels to wipe away the water. Never dry leather using a heater as this will cause the leather to shrink rapidly, causing further drying and cracking.
Finished leather (urethane pigmentation) is water resistant, which means if you spill or allow liquid onto the surface and clean it right away it should not cause problems. Damage to the electronics that are under the seats (seatbelt sensor, seat positioning motor, air bag sensors, and etc) may be a cause for concern.
Obviously, the amount of damage could be lessened dependent upon how quickly action was taken. If you saw it immediately, and got it home quickly and dried it out using towels to soak up the rain water, most things would be okay.
Avoid flexing or bending the leather while you are restoring it because leather is weakened when the fibres are dry and it may crack.
Wet a towel with warm water, wring out excess. Proceed to wipe the leather to remove any dirt and moisten the surface. If you are working on a large item, do one section at a time so you can apply Leather Master™ Soft Touch (ex Vital) while the surface is still moist. This is not a conditioner per se; it contains polymers in an aqueous emulsion and is used to improve and maintain the tactile feel and lustre by rehydration and to ensure the leather remains matte, soft and supple.
Apply a small amount to a clean, damp 100% cotton micro fibre towel, use a circular motion and slight pressure to ensure the product permeates the dried-out pores, but do not push hard enough to damage the leather. Allow 20-30 minutes dwell time; unless the damage is severe, it should soften up after you massage it for a few minutes and then wipe the surface with a dry 100% cotton micro fibre towel.
Although water (hydration) is good for leather and is what keeps it in good condition generally when its fibres become over soaked they swell and become deformed. When they dry they may not shrink back and revert to their original form and so become more brittle and distorted. Unfortunately, at this stage, it may be impossible to rectify.
With leather, it is much easier to practice prevention than it is to try to resolve major challenges after the fact. Leather Protection will also work to remove small surface scratches on finished leathers. In general, Leather Protection Cream is used as a final step in combination with most of the Leather Master products.
This is essential as it will protect the surface finish (Leather Master™ - Protection Cream, a Scotchgard™ type, water-based product) as a sacrificial layer; this way you are not actually cleaning the Leather's original surface, but cleaning from the surface of the protection. It also makes dirt easier to clean off
The polymers penetrate the surface of finished leather and cross-link to form a durable protective film that is breathable, allowing transpiration and keeps the leather supple. Being aqueous (water- based) it restores moisture to finished leather and provides a protective sacrificial barrier against all kinds of soiling, water, oil, alcohol-based stains and perspiration marks, so you are cleaning the protective layer
2. “Leather Articles Hyperlinks”
3. “Hydration of Finished Leather”
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