There is a great deal of conflicting information on leather care being put out by leather experts themselves who use baffling pseudo scientific techno speak as another marketing ploy, which makes it difficult to find a definitive, unbiased answer. Here is one definitive truth –you are dealing with the leathers finish, not the hide itself.



The use of oils, replacement of fat liquor, oil-based conditioning, proteins or the adjustment of pH levels is totally unnecessary; the surface is a urethane that contains pigmentation (colour) it neither needs or benefits from any of the above



Leather Tanning Process



All cowhides are naturally oily, unfortunately, these natural oils are stripped away in the tanning process, which is the process that renders the hide invulnerable to decay and some equivalent oils must be re-introduced after tanning. This last tanning step, the replacement of oils, is called "fat liquoring." Over the centuries, a number of oils have been found that have a natural affinity for leather fibres.



Every leather tanner has his own, unique, blend of tanning oils. These 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.



Leather tanners are now using advanced, high quality, hydrophilic polymers and synthetic oils that meet very high specifications; these polymers are typically fully reacted with the corium (fibres) they are neither volatile nor migratory. Due to this very low migration adding subsequent oils and lotions is no longer necessary and can be detrimental. (See article “Fat Liquoring”)



Leather Hides



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 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.



The thickness of the corium increases with age, which is why calfskins are thinner, smoother and softer than the hides of mature animals. Hides from cows are smoother, thinner and softer than the hides of mature male bull hides which are thick, tough, course grained and very strong.



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



Leather Conditioning



Leather is the hide removed from a deceased animal and the tanning / curing processes used seal in the necessary oils during the fat liquoring stage, thereby ensuring that the fibres cannot nor, do they need to be fed. Hide foods are something again that can be used in the horse and saddle business or with the older Aniline type dyed leathers.



There are numerous leather conditioning products in the marketplace, and they generally have the same overall function: to preserve the aesthetics of leather. However this can be better accomplished by replacing moisture (hydration) lost through evaporation.



There is no correlation between the cosmetics used for skin care and how we look after finished leather upholstery, Proteins, Collagen, Lanolin, Oils and Aloe are used for human skin reconstruction and nutrition, finished leather is not like human skin, its dead and cannot be regenerated or revived.



[Finished leather is a very chemically complex material, and if the conditioning product is incompatible it can have a damaging effect; peeling and / or cracking of the finish, colour transfer ("crocking"), yellowing, and general degradation are some of the problems that can be caused by the application of an improperly formulated, incompatible leather treatment product] Leather Research Laboratory



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



Finished Leather



Isocyanate based ethyl carbamate (urethane) finished leather upholstery is used by 95% as OEM in modern automobiles. It comprises a multi stratum acrylic and polyurethane resin binder system covering over the leather hide; the top strata are the surface pigmentation (colour) and an abrasion resistant urethane is used to improve flexibility, fastness and adhesion to the leather, then two or three aqueous (water- based) pigmented base coat applications.



And then a clear aqueous (water- based) top coat is applied as the final stage of the finishing process, which usually includes additives to give it a soft feel (patina) and abrasion resistance, as well as a limited amount of ‘slide’ to assist in entering and exiting the vehicle



It also has micro-pores that allow evaporation and hydration (the passage of water vapour through a membrane or pore) they are not sealed per se. Oils are not compatible with water-based pigmented urethane coatings and their molecules are too large to permeate, so they remain on the surface to be removed by clothing



Modern tanning and coating processes leave leather dynamic and self-regulating with regard to the moisture content therein. Repetitive heat cycling causes the leather to lose moisture, resulting in the formation of creasing or surface cracks, which further leads to the leather shrinking; however the urethane remains stable, which may lead to delamination,



Three Step Leather Care



1. Clean - there are two cleaning-related factors that can cause your leather to wear prematurely. The first is dirt, and the second is oil, combined they become very abrasive, as dirt / grit and subsequent friction cause the finish to wear



2. Hydrated – 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.



3. Protected - is essential as it will protect the surface finish 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



Research



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.



This is a lot of technical information, which probably won`t interest many of you, but correct, commercially unbiased automotive leather care information is not readily available on the internet; so I trust this will help someone, somewhere in the future, who is researching finished leather.





Associated Articles



1. “Reference sources and bibliography used for leather articles” - http://www.autopia.org/forum/autopia...ml#post1474865



2. A Brief History of Leather - http://www.autopia.org/forum/guide-d...ml#post1463189



3. Leather Tanning Process - http://www.autopia.org/forum/guide-d...ml#post1455796



4. Leather Fat Liquoring and Conditioning - http://www.autopia.org/forum/guide-d...ml#post1462908



5. Leather Restoration / Renovation - http://www.autopia.org/forum/autopia...ml#post1479003



6. “Types of Leather Used in Automobiles” - http://www.autopia.org/forum/autopia...ml#post1474058



7. “Leather Surface Identification” - http://www.autopia.org/forum/guide-d...ml#post1451654



8. Various Leather Surface Conditions and Correction - http://www.autopia.org/forum/guide-d...orrection.html



9. Leather care products - http://www.autopia.org/forum/guide-d...ml#post1465895



10. Removing Stains from Leather - http://www.autopia.org/forum/guide-d...ml#post1468879



11. Proper Finished Leather Cleaning and Care - http://www.autopia.org/forum/guide-d...ning-care.html



12. Leather Conditioning - http://www.autopia.org/forum/guide-d...ml#post1454835



13. Using Oil-based Leather Care Products - http://www.autopia.org/forum/guide-d...ml#post1450942



14. Aniline Leather; Cleaning and Care - http://www.autopia.org/forum/guide-d...ml#post1455011



15. Perforated (Nappa) Leather; Cleaning and Care - http://www.autopia.org/forum/guide-d...ml#post1455017



16. Alcantara Cleaning and Care - http://www.autopia.org/forum/guide-d...ml#post1455020



17. “Leather Restoration” - http://www.autopia.org/forum/autopia...ml#post1479003