Section through finished leather - Diagram by Advanced Leather Solutions
Be cognizant that you’re dealing with the finished coating on the leather and not with the leather hide itself
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 use baffling pseudo scientific techno speak as another marketing ploy, which makes it difficult to find a definitive, unbiased answer. It had always confounded me that such a simple subject has been made into something so complicated.
After various meetings and discussions with leather tanners, fat liquoring formulators, their chemists and many leather care product manufacturers I’ve gained an understanding of this versatile material on both a practical and scientific level.
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
Original Equipment Manufacturers (OEM) Technology
Automotive equipment technology is becoming more and more complex requiring educated and skilled technicians to work on them. As the materials used are constantly changing we must maintain our knowledge base and utilize the correct products and application methodologies to keep up with emerging technologies. It is very important to be able to recognise the various finishes and materials used as they all require different methodologies and products for proper care and maintenance.
A competent detailer never stops learning; knowledge of new technology and application methods also make detailer’s an asset to both a company and its clients and increase the value of the services offered. A detailer should know how to tell the difference between -
a) Single stage paint and a base coat clear coat paint system and be able to match the correct products to each system
b) Coated and uncoated aluminium wheels and what products to use for each finish
c) Finished and uncoated leather and the appropriate care products to use
Diagnosis is the key, not guess work. Before deciding on what products to use, you need to ascertain the grade of leather and the type of leather finish applied.
There are a few different types of leather and several types of finishes applied to the leather used for vehicles upholstery. There are also a myriad of leather care products available, which need to be used in accordance to the type of and finish used for your vehicles upholstery
Automotive leather is a rather difficult category to define as OEM descriptions of leather finishes vary, often incorrectly from that of leather industry manufacturer’s descriptions. Automobile manufacturers have blurred the distinguishing lines on what exactly constitutes leather and the ambiguity of the information provided by leather care vendors make the selection of the correct products for the types of finished leather used in automobiles very difficult.
Prior to 1939 leathers produced were solely vat dyed. Usually these colors faded quickly and developed into strange shades of greens or browns after exposure to the sun. Although the surfaces did not crack and chip as badly, the leather still became dry and stiff.
After 1945 new technology created new demands and brighter colors quickly became popular with the availability of nitrocellulose resin emulsion lacquers. Leathers that were vat dyed were now surface coated as well. In the early 1980’s nitrocellulose lacquers gave way to the resin-base dyes in use today.
Before 1980 most automotive leather upholstery used was high quality top grain full grain leather with a pigmented solvent-based Nitrocellulose lacquer coating and their unstable plasticizers would easily migrate in the heat from sun exposure and again create 'fogging' on the internal surfaces of the windows. As a result of this plasticizer migration the use of oil-based products that contained solvents to keep them from becoming brittle and cracking, creams, waxes and oils were needed in aftercare products to try and bring the suppleness back into the leather by applying an oil-based conditioner
This can be accomplished by covering the seats with a plastic bag to help retain the heat and them leave overnight will ensure the oils permeate the lacquer and reach the leather hide. This process can also be used for equestrian tack; bridles, harnesses’, saddle and leather chaps and riding boots.
This nitrocellulose resin conditioning methodology for some reason has been carried over to modern finished leather. Even though urethane’s only requirement is to be kept clean and hydrated, it doesn’t require conditioning. Products such as leather (Saddle) soaps, oil-based Conditioners, Neat-foot oil, Mink oil and Connolly Hide Food still prevail as top sellers, albeit most are made for equestrian tack. These are very different leathers with drastically differing care requirements. The exact reason for this type of misapplication is unclear.
It’s possible that there is an association with old world quality (i.e. European automobiles with unfinished leather upholstery and real burl wood interiors) with these types of products, despite the fact that the automotive industry has been using aqueous (water- based) urethane covered pigmented leather since 1980.
Automotive OEM technology is becoming more and more complex requiring educated and skilled technicians to work on them. As the materials used are constantly changing we must maintain our knowledge base and utilize the correct products and application methodologies to keep up with emerging technologies.
Automobile manufacturers have blurred the distinguishing lines on what exactly leather is. There are many so-called ‘leathers’ that are actually the bottom split (the fibrous part of the hide) which are covered with a vinyl or urethane coating. Diagnosis is the key, not guess work. Before deciding on what products to use, you need to ascertain the grade of leather and the type of leather finish applied
The leather used for automotive upholstery has a finish applied that comprises a polyurethane protective layer and an abrasion resistant topcoat.
Polyurethane is a polymer composed of a chain of organic units joined by Ethyl carbamate (urethane) links; the polyurethane used is categorized as an elastomers; it has elastic properties while maintaining some rigidity.Polyurethane is semi-permeable and has micro pores that allow hydration (transpiration and evaporation of moisture); otherwise it would become less supple and the finish will be subject to cracking.
Be cognizant that the leather and finishes used for automotive upholstery varies from leather industry standard descriptions and although the names are similar the type of leather, pigmentation and finish are often very different. Si it is very important to be able to recognise the various finishes and materials used by OEM’s as they all require different methodologies and products for proper care and maintenance.
Automotive model ranges use different materials for their vehicles interiors; leather upholstery like Aniline Immersion Dyed, Aniline Micro Pigmented, (Urethane) Finished, Artificial leather such as MB-Tex and unfinished materials like Synthetics and Alcantara, and sometimes combinations of products (Alcantara seat inserts on leather seating) as well as various grades of leather hide, full-grain, top-grain and split –grain (which is protected with urethane) all of which require different products and applications methods.
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
. Automotive 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.
Unfinished vs. Finished leather
a) Unfinished leather - the appeal of this type of leather is its initial "natural" look and the soft, supple texture. The downside is aesthetic vulnerability; due to the porous nature of untreated leather, it stains easily and it is sensitive to ultra violet (UV) light, which means that the colour is subject to photochemical degradation (bleaching, (fading), discolouration chalking, brittleness and cracking) all indications of UV deterioration. The porous nature of unfinished leather will allow a water- or oil-based solution to permeate the leather.
b) Finished or micro pigmented leather - is commonly used for automobile as these resins create a film that protects the leather. The water-based polyurethane pigmented (colour) coat and the clear topcoat provides abrasion and stain resistance. This type of leather finish is the most durable and easiest to care for but tends to be stiffer than both unfinished and micro pigmented leather. When Ford first introduced its King Ranch leather in their F-Series trucks it had unfinished leather, later they adopted a micro pigment type finish
Using advanced micro pigments this finishing technique makes the finish rigorous enough to stand up to the conditions it would be subjected to in an automobile. Generally speaking micro pigment style leathers come in very earthy natural colours, incorporating a small quantity of pigment (a thin clear sealant that provides a uniform colour and affords some protection) but not so much as to conceal the natural characteristics of the hide so it will still retain the soft hand of Aniline leather. This type of leather is also used for perforated leather finishes.
Now virtually 95% of leather in domestic (American) and Imported (Asian) vehicles use finished (polyurethane coated) upholstery. Among European car makers aniline and recently semi-aniline (micro pigmented) leather upholstery is still much more common than with domestic models, but urethane finished leather is becoming more prevalent
Automobile model ranges use different materials for their vehicles interiors; there are also various finishes applied -
· Aniline Leather (Immersion Dyed)
· Semi-aniline (Micro pigment) leather
· Finished leather
As well as various grades of leather hide, full-grain, top-grain and split –grain, along with artificial leather such as MB-Tex and unfinished materials like Synthetics and Alcantara, and sometimes combinations of products (Alcantara seat inserts on leather seating) Using any product not specifically designed for your leather finish can cause staining and permanent damage.
Cross section through leather hide
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 [Latin term for the dermis] or skin layer, 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 collagen's that are designed to hold them together and keep them supple after which they are sealed, these polymers are neither volatile nor migratory, rendering the use oil-based conditioner a mute point
Leather, at the time of completion of the tannage 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 tannage. 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.
Proper lubrication or fat liquoring greatly affects the physical properties of break, stretch, stitch tear, tensile strength, and comfort of leather. Over lubrication will result in excessive softness and raggy leather in the bellies and flanks. Under lubrication, or improper penetration, results in hard bony leather that may crack in use.
To allow a small amount of oil to be spread uniformly over a very large surface of the leather fibres it is necessary to dilute the oil.
Although this could be done with a true solvent such as benzene, it is cheaper, safer and more convenient to use the method of emulsification. In an emulsion with water, the oil is dispersed in microscopically small droplets, giving it a white, milky appearance.
It is important that the oil drops in water should remain as an emulsion until they penetrate the leather, and should not separate out as large drops or as a layer of oil, which could not penetrate the leather fibre and would only give a greasy surface layer.
The other critical factor is moisture (re-hydration) any leather is going to lose its moisture in hot ambient environments. Much of the suppleness of leather comes from its moisture content, which is the reason maintain the moisture content of the grain layer is so important. When leather tanners talk about leather conditioning they specifically mean replacing its moisture content (re-hydration). After tanning the skin is protected with pigmented (colour) polyurethane and then a clear topcoat.
The leather used for automotive upholstery is finished leather comprising a polyurethane protective layer and an abrasion resistant topcoat. Polyurethane is a polymer composed of a chain of organic units joined by Ethyl carbamate (urethane) links
Polyurethane (urethane) 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, although some may enter via stitching, usually it remains on the surface to be removed by clothing
Since the leather hide has a pigmented urethane layer and clear topcoat finish, when treating the leather, so you are in fact dealing with a urethane (to all intents and purposes, a ~150 µ (micron) thick plastic surface coating, about the same thickness as automobile clear coat paint; that simply needs to be kept clean and hydrated…it really is that simple.
Topcoat - extremely hard wearing water-based clear polyurethane is used to improve abrasion resistance and colour fastness, making the surface much easier to clean and less prone to staining, while increasing resistance to perspiration, grease and oil. It greatly increases surface durability and also improves surface texture giving it a smooth, soft and silky feel.
It also has micro-pores that allow transpiration, i.e. evaporation and hydration (the passage of water vapour through a membrane or pore) they are not sealed per se. Urethane pigmented finished leather doesn't readily absorb liquids because of the protective properties of the finish making for easier clean-up.
A simple test – place a drop of moisture on the surface of the leather - if it soaks into the leather you have unfinished leather (sometimes called aniline style) If there is a very light color or clear coat on top of aniline-dyed leather, it is often referred to as “semi-aniline.” Semi-aniline leather offers modest protection while retaining much of the aesthetic beauty of unfinished aniline-dyed leather but still remain absorbent to moisture. If the moisture sits on the surface and does not soak in and darken the material you have finished leather.
TOGWT® Autopia Detailing Wiki Articles
1. “Unfinished leather” - http://www.autopia.org/forum/autopia-detailing-wiki/145381-unfinished-eather.html#post1543547
2. “Proper Finished Leather Cleaning and Care” - http://www.autopia.org/forum/guide-detailing/136421-proper-finished-leather-cleaning-care.html