togwt
The Old Grey Whistle Test
Research
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, their 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.
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
Many of the following statements are controversial and are polar opposite of popular leather care practices recommended by leather care product manufacturers. I've found that some leather care myths are deliberately perpetuated by the industry, especially those on the use of oil-based leather conditioners and others are just common errors of judgment.
Modern automotive finished leather upholstery used by 95% of OEM is a multi strata covering over the leather hide; pigmentation (colour) and an abrasion resistant urethane. Finished leather s only requirement is to be kept clean and protected, urethane doesn’t require conditioning
[Fat liquor is not volatile nor migratory, so leather is not going to lose it. However, along with the fat liquor, the other critical factor is moisture. Any leather is going to lose its moisture in a hot car. Although leather seems dry, it is not. Of course too much moisture quickly leads to mould and mildew problems, so soaking it down is not reasonable. Ideally, exposure to humid atmosphere will help balance the effect of over drying on hot days. Leather is very dynamic with respect to moisture content, meaning moisture comes and goes easily under normal circumstances....] American Leather Chemists Association
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.
All cowhides are naturally oily, unfortunately, these natural oils are stripped away in the tanning process (tanning is a process using a water vat and chromium salts to preserve hides and prepare them to absorb dyes) and some equivalent oils must be re-introduced after tanning. This 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 the generations.
In almost all situations fat liquors are designed to be applied to leather in the form of an aqueous emulsion that is ‘oil in water emulsion’. A fat liquor emulsion can be of various particle sizes. If the emulsion is coarse it will have a particle size of around 0.1 µ (micron) and will have a milky appearance. In this situation, the penetration of these fat liquors is restricted to the surface of the leather. If the particle size is around 0.03µ then the emulsion is translucent, and because of the smaller size these can generally penetrate more deeply into the fibre structure. Emulsions of 0.005µ are classified as micro-emulsions; they are relatively clear and give good penetration
Note: 0.3 µ (micron) is the largest particle size that can fit through a HEPA filter
In the fat liquoring process, both the penetration and the fixation of fatty matter take place. In order to optimise penetration into the leather structure, fat liquor must be emulsified in water and added to the processing vessel. The mechanical effects caused by the drum rotation, the surface tension and the capillary action of the hides, all promote penetration of the fat liquor into the structure. Fixation of this fat liquor is achieved by adding acid products at the end of the process.
Fat liquoring is usually carried out in a drum at the highest temperature practical for the type of leather, or about 113.oF (45° C) for vegetable tanned leather and 140-150.OF (60 to 65° C) for full chrome tanned leather. Fr the best results ideal rotational speed of the fat liquoring drum should be around 12-16 RPM for 30 to 40 minutes. After drumming, the leathers are usually struck out on the flesh side, carefully set out to smooth the grain, nailed or toggled out flat to dry, or paste dried. Strict control over the initial pH of the fat liquoring bath & the final pH of the exhaust bath should be maintained so as to achieve uniform fat content and fat distribution in leather and to avoid many fat splitting problems. Source leatherbiz.com Technical Articles Library
Modern fat liquors are technically advanced using high quality specially processed natural and synthetic oils that meet very high specifications. These are typically fully reacted to the fibre structure, and as a consequence only minimal amounts can migrate out of the leather. Because of this low migration continually adding creams and lotions to replace lost oils is therefore no longer necessary.
Leather Conditioning
Modern automotive finished leather upholstery used by 95% of OEM is a multi strata covering over the leather hide; pigmentation (colour) and an abrasion resistant urethane. Finished leather s only requirement is to be kept clean and protected, urethane doesn’t require conditioning
The following are factual details that leather care manufacturers would rather you didn’t know.
[There are numerous leather conditioning products in the marketplace, and they generally have the same overall function: to preserve the performance and aesthetics of leather. This can be achieved by:
• Replenishing the lubricating oils ("fat liquors") that have been oxidized and otherwise lost during its lifetime, and/or;
• Replacing moisture lost through evaporation.
However, leather is a very chemically complex material, and if the conditioning product is incompatible with it in any way, it can exert a damaging effect:
Finish peeling, finish cracking, color transfer ("crocking"), yellowing, and general leather 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 leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. The only 'conditioning' required for finished leather upholstery is hydration; oil-based products cannot permeate the finish leather (urethane pigmentation and / or covering) that is used in 95% plus of modern automobiles.
Modern leather needs to be kept hydrated with moisture to ensure the leather remains flexible and maintains its soft tactile feel. This is done by regularly wiping the surface with a damp 100% cotton micro fibre towel and by using aqueous (water- based) leather care products. There is no reason to use oil-based leather care products to condition or feed leather hides
Aqueous (water- based) products are able to permeate deep into the hide, unlike oil, due to its larger particles, whereas water particles are smaller than both oil and the molecules of urethane, which enables aqueous (water- based) products to permeate and provide hydration, which is essential for suppleness recovery.
Particulate size - you can tell how small the emulsion droplets are and in some cases how concentrated an emulsion is by its colour. Opaque white emulsions typically have a large particle size, while faintly opaque or pearlescent emulsions typically have a small particle size approaching 1µ or less.
Water - unlike other organic or hydrocarbon-based solvents, is non-flammable, odourless, non-toxic and non-sensitizing to the skin and it doesn’t impart a greasy or tacky feel to the surface of the leather
I have discussed this issue with many people in both the leather tanning and leather care products industry and some specialised industrial chemists who have worked in the leather manufacture and care industry for 35 plus years. As specialists in leather care they had a much better understanding of what the ideal product is for maintaining finished leather surface used in automotive leather upholstery and I asked the following questions.
(a) How much conditioner will get through the cross-linked urethane coating on the leather?
(b) A chrome tanned leather hide is sealed at the tannery and then pigmented; what could a conditioner do for the hide?
We discussed the product s that are currently being used and the consensus was that many of the products simply were not suitable for the current finishes used for automotive leather
I looked at a detailing care product vendor site and found nine pages of leather care products, mostly expensive oil-based leather ‘conditioners’ this could be the reason they ignore an appropriate care product for the upholstery material actually used for automotive (finished leather) upholstery.
1. How much conditioner will permeate the urethane top coat on a sealed pigmented leather hide? Chrome tanned leather hide is sealed at the tannery and then pigmented; what could a conditioner do for the hide?
2. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will travel laterally compromising the resin binder system which will delaminate from the hide releasing its adhesive bond. It will then be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering
3. The complex tanning process of chromed tanned hides results in the fat liquoring and oils necessary to keep the hide soft and pliable being locked in, this is further sealed by a durable polyethylene covering to protect the hide from abrasion from clothing as well as the dust / dirt introduced by the vehicle’s AC system.
4. The complaint that most leather conditioners are "greasy" is typically attributable to the use of Lanolin. On most leather conditioners the containers label warns against its use on steering wheels as it will make them slippery and unsafe. The oils cannot permeate the leather and therefore remain on the surface; the same thing will apply to seating surfaces; the problem will be exasperated as the oil will attract dirt/grime to the surface
Many so called leather conditioners utilize chemical solvents in order to facilitate penetration of the oils into the urethane covering or the pigmented leather. Most covered leather finishes are water -based and so any solvent or alcohol can begin to cut through them, even if you go over it and you see no colour come off, you have probably compromised the clear protective top coat and possibly the leather’s pigmentation (colour).
Solvents will soften the protective covering, which can get tacky very quickly, attracting abrasive dust/dirt and will eventually wear through as it does not have the durability found in the topcoat. What happens when the solvents vaporise - polish and many surface protection products are formulated with oils to enhance the surface or to nourish leather surfaces, neither of which is necessary?
Not all conditioners are alike; some are aqueous (water- based) as opposed to oil-based. Some contains about 90% water, when applied to the leather surface, it appears to “soak in� (hydration) leaving only a very thin film of oil to benefit the surface lubrication (driver or passenger entry / exit). (See also Oil and oil-based Products)
A urethanes fibre structure will stretch in all directions with no particular grain or stress pattern. The urethane surface coating will not withstand multi directional stress, however, and when it’s flexed or stretched continuously in the same place the surface coating develops minute cracks. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will compromise the resin binder system and delaminate from the hide releasing its adhesive bond, and it will be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering
In summary, an aqueous micro emulsion is readily absorbed into the fibres and provides lasting and effective lubrication without migration, while re-hydration leaves leather feeling silky soft and pliable.
Feeding Leather
[Zymöl Treat Leather Conditioner is a solvent-free, banana-oil and collagen-based feeding product that releases trapped solvents and restores moisture to keep your leather looking, feeling, and smelling like new. Helps to reduce the aging process in leather upholstery and trim] Zymöl Website
Older (50 and 60’s) automobile upholstery leather and exterior paint was finished with Nitrocellulose lacquer and required oils for it to remain flexible otherwise it would crack. This is where the ‘feeding’ paint / leather comes from
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 is no correlation between how we look after our own skin and how we look after finished leather upholstery, Proteins, Collagen, Lanolin and Aloe are used for human skin reconstruction and nutrition, leather is not like human skin, its dead and cannot be regenerated or revived.
Many leather treatment theories have grown up around the fact that you need to moisturise skin and so this is wrongly transferred to the care of finished leather, especially when you consider that it has a urethane pigmented coating
Moisture Content
Leather is hygroscopic and so moisture is the most important element (median 15 %) in the care of leather; all changes in leather are due to moisture differences. Too little moisture (< 10%) will cause the leather to become hard and inflexible, too much (> 20 %) and it may the fibres to swell and may cause mould formation.
Leather's major attribute is its ability to breathe, which it does even better than wool. This means not just its permeability to air but its permeability to water vapour, so allowing the absorption of perspiration and warmth. Thus it feels warm in winter and cool in summer, yet doesn't become hot and sticky.
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
Leather naturally absorbs and retains moisture, 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, introducing solvent-based products accelerates aging of the leather.
When leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. The only 'conditioning' required for finished leather upholstery is hydration;
The purpose of rehydration is to restore moisture lost through evaporation, so whatever the surface finish it has to allow the movement of moisture back and forth (evaporation and hydration) As leather is porous, it loses its moisture through evaporation at a rate dependent upon two variables; ambient humidity level, and heat. Where ambient conditions are very hot and / or experience very low humidity, finished leather will lose its moisture, which must be replaced.
The breathability of leather allows small particles of moisture to move back and forth through the leather and this is what keeps it in good condition. Once the moisture levels in leather drop due to evaporation or transpiration it becomes dry and brittle, to avoid this it needs to be re-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 sun exposure.
Why does leather feel dry or stiff? What actually dries out is the leather’s moisture, which then leaves the fat liquors stiffer and less flexible (hence the feeling of dryness or stiff leather)
Surface moisture constitutes approximately 10% of finished leathers moisture content, which is subject to evaporation and must be replaced to avoid dehydration. Most of the actual hide’s moisture content is provided by the tanner when the fat liquor introduced during the re-tanning process, which maintains the moisture of the corium fibre matrix, allowing them to remain flexible. This fat liquoring is sealed into the hide and under normal circumstances should not require any maintenance
Aqueous (water- based) products restore the lost moisture of finished leather and maintain its natural flexibility. When moisture is replaced the fibres will become flexible again and gives the leather a softer feel. Being in an enclosed space with little to no ventilation will exacerbate dehydration if the leather is subjected to very high temperatures and low humidity conditions the fat liquor oils introduced during the re-tanning process may become destabilised, leading to the finished leather becoming dehydrated.
Apply an aqueous (water- based) product (Leather Master Soft Touch (ex Vital) this is not a conditioner per se but it will revitalise leather that has become dehydrated. It is also excellent for improving the tactile feel of leathers. Apply to surface and allowing it to remain, renewing as necessary. And then apply an aqueous (water- based) protection
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, their 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.
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
Here is one definitive truth –you are dealing with the leathers finish, not the hide itself.
Many of the following statements are controversial and are polar opposite of popular leather care practices recommended by leather care product manufacturers. I've found that some leather care myths are deliberately perpetuated by the industry, especially those on the use of oil-based leather conditioners and others are just common errors of judgment.
Modern automotive finished leather upholstery used by 95% of OEM is a multi strata covering over the leather hide; pigmentation (colour) and an abrasion resistant urethane. Finished leather s only requirement is to be kept clean and protected, urethane doesn’t require conditioning
[Fat liquor is not volatile nor migratory, so leather is not going to lose it. However, along with the fat liquor, the other critical factor is moisture. Any leather is going to lose its moisture in a hot car. Although leather seems dry, it is not. Of course too much moisture quickly leads to mould and mildew problems, so soaking it down is not reasonable. Ideally, exposure to humid atmosphere will help balance the effect of over drying on hot days. Leather is very dynamic with respect to moisture content, meaning moisture comes and goes easily under normal circumstances....] American Leather Chemists Association
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.
All cowhides are naturally oily, unfortunately, these natural oils are stripped away in the tanning process (tanning is a process using a water vat and chromium salts to preserve hides and prepare them to absorb dyes) and some equivalent oils must be re-introduced after tanning. This 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 the generations.
In almost all situations fat liquors are designed to be applied to leather in the form of an aqueous emulsion that is ‘oil in water emulsion’. A fat liquor emulsion can be of various particle sizes. If the emulsion is coarse it will have a particle size of around 0.1 µ (micron) and will have a milky appearance. In this situation, the penetration of these fat liquors is restricted to the surface of the leather. If the particle size is around 0.03µ then the emulsion is translucent, and because of the smaller size these can generally penetrate more deeply into the fibre structure. Emulsions of 0.005µ are classified as micro-emulsions; they are relatively clear and give good penetration
Note: 0.3 µ (micron) is the largest particle size that can fit through a HEPA filter
In the fat liquoring process, both the penetration and the fixation of fatty matter take place. In order to optimise penetration into the leather structure, fat liquor must be emulsified in water and added to the processing vessel. The mechanical effects caused by the drum rotation, the surface tension and the capillary action of the hides, all promote penetration of the fat liquor into the structure. Fixation of this fat liquor is achieved by adding acid products at the end of the process.
Fat liquoring is usually carried out in a drum at the highest temperature practical for the type of leather, or about 113.oF (45° C) for vegetable tanned leather and 140-150.OF (60 to 65° C) for full chrome tanned leather. Fr the best results ideal rotational speed of the fat liquoring drum should be around 12-16 RPM for 30 to 40 minutes. After drumming, the leathers are usually struck out on the flesh side, carefully set out to smooth the grain, nailed or toggled out flat to dry, or paste dried. Strict control over the initial pH of the fat liquoring bath & the final pH of the exhaust bath should be maintained so as to achieve uniform fat content and fat distribution in leather and to avoid many fat splitting problems. Source leatherbiz.com Technical Articles Library
Modern fat liquors are technically advanced using high quality specially processed natural and synthetic oils that meet very high specifications. These are typically fully reacted to the fibre structure, and as a consequence only minimal amounts can migrate out of the leather. Because of this low migration continually adding creams and lotions to replace lost oils is therefore no longer necessary.
Leather Conditioning
Modern automotive finished leather upholstery used by 95% of OEM is a multi strata covering over the leather hide; pigmentation (colour) and an abrasion resistant urethane. Finished leather s only requirement is to be kept clean and protected, urethane doesn’t require conditioning
The following are factual details that leather care manufacturers would rather you didn’t know.
[There are numerous leather conditioning products in the marketplace, and they generally have the same overall function: to preserve the performance and aesthetics of leather. This can be achieved by:
• Replenishing the lubricating oils ("fat liquors") that have been oxidized and otherwise lost during its lifetime, and/or;
• Replacing moisture lost through evaporation.
However, leather is a very chemically complex material, and if the conditioning product is incompatible with it in any way, it can exert a damaging effect:
Finish peeling, finish cracking, color transfer ("crocking"), yellowing, and general leather 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 leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. The only 'conditioning' required for finished leather upholstery is hydration; oil-based products cannot permeate the finish leather (urethane pigmentation and / or covering) that is used in 95% plus of modern automobiles.
Modern leather needs to be kept hydrated with moisture to ensure the leather remains flexible and maintains its soft tactile feel. This is done by regularly wiping the surface with a damp 100% cotton micro fibre towel and by using aqueous (water- based) leather care products. There is no reason to use oil-based leather care products to condition or feed leather hides
Aqueous (water- based) products are able to permeate deep into the hide, unlike oil, due to its larger particles, whereas water particles are smaller than both oil and the molecules of urethane, which enables aqueous (water- based) products to permeate and provide hydration, which is essential for suppleness recovery.
Particulate size - you can tell how small the emulsion droplets are and in some cases how concentrated an emulsion is by its colour. Opaque white emulsions typically have a large particle size, while faintly opaque or pearlescent emulsions typically have a small particle size approaching 1µ or less.
Water - unlike other organic or hydrocarbon-based solvents, is non-flammable, odourless, non-toxic and non-sensitizing to the skin and it doesn’t impart a greasy or tacky feel to the surface of the leather
I have discussed this issue with many people in both the leather tanning and leather care products industry and some specialised industrial chemists who have worked in the leather manufacture and care industry for 35 plus years. As specialists in leather care they had a much better understanding of what the ideal product is for maintaining finished leather surface used in automotive leather upholstery and I asked the following questions.
(a) How much conditioner will get through the cross-linked urethane coating on the leather?
(b) A chrome tanned leather hide is sealed at the tannery and then pigmented; what could a conditioner do for the hide?
We discussed the product s that are currently being used and the consensus was that many of the products simply were not suitable for the current finishes used for automotive leather
I looked at a detailing care product vendor site and found nine pages of leather care products, mostly expensive oil-based leather ‘conditioners’ this could be the reason they ignore an appropriate care product for the upholstery material actually used for automotive (finished leather) upholstery.
1. How much conditioner will permeate the urethane top coat on a sealed pigmented leather hide? Chrome tanned leather hide is sealed at the tannery and then pigmented; what could a conditioner do for the hide?
2. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will travel laterally compromising the resin binder system which will delaminate from the hide releasing its adhesive bond. It will then be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering
3. The complex tanning process of chromed tanned hides results in the fat liquoring and oils necessary to keep the hide soft and pliable being locked in, this is further sealed by a durable polyethylene covering to protect the hide from abrasion from clothing as well as the dust / dirt introduced by the vehicle’s AC system.
4. The complaint that most leather conditioners are "greasy" is typically attributable to the use of Lanolin. On most leather conditioners the containers label warns against its use on steering wheels as it will make them slippery and unsafe. The oils cannot permeate the leather and therefore remain on the surface; the same thing will apply to seating surfaces; the problem will be exasperated as the oil will attract dirt/grime to the surface
Many so called leather conditioners utilize chemical solvents in order to facilitate penetration of the oils into the urethane covering or the pigmented leather. Most covered leather finishes are water -based and so any solvent or alcohol can begin to cut through them, even if you go over it and you see no colour come off, you have probably compromised the clear protective top coat and possibly the leather’s pigmentation (colour).
Solvents will soften the protective covering, which can get tacky very quickly, attracting abrasive dust/dirt and will eventually wear through as it does not have the durability found in the topcoat. What happens when the solvents vaporise - polish and many surface protection products are formulated with oils to enhance the surface or to nourish leather surfaces, neither of which is necessary?
Not all conditioners are alike; some are aqueous (water- based) as opposed to oil-based. Some contains about 90% water, when applied to the leather surface, it appears to “soak in� (hydration) leaving only a very thin film of oil to benefit the surface lubrication (driver or passenger entry / exit). (See also Oil and oil-based Products)
A urethanes fibre structure will stretch in all directions with no particular grain or stress pattern. The urethane surface coating will not withstand multi directional stress, however, and when it’s flexed or stretched continuously in the same place the surface coating develops minute cracks. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will compromise the resin binder system and delaminate from the hide releasing its adhesive bond, and it will be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering
In summary, an aqueous micro emulsion is readily absorbed into the fibres and provides lasting and effective lubrication without migration, while re-hydration leaves leather feeling silky soft and pliable.
Feeding Leather
[Zymöl Treat Leather Conditioner is a solvent-free, banana-oil and collagen-based feeding product that releases trapped solvents and restores moisture to keep your leather looking, feeling, and smelling like new. Helps to reduce the aging process in leather upholstery and trim] Zymöl Website
Older (50 and 60’s) automobile upholstery leather and exterior paint was finished with Nitrocellulose lacquer and required oils for it to remain flexible otherwise it would crack. This is where the ‘feeding’ paint / leather comes from
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 is no correlation between how we look after our own skin and how we look after finished leather upholstery, Proteins, Collagen, Lanolin and Aloe are used for human skin reconstruction and nutrition, leather is not like human skin, its dead and cannot be regenerated or revived.
Many leather treatment theories have grown up around the fact that you need to moisturise skin and so this is wrongly transferred to the care of finished leather, especially when you consider that it has a urethane pigmented coating
Moisture Content
Leather is hygroscopic and so moisture is the most important element (median 15 %) in the care of leather; all changes in leather are due to moisture differences. Too little moisture (< 10%) will cause the leather to become hard and inflexible, too much (> 20 %) and it may the fibres to swell and may cause mould formation.
Leather's major attribute is its ability to breathe, which it does even better than wool. This means not just its permeability to air but its permeability to water vapour, so allowing the absorption of perspiration and warmth. Thus it feels warm in winter and cool in summer, yet doesn't become hot and sticky.
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
Leather naturally absorbs and retains moisture, 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, introducing solvent-based products accelerates aging of the leather.
When leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. The only 'conditioning' required for finished leather upholstery is hydration;
The purpose of rehydration is to restore moisture lost through evaporation, so whatever the surface finish it has to allow the movement of moisture back and forth (evaporation and hydration) As leather is porous, it loses its moisture through evaporation at a rate dependent upon two variables; ambient humidity level, and heat. Where ambient conditions are very hot and / or experience very low humidity, finished leather will lose its moisture, which must be replaced.
The breathability of leather allows small particles of moisture to move back and forth through the leather and this is what keeps it in good condition. Once the moisture levels in leather drop due to evaporation or transpiration it becomes dry and brittle, to avoid this it needs to be re-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 sun exposure.
Why does leather feel dry or stiff? What actually dries out is the leather’s moisture, which then leaves the fat liquors stiffer and less flexible (hence the feeling of dryness or stiff leather)
Surface moisture constitutes approximately 10% of finished leathers moisture content, which is subject to evaporation and must be replaced to avoid dehydration. Most of the actual hide’s moisture content is provided by the tanner when the fat liquor introduced during the re-tanning process, which maintains the moisture of the corium fibre matrix, allowing them to remain flexible. This fat liquoring is sealed into the hide and under normal circumstances should not require any maintenance
Aqueous (water- based) products restore the lost moisture of finished leather and maintain its natural flexibility. When moisture is replaced the fibres will become flexible again and gives the leather a softer feel. Being in an enclosed space with little to no ventilation will exacerbate dehydration if the leather is subjected to very high temperatures and low humidity conditions the fat liquor oils introduced during the re-tanning process may become destabilised, leading to the finished leather becoming dehydrated.
Apply an aqueous (water- based) product (Leather Master Soft Touch (ex Vital) this is not a conditioner per se but it will revitalise leather that has become dehydrated. It is also excellent for improving the tactile feel of leathers. Apply to surface and allowing it to remain, renewing as necessary. And then apply an aqueous (water- based) protection
