Leather Quality and Properties

[glenjay]



...
I guess I am wondering if all of the loyal followers of his "method" over in the Alden Thread are going to be in for a rude awakening when their shoes end up cracking much earlier than expected, because they wear their shoes far more frequently (and probably expose them to more weather) than Mac does.  Do you think that shell really has enough oils stuffed into it to survive constant use for many years with no product being added back into it?  You may have already answered this above when you mentioned that you would put neutral cream polish on it, but I thought I'd ask for some details anyway.  Thoughts?

Well there is quite a bit of difference between cow leather and shell cordovan, and therefore reasons to treat them differently.

First, shell is actually produced from a part of the subcutaneous muscle layer in horses called the panniculus carnosus. Because it is a muscle and not a skin there is no grain side and no skin side, it is simply a thin fibrous muscle.

This is one of the reasons that it is hot stuffed rather than fat liquored. Hot stuffing also allows the tannery to add a lot more fats and waxes than fat liquoring.

Beside the additional fats and waxes, another aspect plays an even bigger role: The difference between skin and muscle.

Both skin and muscle are made up of protein filament bundles (fibrils), but they are made up of different proteins. Skin is mainly collagen and keratin proteins, while muscle is mostly actin and myosin proteins. The difference is that the muscle filaments are much smaller that the skin filaments. A collagen protein filament is about 80nm in diameter, while an actin protein filament is about 8nm in diameter (a factor of 10 times smaller). This is why cordovan shell looks so smooth.

Because the fibrils are so much more compressed (ten filaments for every one of cow hide) it tends to retain oil and wax much better.

This compressed fibrous tissue has no real grain side, and so it acts like flesh out leather, similar to waxed leather, but with a much more compressed surface. This is also why a deer bone can smooth out a scuff.

With all that being said, all oil oxidizes over time, so never adding oil to cordovan shell seems a little short sighted to me. I would put a cream coat on every once in a while, just for that reason.

 

[OzzyJones]



I guess I didn't know it was true. But, those brands don't really exist as options to me, so meh.

Meh? Meh you say?! Well to you sir I say pfft!

 

[MoneyWellSpent]

Well there is quite a bit of difference between cow leather and shell cordovan, and therefore reasons to treat them differently.

First, shell is actually produced from a part of the subcutaneous muscle layer in horses called the panniculus carnosus. Because it is a muscle and not a skin there is no grain side and no skin side, it is simply a thin fibrous muscle.

This is one of the reasons that it is hot stuffed rather than fat liquored. Hot stuffing also allows the tannery to add a lot more fats and waxes than fat liquoring.

Beside the additional fats and waxes, another aspect plays an even bigger role: The difference between skin and muscle.

Both skin and muscle are made up of protein filament bundles (fibrils), but they are made up of different proteins. Skin is mainly collagen and keratin proteins, while muscle is mostly actin and myosin proteins. The difference is that the muscle filaments are much smaller that the skin filaments. A collagen protein filament is about 80nm in diameter, while an actin protein filament is about 8nm in diameter (a factor of 10 times smaller). This is why cordovan shell looks so smooth.

Because the fibrils are so much more compressed (ten filaments for every one of cow hide) it tends to retain oil and wax much better.

This compressed fibrous tissue has no real grain side, and so it acts like flesh out leather, similar to waxed leather, but with a much more compressed surface. This is also why a deer bone can smooth out a scuff.

With all that being said, all oil oxidizes over time, so never adding oil to cordovan shell seems a little short sighted to me. I would put a cream coat on every once in a while, just for that reason.

That has been my conclusion as well. Thanks for the thoughts!

 

[patrickBOOTH]

Going back full circle, why do we hate silicones again? People say they choke out the leather or something? Wouldn't silicones actually be better than oils because they don't oxidize? If they do, probably takes like 500 years, right? Speaking of which, what actually IS oxidation? Isn't it just the chain gaining Oxygen molecules over time? So if this is happening and for some reason it is "bad". Shouldn't you have to remove whatever "oxidized" molecules are already on the leather to restore new ones? So this puts it into the same situation as a silicone, which may not, or very slowly oxidize. How does the size of the silicone molecule compare to a plant and animal oil as far as penetration goes?

 

[DWFII]



Going back full circle, why do we hate silicones again? People say they choke out the leather or something? Wouldn't silicones actually be better than oils because they don't oxidize? If they do, probably takes like 500 years, right? Speaking of which, what actually IS oxidation? Isn't it just the chain gaining Oxygen molecules over time? So if this is happening and for some reason it is "bad". Shouldn't you have to remove whatever "oxidized" molecules are already on the leather to restore new ones? So this puts it into the same situation as a silicone, which may not, or very slowly oxidize. How does the size of the silicone molecule compare to a plant and animal oil as far as penetration goes?

I'm not the best person to answer this...I'm not a chemist.

But I dislike silicones because they:

a) aren't a natural product appropriate for leather...If it is not nurturing the leather or enhancing it in any measurable way, why use it? I believe silicones are a by-product of the petro-chemical industry, no direct knowledge in that regard, however;

b)will destroy the ability of the leather to be polished over time;

c) perhaps because of the fact that they don't oxidize, they tend to smother leather and prevent it from breathing. That's why silicones are considered a good waterproofing, by some people. I suspect it's also why NASA won't allow in anywhere near any of its facilities--common wisdom has it that one drop will spread to a mono-molecular coating on every surface it comes into contact with.

I have silicone in my shop. I use it very judiciously to counter the effect of neoprene cement on steel needles. I used to put it on worn outsoles to waterproof them. In my experience it softened the leather, loosened the structure of the fiber mat and made it wear more quickly.

--

 

[patrickBOOTH]

Valid points! Thanks.

 

[Nick V.]

Id like to add that silicone is an oil based product. In addition to clogging the pores of the leather it attracts dirt like a magnet.
The only time I suggest using anything w/a silicone base is when there are no cosmetic concerns. For example, hunting boots.

 

[blazingazn]

Does the thickness / weight (oz.) of leather dictate the quality or durability of a shoe? Like the thicker the better? Or...?

 

[DWFII]



Does the thickness / weight (oz.) of leather dictate the quality or durability of a shoe? Like the thicker the better? Or...?

Durability? Maybe, probably.

Quality? No relationship whatsoever.

Wearability and comfort? certainly.

 

[patrickBOOTH]



Does the thickness / weight (oz.) of leather dictate the quality or durability of a shoe? Like the thicker the better? Or...?

If you look back in this thread it was discussed at great length. FWIW, thickness and weight aren't perfectly correlated. Also, it seems from the discussion that the length and density of fibers is more important in longevity than thickness.

 

[VegTan]



Going back full circle, why do we hate silicones again? People say they choke out the leather or something? Wouldn't silicones actually be better than oils because they don't oxidize? If they do, probably takes like 500 years, right? Speaking of which, what actually IS oxidation? Isn't it just the chain gaining Oxygen molecules over time?

If silicones and petroleum distillates are pure, they never oxidize, but they actually contain impurities. "Dark petrolatum" seems to contain plenty of impurities.
http://digital.library.unt.edu/ark:/67531/metadc6294/m1/17/

I don't know the time scale, but it might be on the order of 10 years, not 100 (10^2) years.


There are three kinds of ***** acids: saturated ***** acids (SFA) which have no double bond (C=C), monounsaturated ***** acids (MUFA) which have one double bond, and polyunsaturated ***** acids (PUFA) which have two or more double bonds. For example, stearic acid is SFA, oleic acid is MUFA, and linoleic acid and linolenic acid are PUFA.
http://en.wikipedia.org/wiki/Fatty_acid

Fats and oils consist of these three ***** acids. For example,

http://en.wikipedia.org/wiki/Coconut_oil
Coconut oil : 91% of SFA, 6% of MUFA, and 3% of PUFA
Olive oil : 14% of SFA, 72% of MUFA, and 14% of PUFA

http://en.wikipedia.org/wiki/Shea_butter
Shea butter : 22-59% of SFA, 40-60% of MUFA, and 3-11% of PUFA

http://en.wikipedia.org/wiki/Tallow
Beef Tallow : 43% of SFA, 50% of MUFA, and 4% of PUFA

The more SFA fats and oils contain, the harder they become, because SFA (above) can become denser than MUFA and PUFA (below).

CH2 next to a double bond is called an active methylene group, while CH2 is called a methylene group. A methylene group is stable, but an active methylene group is considered to be susceptible to ultraviolet and/or heat. (Why "is considered"? I guess it is difficult to verify it experimentally.) Here is a reference: http://books.google.com/books?id=Hcl0fkcrfbEC&pg=PA856&hl=en


　－CH2－CH＝CH－CH2－

turns into a free radical (below) by ultraviolet and/or heat.

　－CH*－CH＝CH－CH2－

* denotes a free radical, which is unstable and reacts rapidly with oxygen to yield a new free radical.

　－CH*－CH＝CH－CH2－ + 02 → －CHOO*－CH＝CH－CH2－ (#reaction)

This new free radical reacts rapidly with unsaturated ***** acid to yield hydroperoxide "#A" and a new radical "#B".

　－CHOO*－CH＝CH－CH2－ + －CH2－CH＝CH－CH2－ → －CHOOH－CH＝CH－CH2－ (#A) + －CH*－CH＝CH－CH2－ (#B)

This new free radical "#B" goes back to "#reaction", which is called a chain reaction (autoxidation). Hydroperoxide "#A" is decomposed into aldehydes, ketones, alcohols, and polymeric compounds. Aldehydes, ketones, and alcohols are causes of bad smell and change in color. Polymeric compounds are a cause of increase of viscosity.

Shunji Kato, emeritus professor of physical chemistry at Osaka university, says the following in his book.

Oxidation rates

linolenic acid : linoleic acid : oleic acid : stearic acid
= 3 double bonds : 2 double bonds : 1 double bond : no double bond
= 100 : 60 : 6 : 0.6

 

[cbfn]

 

[glenjay]



If silicones and petroleum distillates are pure, they never oxidize, but they actually contain impurities. "Dark petrolatum" seems to contain plenty of impurities.
http://digital.library.unt.edu/ark:/67531/metadc6294/m1/17/
...

Silicone and petroleum distillates really have no similarity when it comes to oxidation.

Silicone is a synthetic material (in solid to liquid form) that uses silicon as a bonding agent to carbon, hydrogen, oxygen, and in some cases other elements. It has similar properties to rubber, and is extremely resistive to oxidation (either through oxygen gain or hydrogen loss). And, I suspect the purity is controlled through the manufacturing process.

Dehydrogenation of petroleum distillates by various types of radiation (most typically UV, but gamma and other types of radiation can cause it also) has no dependency on impurities, and is an issue the petroleum industry deals with all the time.

I would avoid putting either in leather shoes because of the moisture barrier they create, but silicone even more so, because it is an even greater moisture barrier and almost impossible to get back out of the leather. Silicone does not really break down over time like mineral oil will, but that isn't always a good thing.

 

[VegTan]



So if this is happening and for some reason it is "bad". Shouldn't you have to remove whatever "oxidized" molecules are already on the leather to restore new ones? So this puts it into the same situation as a silicone, which may not, or very slowly oxidize. How does the size of the silicone molecule compare to a plant and animal oil as far as penetration goes?

I guess nobody do an experiment on oxidation quantitatively over a few decades, so it would be difficult and arguable to answer about that.

Generally speaking, a dictionary by JLIA (Japan leather and Leather goods Industries Association) says:

http://dictionary.jlia.or.jp/detail.php?id=507

Grain cracking happens when leather is bended, pulled, and compressed. It is caused
1) by excessive tanning agents,
2) by denaturation of proteins by ultraviolet, acid, alkali, and heat,
3) by oxidation of fatliquoring agents.

Mr. Giles, Iron Heart UK, did a notable experiment on oxidation over 1.5 years and on a bending test. He used Mustang Paste (horse oil-based paste), Obenauf's Heavy Duty LP (plant oil-based paste), Obenauf's Leather Oil (plant oil-based liquid), and olive oil.
http://www.ironheart.co.uk/forum/index.php?topic=1977.0

As for a silicone oil, JLIA says it is not a fatliquoring agent, but a waterproofing agent. Aquaseal also says:

http://www.aquaseal.com/faq.html

Q. What is the active waterproofing agent of Aquaseal?
A. High density silicone oil.

Q. How is Aquaseal different from all the other silicone footwear care products on the market?
A. Most silicone products rely 100% on silicone for the care and nurturing of leather. While silicone is an effective waterproofing agent it is not a particularly good leather conditioner. Aquaseal, on the other hand, effectively combines silicone with an highly effective leather conditioning agent, which renders a true all-in-one product. Not only do your feet stay dry, but your leather will stay in tip top condition if used regularly.

BTW, here is a brief introduction to silicone tanned leather by Dow Corning.

http://pubs.acs.org/doi/abs/10.1021/cen-v033n011.p1132

SEVERAL FOOTWEAR MANUFACTURERS will have shoes on the market this spring made of leather which is permanently water resistant and which excludes water under flexing conditions. This new concept in leather is the result of a Dow Corning silicone product, Sylflex, which is tanned-in to make shoe upper leather exclude water, stay soft and flexible, and yet breathe.

Charles. A. Eaton, golf shoe manufacturer, and Endicott Johnson will offer shoes made of Sylflex. Almost simultaneously with this, Montgomery Ward will introduce a work and sportsman's boot made from Sylflex leather produced by Endicott Johnson.

Sylflex is the result of years of research by Dow Corning. W. T. Rossiter, manager of Sylflex sales, says Sylflex "has much the same effect on leather as another new silicone product called Sylmer has on upholstery fabric or the earlier Dow Corning Silicone finishes have on apparel fabric." Although there are so-called waterproof leathers on the market today and good ...

http://books.google.com/books?id=70cEAAAAMBAJ&pg=PA138&hl=en#v=twopage&q&f=false

Dehydrogenation of petroleum distillates by various types of radiation (most typically UV, but gamma and other types of radiation can cause it also) has no dependency on impurities, and is an issue the petroleum industry deals with all the time.

I learned alcohol oxidation (http://en.wikipedia.org/wiki/Alcohol_oxidation , http://en.wikipedia.org/wiki/Dehydrogenation) as an example of a dehydrogenation reaction, and I read some books and dictionaries, but they didn't refer to dehydrogenation of petroleum distillates. I thought a dehydrogenation reaction needs a chemical plant/laboratory. Could you tell me the book/paper which refers to dehydrogenation of petroleum distillates?

 

[VegTan]

If silicones and petroleum distillates are pure, they never oxidize, but they actually contain impurities. "Dark petrolatum" seems to contain plenty of impurities.
http://digital.library.unt.edu/ark:/67531/metadc6294/m1/17/
...

Silicone and petroleum distillates really have no similarity when it comes to oxidation.

Silicone is a synthetic material (in solid to liquid form) that uses silicon as a bonding agent to carbon, hydrogen, oxygen, and in some cases other elements. It has similar properties to rubber, and is extremely resistive to oxidation (either through oxygen gain or hydrogen loss). And, I suspect the purity is controlled through the manufacturing process.

I think so, too. Unopened silicone oils contain little or no impurity, but our hands would put impurities in it.

I would avoid putting either in leather shoes because of the moisture barrier they create, but silicone even more so, because it is an even greater moisture barrier and almost impossible to get back out of the leather. Silicone does not really break down over time like mineral oil will, but that isn't always a good thing.

Permeability coefficient is defined by Diffusion coefficient times Solubility coefficient (P=DS), which is derived from Fick's laws of diffusion. Permeability coefficient (or flux) can be measured by experiment.

Here is "Oxygen Permeability through Silicone Liquid Membranes" (I am sorry, in Japanese). This paper says the lower molecular mass or viscosity silicone oils have, the higher permeability they do.
http://repository.dl.itc.u-tokyo.ac.jp/dspace/bitstream/2261/38871/1/sk035006005.pdf

Dow Corning says water vapor permeability of silicones (PDMS) used in cosmetics are 3,737 or 2,578 [g/m²/24hrs], that of mineral oil 2,352 [g/m²/24hrs], and that of petrolatum 31.2 [g/m²/24hrs].
http://www.dowcorning.com/content/discover/discoverchem/si-industrial-apps.aspx

Kanagy and Vickers say that of chrome-tanned calfskin is 2,880 [g/m²/24hrs], that of vegetable-tanned calfskin 2,131 [g/m²/24hrs], that of chrome-retanned upper 1,786 [g/m²/24hrs], that of vegetable-tanned sheepskin 4,368 [g/m²/24hrs], and etc.
http://archive.org/details/jresv44n4p347

BTW, Sierra Trading Post says that of Gore-Tex is 15,000－25,000 [g/m²/24hrs].
http://www.sierratradingpost.com/lp2/waterproof-guide/

As for washing away a silicone oil, if it is a "water-based silicone", it may be washed away easily, though I don't need/use it.
https://www.obenaufs.com/index.php?route=product/product&path=17&product_id=53