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Until this (sh*t)storm blows over this will be my last contribution to this thread
Fwiw, this is THE place to have these **** storms. Exactly why SF is so great. Not for the weak and sensitive. No sense if everybody is just going to agree all of the time. So with that, same to you buddy...
Glenjay
Don't take my word for it. Look it up in "Tanning Chemistry, the Science of Leather" by Arthur Covington, now Emeritus Professor of Leather Technology, University of Northhampton. This is considered the standard leather chemistry textbook. In it he says
Well, you cannot "replace oxygen atoms with amino acids". Chemistry does not work that way. Amino acids contain oxygen atoms. Oxygen atoms are much smaller than amino acids, and amino acids would not fit into the locations where oxygen atoms are found in the amino acid chains of collagen- or for that matter, any other protein. To the extent that hydrogen bonds are formed then they would have to be with atoms like oxygen. Since the proteins are made of amino acids, the hydrogen bonds are between hydrogen atoms and oxygen or nitrogen. So, if you "replaced" an oxygen atom with an amino acid, you would have replaced it with a molecule that contained oxygen and nitrogen, and hydrogen bonds would still form. But you could not do this because the protein structure would not permit it.
Yes they are as part of modern leather fat liquoring. This is part of the reason that leather loses little fat during its lifetime. The methods used to fat liquor involve carefully controlled temperature, ionic strength, pH, emulsification, and agitation- chemistry again. The fats then bind to the leather and stay there. You might see "Theory and Practice of Fat Liquoring" and "Fat Liquoring pt1" and "Fat Liquoring pt2" ,all published in World Leather. In times past leather was treated with oils and waxes that did not bind to the fibers, would migrate out, and had to be replaced. This was the work of curriers. That business appears to be about gone, since fat liquoring took over.
Conditioning is done primarily to adjust the moisture content of the leather. In studies of leather properties, the samples are "conditioned" at standardized relative humidity to adjust the water content. Adding oil to replace lost oil may be necessary if the piece has been treated with something that can remove the fat (like the VOC's discussed above). But if you do not do this, then modern leather will lose little of its fat in normal use.
In a related discussion on AAAC, the member calfnkip, who is in the tannery business, had the following comments
“...when the leather arrives at the shoe factory, it is fully fatliquored / conditioned and ready to be made into shoes that are meant to give years if not decades of service.
Under normal use, small amounts of these fatliquors may leach out of the shoe’s leather due to the flexing it’s subjected to when you walk. The quantities that migrate out of the leather this way are pretty small and shouldn’t compromise the integrity of the collagen fibers for some time - - often quite a few years if the tanner has done his job properly. And you are correct that it is not really possible to restore all the fatliquors, greases, waxes and other compounds that are applied to footwear leathers during the tanning process.”
He does not elaborate on why is it not possible to restore the fat liquoring, but the problems are: the fat liquoring is performed with the leather in a drum, heated, with a series of chemicals that are not available to the consumer, under pH and ionic strength conditions that are adjusted for the particular liquor and leather. All sides of the leather are exposed. At the end of this process, some of these conditions are carefully altered to complete the binding, extraction of emulsifiers, or in other ways. These cause permanent changes in the leather, which may not permit more fat liquor to be added.
In response to a question on this topic, Steve Gilbert of the American Leather Chemists Association posted this comment
“...under normal conditions there is not need or in reality no real possibility to re fatliquor a finished leather article. It is part of a chemical process during tannage.”
If you search Science Citation Index, you will find papers describing the uses of humectants in maintaining the water content of finished leather. PEG, sorbitol, and glyercol seem to be the most common.
Until this (sh*t)storm blows over this will be my last contribution to this thread
totally agree with Crat at that point!!Its not the debate that I don't like, its the tone.
FWIW I think this is the perfect place for a debate between knowledgeable people, even if I don't understand the first thing about the chemistry involved. I mean, if not here, where else would such a debate take place? I would like to think that we are all getting a little more knowledge about shoe leather, and that is one of the reasons why I come here. This is SF at its best IMO. If you don't like to read long posts, just scrolll past them, or better yet, post pics of some well shined shoes! This thread can have both.
Agreed 100%
This is the shoe care thread so the discussion was totally in accord with the thread title. And it's a very good development from shoe shine Appreciation...
Its not the debate that I don't like, its the tone.