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kallenwe
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Posted: 19 March 2007 at 4:58am | IP Logged Quote kallenwe

Thought for an instant there you were going to delve into the tricks that make rawhide white (or transparent, as the case may be).

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DavidR
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Posted: 19 March 2007 at 7:39am | IP Logged Quote DavidR

The inquiry is to how to make inexpensive and uncomplicated white leather, an not white (or even transparent) hide!

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kallenwe
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Posted: 19 March 2007 at 8:59am | IP Logged Quote kallenwe

Certainly was!  Then again the obvious relationship would pull one into the other, especially once you start discussing the role of salt in either.

Then again, there are those who would argue that alum tanned "leather" really is nothing but a glorified rawhide, that the alum is nothing but aluminum salt, certainly not a tanning agent.  Oh, there we are at salt and white again. 

With a little reading between the lines here we can see that white leather is just pure rawhide with no discoloring tanning agents, ie brown tannins or blue chrome.  It is only when we start needing to cover the color of the tanning agent that any other color of leather becomes an issue.  In short, the natural color of "leather" is white.



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mexgerber
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Posted: 19 March 2007 at 11:06am | IP Logged Quote mexgerber

But it is not clear if he can not use just Basyntan or any other synthetic phenolic tanning agent. Formaldehyde is forbidden and is being proposed. Phosphonium salts and oxozolidines may also release formaldehyde, but in lower percentages.
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kallenwe
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Posted: 19 March 2007 at 2:50pm | IP Logged Quote kallenwe

Many of the taxidermists have been doing that trick for years.  It is hardly the most stable tannage in the world, but if the leather exposure is minimal, it should hold up for many years.  Actually it would be interesting to put the phenolic syntan on first and let in penetrate good, then hit with alum to crosslink the phenols.  Out to be a great tannage.  Might turn a bit brown as the phenols link into large molecules similar to tannins. 

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DavidR
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Posted: 19 March 2007 at 5:00pm | IP Logged Quote DavidR

The agreed upon definition (hence arbirary!) for differentiating between hide from leather is based on what one can consider a substantial increase of HYDROTHERMAL shrinkage temperaure upon tannage!  It is just a difficoult to define as many trade technological (not scietific!) concepts. It is like pornography, ard to define, but one seems to know when one sees it!  The smallest increment acceptable over the 50-55 degC agreed value for raw mamal origin collagen I, seemsto be only about 25-30degC as in some weak vegetable tannins.  Yet sulphate washing of chrome chloride tanned leather can raise the hydrothermal shrinkage temperature from about 80degC to boilfroof.  Hence sulphate tannage as part of a combination tannage )chrome-sulphate is considered a tannage whereas raw collagen stabilized in a glaubber salt bath to yield a shrinkage temperature of about 70-75C is still considered raw whereas a vegetable tanned leather with a comparable hyrothermal shrinkage value would be considered as tanned!  I agree then that just like pornography, there are criteria that may appear arbitrary to some, but tanners can more or less come to a usefull consensus as to what tannage is.  I will not call white "leather", Aluminum Sulphate impregnated hide!  Aluminum tanned leather must have polymeric oxolalated and/ or olated long-chained polynuclerar aluminum complexes associated through collagen carboxys with polymeric water "sheaths" surrounding protocollagen structures.  My current and/or protracted ignorance of these details, and how they apply, do not make this so named leather invalid as such!

To propose a combined aluminum mimosa analogy tannage, which could well be boilproof, does not make aluminum tannage as a concept invalid in any way!



Edited by DavidR on 19 March 2007 at 5:05pm


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kallenwe
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Posted: 20 March 2007 at 7:05am | IP Logged Quote kallenwe

Great!  Now we propose theoretical constructs in Alum "tanned" leather that are impossible to quantify and purely the artifacts of over active imagination directly stolen from chrome theory, and I emphasize theory.   Oxolation and Olation with aluminum?  Sure, show me!  And if such wonderful "polymerization" were occurring, then why not similar shrink temps. to chrome?? 

Even in chrome theory these concepts are derived from visible phenomena experienced in chrome solutions, not inside the hide where they are "believed" to also occur because of what is seen in the solution.  No such phenomena are ever noted for aluminum salt solutions. 

No way!



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zercas
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Posted: 20 March 2007 at 12:48pm | IP Logged Quote zercas

I have to agree with Waldo, even though Aluminum forms polynuclear complexes, it does not tan as Chromium, the reason be that Chromium forms covalent links and Aluminium ionic, which makes it less stable; the first has better afinity to COOH groups while the second has it OH groups, there also the diffence of both metals in the combination tannage with Mimosa.    The key word, as Waldo said, is that we " believe " that reactions happen inside from the info we get outside the leather and some times is not that accuratelly.

Regards

Zercas



Edited by zercas on 20 March 2007 at 12:49pm
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DavidR
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Posted: 20 March 2007 at 10:19pm | IP Logged Quote DavidR

I have never said aluminum tannage is functionally or chemically identical to  chromium tannage. As a matter of fact, I guarantee a sure dissaster in using aluminum identically as chrome is, and as was pointed out to you, Zercas, in the paper that I suggested to you as relevant to the nature of aluminum tannage, as it hints to about the real aluminum tanning species, that you considered more of a "laboratory" paper than tannage actual information! You yourself, Zercas, mentioned that you are amazed at Covington's "cross-linking, what crosslinking?" statement denying a covalent tannage mechanism even  for chromium!  A pelt saturated with a soluble chrome salt and never basified, is annalogous, however, to an aluminum sulphate saturated hide that has not been basified and cannot be called "white leather" anymore than the chromium saturated-hide, unbasified,  could be called "green" leather! Neither are leather in any sense!  Some hair-on, just dehydrated, pseudo-leather, are perfectly museum specimen serviceable taxidermy products, but are not leather either!  Many taxidermists do produce white leather, generally in combination tannages, that we do not really know any more than chrome why they really work!  Or do you not think that Covington has accepted with his characteristic unhumbleness not to have the whole picture of tannage yet clear?  If you and Waldo do have it, my hat's off to you!

 Water treatment books, report the existance of highly charged  polymeric species such as Al13(OH)34plus5 and Al7(OH)17plus4 that are involved in ("combination tannages") flock formation with acrylic polyelectrolites similar to acid resin syntans in (now I will use a dirty word according to Zercas and Waldo) colloidal procesess requiring a pH value of a little less than 6, to properly perform.  I don't think it is accidental that Heidemann mentions that a pH over 5.5 is absolutelly required in all the basification of aluminum tannages to avoid migration from the grain through the flesh (lability) without going through the tanning bath!  The many millions of tons of aluminum wet-white historically produced through many years,  where some increased hydrothemal shrinkage temperature is required over that of raw-hide to physically be able to process (shave, etc), are testimony to the real, but more modest, tanning ability of aluminum, that a very durably preserved taxidermist dehydration processing would not be adequate for!  OK, so I believe contrary to most of the establishment, that protocollagen (triple helix) and water polymers form colloidal H-bonded micelles in a thermodynamic CMC (critical micelle concentration) cooperative sense that  are then involved in CAC (critical aggreation concentration) colloidal additional stabilizaton processesing with tanning (co)polymers mainly, and are not generally covalenty crosslinked by either aluminum, chrome or many known  tannins.  This does not mean that aldehydes or others like multifunctional chlorosulphonated parafins cannot form cross linked collagen!  The fact is that we do not yet understand either chrome or aluminum tannages well enough, so it is not very purposefull to comparatively discuss their differences--yet!  My "beliefs", which have evolved in time, have helped me think of ways to solve real tannery problems and ultimately come up with good and unusual leathers, including deer-skin capes for taxidermy mounting purposes, so what I use as my mental models (theory!) for making-up hopefully successfull recipes is ultimatelly between me and my clients, and I thus need no more than results for my purposes!  Nevertheless, as a professional I am willing to discuss my viewpoints not expecting all others to embrace them or even have any interest!



Edited by DavidR on 21 March 2007 at 1:00am


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DavidR
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Posted: 21 March 2007 at 12:27am | IP Logged Quote DavidR

Less than 10% of the fixed chrome may be coördinating to collagen carboxyl groups.  Covington once believed that only 1 in 60 collagen carboxyls actually formed coördinated bonds with chrome!  The truth is, it is just as logical to say chrome polymers H-bond primarily through oxygen bnding with aqueous polymeric water sheaths around collagen! If you wish o call this a supermolecular structure or a colloidal micelle, I do not see too much difference!     The basifiation process helps tan as the removal of the protons from the water sheaths makes them more active towards H-bonding with chrome polymers.  Aluminum will complex with octahedral symetry (six-electron pairs in it's coördination sphere, like chromium!) with oxalate for instance!  Some tanners believe that aluminum thawing becomes full fledged tanning after 3 months rest!  What I am saying is that there is too much uncertainty as how tannning really occurrs, but an increase in Hydrothermal shrinkage temperature is evidence of tannage having occurred, although there is no way to logically annalise comparatively different combination tannages and conclude that the tannages must be linearly additive in contribution to the shrinkage temperature increments.  The uncertainty due to this ignorance is called a synenergistic effect in combination tannage!  Most aluminum tannages as practiced are not properly done in any case from the point of view of pH effects on the penetration and then in the basification as well, because tanners are prejudiced by chromium technology!  The erroneous concept that it is weak aluminum bonding,  the cause of lower shrinkage temperature that Zercas has stated so elocuently, has been disproved by Al27 NMR Spectroscopy that showed the Aluminum bonds surviving aftr the shrinkage process itself!  The reason is because mistakenly considering both chrome and alum tannages as cross-linking, and as Covington says: "What cross-linking?" 

Edited by DavidR on 21 March 2007 at 12:48am


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