Posted: 15 January 2010 at 2:02am | IP Logged

My trick for getting very little break in nappa is placing some aluminum just below the wet-blue's grain, at the junction with the reticular layer.  This is easy to do because aluminum tannins yield huge multinuclear species at slightly higher pH values than about 3.3-3.5  Some of these high molecular aluminum species consist of 13 member structures or higher with difficult penetration status.  The people that understand the flocculation of muddy water by aluminum salts know about these high molecular weight species much better than tanners that are still thinking in terms of  "basic aluminum sulphate" as annalogous to BCS tanning products. These aluminum polynuclear species will react with acid acrilic resin tans similar to Retan 540, or polyelectrolyte resins for treating water!  In fact one of the tests recommended for Retan 540 exhaustion is using aluminum chloride to check for milkyness as evidence of the resin not yet exhausted in the bath.  Since these carboxylic groupings on the resin will coordinate with chrome already in the wet-blue, the use of aluminium at the grain-reticular layer junction causes a sort of "drum impregnation" phenomenon yielding an excellent break without hardenning, especially when a neutral beta naphtalene sulphonic slightly basic syntan is employed to basify the combined chrome-aluminum acrilyc resin retannage.

Floater on the other hand, is enhanced by blocking future fiber adhesion between layers by neutralizing at a higher pH (~7) the cationic aminos in the outer third of the wet blue grain, so the fibers do not stick together via saline bonds when the leather dries.  If an aldehyde is applied on the thin section of both  lyotropically and alkaly osmotic swollen grain layer only, by an agent such as lime, such that the aldehyde astringency towards the neutral amino groups as some dehydrating salt is also applied, it shrinks the swollen grain and breaks-up the sites for interlayer saline bonds to reform, preferably in the presence of an strongly anionic fatliquor.  Careful procedures must be controled for lime penetration should only be just under the swollen grain layer so physical strenght does not suffer excessively.

Thus fibers can be chemically prepared to favor an impecable break as well as a mildly shrunken grain giving rise to a floater type leather.  Does this answer your questions?

As a related side topic let me add that sometimes one can repair slightly loose grain in a leather crust by washing with water with enough formic acid to lower the cut pH to about 3.8-4 and then just gently redry!  The charged aminos formed will cause fibers to stick to ionised carboxyls and tie down the layers again, but slightly harden the leather.

Posted: 15 January 2010 at 9:49am | IP Logged

See David, you are a genious, I always have said that, it is when you out on a limb with your semantics and fancy words that you get in trouble. Why don't you write a book on the real practices of treating leather, it would be fantastic, a best seller.

I really mean it, I know that it is your " modus vivendi" as a consultant but it would be a shame that when the time comes for you and me to go and "push up daisies" all that knowledge will be lost for the ages.

My admiration for that knowledgable response.

Regards

Zercas

Posted: 18 January 2010 at 12:08am | IP Logged

DavidR,

Really appreciate for your nice respond, which inspire me a lot.

Although, my enquiry is about leather mechanics property according to its dimensional structure.

Maybe I should ask a physicist who specialise on material mechanics.

Posted: 18 January 2010 at 9:30am | IP Logged

Look LeO-1, not everybody knows everything. Even though I have some times discussions with my friend David, mostly on workds, he gave you a pettry good answer on how to get to certain states of physical properties.

But if you want to look for more deep answers, just "Google it" , it is all out there.

Be courteous, PLEASE.

http://www.springerlink.com/content/j727h62143788216/

Regards

Zercas

Posted: 18 January 2010 at 9:35am | IP Logged

Here is the "whole enchilada" 

http://www.google.es/search?sourceid=navclient&hl=es& ;ie=UTF-8&rlz=1T4GZEZ_esMX321MX321&q=leather+mechani cal+properties

Zercas

Posted: 19 January 2010 at 7:00pm | IP Logged

Hi Zercas,

Thanks for your help!

Maybe my poor English expression shows uncourteous, if that, I　apologize cordially. As you said, not everyone know everything. So if I can not catch what I want to know, I just say this is not the very answer. But anyway I appreciate David for your answer  inspiring me from another piont of view. 

David,

you are genius and generous !