Posted: 07 January 2010 at 1:11pm | IP Logged

Tanners have used BCS (ordinary tanning chrome salt) as an inexpensive dyeing auxiliary that initially helps to level-out and penetrate the dyestuff because of anionic chrome complexes formed initially as the excess of sulfate ion in the coördination sphere of chromium make anionic complexes that screen-out cationic aminos from picking up the anionic dyestuff, because chrome tanning salt has because of its manufacturing, about a third of its weight in Glaubber's salt. It is sulfate as a Hofmeister anionic protein coagulating (and thus weakly tanning!) ion that "screens-out" or "masks" anionic aminos from reacting.  The formation of chrome anionic complexes by excess sulfate anion is important as well in modern tannage procedures.  If the float is low and relatively cool, the dyestuff anionic colored radicals will agregate colloidially such as detergents do, because of their very anionic sulphonate ends orients the molecules into water micelles, that are destroyed by heat and and low ionic strenght caused dilution, such as detergent-water micelles are.  After the desired dye pentration in a cold, relatively neutral, higher ionic stenght bath in the presence of anionic chrome complexes, then and only then, a very hot, large volume, of acid laden water is added to increase astringency between dye and collagen, dilute the dye-water micelles below their CMC value, and beguin the process of removing anionic sulfates out of the coördination sphere of chrome as less anionic carboxylic funtions in collagen replace them, thus generating tanning enabled cationic chrome complexes that can react with saline links, decoupling them, to further create cationic amino groupings on collagen that are highly reactive to dyestuffs.  This process takes time and higher temperatures, but can yield excellently dyed two step nubouks with out expensive cationic dyeing auxiliaries as well as provide for chrome retannage of the proper crust after effective buffing favored by low chrome contents.  In fact one can have a very low chrome colorless crust, easily dyed in any color to highly brilliant shades because of the cationic chrome retannage in the dyeing process!

Part of the problem in applying this concept is changing the tanner's prejudice of what chemicals need to be used in tannage and which in retannage!  The truth is that there is an administrative, not an absolute chemical reason, for adding certain chemicals in tannage or retannage that shapes our leather processing logic.  True, why add more chemicals to what will become shavings anyway!  But if the shavings are easier to biodegrade, why chrometan to boil-proof if we can later get this property without wasting expensive and effluent problematic chemicals such as chrome?  The wet-white concept really was this but has really failed to be greatly addopted.

Posted: 08 January 2010 at 6:58pm | IP Logged

Most dye suppliers will not wan't to admit on the benefits of sulfate higher ionic strenght initially contributing to the process to cause formation of levelling anionic chrome complexes.  They struggle to remove sulfate from their dye-stuffs and other chemicals!  Also, in the presence of a cationic tanning metal, many dyes become "metallized" to give very different hues from the relativelly simple color prediction diagrams that salesmen use by telling the owner of the tannery that he needs not to have an expert color matcher and any ordinary worker can make the leather the client is requesting with their very scientific looking chromatic diagrams!

Aluminum because of lowered coördinating properties cannot be made to turn cationic after dye penetration such like chrome does.  I recommend using aluminum sulfate dissolved in the final formic acid to fix better all anionics and have cleaner effluents.

Posted: 08 January 2010 at 11:02pm | IP Logged

Dear David,

I used bate in fixing the dyes (Suede), and in fatliquor added o.05% of Glycerin , that will emulsify and remove surface grease of the skin and penetrate smoothly. This I applied when I was in Vaniyambadi.

Posted: 09 January 2010 at 10:12am | IP Logged

Since bate is protein composed, you are most likely to be dyeing the bate! Glycerin is hydroscopic, that is, it picks up water from the atmosphere.  Your idea is widely used in fatliquoring, but using cheaper but simmilar hydroscopic ethylene glycol.  The humidity picked up, increases the sellable area of dry leather and has a natural lubricating effect by dissolving salt-links that hold dry fibers of leather together, making the leather softer.  Glad to see you again on the forum, we always appreciate your practical point of view aqquired from your wide experience.  I miss India's tender coconut water very much living in the Great Chihuahuan dessert!  I cannot even get in in cans anymore!

I miss Vanyambody where I did very interesting beamhouse using bisulfite chemicals in a Musslim-owned tannery that was having problems in their initial soak.  Mr Rafatullah was my collegue when he was associated as a technician with a local agent for Lowenstein (Thiagu), before he started to work for the Italians.  Is Rafatullah's own tannery working or still closed? 

Posted: 10 January 2010 at 7:41am | IP Logged

Dear David,

Now that I compleated my thesis writting for PhD. Topic is well known to you.

"Vedas- A New Critical Analysis with Special reference to human body and health."

In this I am specfically quotes about the supportive therapy to cure cancer and the NaNo application of sending NaNo rays in to the body by splitting them with Copper balls. The heat generated by burning lamps with herbal oils.

According to me/ or nature when the atmosphere is responsible (Smoking) for favouring cancer, why the same atmosphere can not be upgraded so that it can give supportive atmosphere in curing all kinds of diseases.

If my theory is accepted by the scientists and further research is applied our leather industry will travel in path where the pelts will be tanned with herbal tan and dyed with Natural dyes.

I wish to share my findings with our members. Soon I submit and attend viva voce, I will send the entire thesis in PDF to all our members by mail.

Posted: 10 January 2010 at 8:50am | IP Logged

Good for you Rama, congratulations. We will be looking forwad for that thesis. We all wish the best.

Regards

Zercas