Leather Tanning

While in China I had the opportunity to check out a leather tannery that produces cow and kangaroo finished products for many top brands' performance and lifestyle footwear.

This particulary tannery doesnt process the raw hides, but rather recieves them in "wet blue" form from local manufacturers or imports skins from Australia/New Zealand (kangaroo leather) or Europe (cow leather).

Click the Read More link below for more pics and info about the leather tanning process.






A "wet blue" is a semi processes skin, that is indeed, both wet and blue. The wet blue skin is a result of a chrome tanning process that is done after raw hide is fleshed and the meat and hair is removed and is designed to keep the skins soft and ready for further processing and free from bacterial growth.





Once the wet blue skins are recieved, they are first soaked in water to soften the skin. Then they go through a process called "semming" (not sure about the spelling of this, anyone have the correct term?), which pushes the water out of the skin, but keeps it soft to work with.

Skins are then "shaved" using a special machine that has a fine sandpaper like roller, which makes the skin (especially the bottom surface) more smooth and even.





After this, the skins are split to the correct thickness by being put through a machine that has knife edge which can accurately split the skin in crosssection.







Skins are then graded and measured. Measurement of processed skins is done using a special table that hasa computer controlled laser system which can determine the square footage of the particular skin and add the quantity to inventory.





After the wet blue process, the skins can then be drum dyed, to set a color or finish. The drum dying process involves putting the skins in giant drums along with various chemicals and dyes. A typical skin may go through 4-5 different 40 mintue cycles of dying with different chemicals for a 6 hour total process. Some special finishes can take up to 12 hours of drum dying.



Skins are then air dried for 2-3 days depending of the temperature and humidity inside the factory and can take up to 1 week in particularily cold or wet weather. the the above and below photos you can see the skins hanging from the ceiling on a conveyor system to dry.





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4 Comments:

Anonymous cris said...

Nice articel Richard, interesting insights.
Btw the sneaker fair did not take place and is postponed till september. Don't know why ... Anyway, enjoy and take care

PZ

12:15 PM  
Anonymous J Antonic said...

You should check out the Horween Tannery in Chicago Illinois. One of the last, if not THE last tannery producing genuine shell cordovan. Allen-Edmonds, Alden, Ralph Lauren, Church's English Shoes all use these fantastic hides.

j.
www.unthinkit.com/unthink3d.htm

2:58 PM  
Anonymous Anonymous said...

Good job Richard, I am consumed by this site. The articles are fantastic and incredibly well informed.

Do you know of any other resources that focus upon the football industry, product and branding?

Simon

6:46 AM  
Anonymous Darryl Cassingham said...

Richard,

A few mistakes/errors in your tanning write up, which I must clarify:

1. Wet blue is indeed an intermediatry stage for shipping/transporting various skins/hides to other geographic locations. But wet blue does not make it automatically resistant to bacteria, fungal growth or microorganisms. That is achieved by bacteriostats and fungicides.

2. The stage of 'wetting back' is to rehydrate the skin and provide a consistent base from which to start processing again, due to drying out during transportation. It is not to soften the skin.

3. Samming (the correct spelling) is to remove excess water from the skin ready for a wet shaving operation. More modern tanneries, such as Packer Leather, use automated systems that grade the skins and ameasure area and thickness at this stage for better product consistency.

4. Shaving machines actually use a sharp bladed helical roller system to reduce the thickness of the skin and to give consistency in the thickness across the whole skin. Sandapaper systems are called buffing machines, and can only be used on dry skins, else the paper would get clogged up ;-)There are many other types of machines that can reduce the thickness, e.g. splitting, etc. More modern tanneries split cow hides to gain an additional piece of leather that can be sold for other uses. But on kangaroo there is little option for this, and they are commonly only shaved to a specific thickness.

5. Area measurement is not commonly done by laser!!!! It is simply a photocell system..... lasers are too complicated an inaccurate on this substrate at this stage.

6. Drum dyeing terminology is inaccurate. It is called the retan process, where the skin undergoes a number of pH and temperature variations in different 'floats' of water to penetrate and fix various chemicals, including dyes, retannages, fat liquors and hydrophobic systems.

7. Hang drying is old technology!!!! Most modern tanneries use vacuum dry systems (which don't suck water out of the skin, they reduce the pressure in the drier which reduces the boiling point of water) but these systems also give very good area yield for the tanner.


Obviously this is a very old and low tech tannery you are visiting Richard!!!!! And there are many, many more steps to making high quality and technically advanced leathers. I'd say this tannery is about 40 years behind the times in truth. which is rather worrying I would think from a consumers perspective. Interestingly from the photos it is clearly evident that it is not very environmentally compliant ;-)

Rgds,

Darryl
Technical Director - Packer Leather

8:46 PM  

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