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273974 Brian R <tesla.drummer@g...> 2021‑06‑19 Leather types and contents. WAS:VCI paper/chisel tip protectors
With all the talk about the properties of leather I was reminded of an
article I wrote in April last year:
http://zengrain.com/leatherwork/leather-types-and-terminologies/

Whenever I get confused with terminology and processes I like to take a
deep-dive into the subject and write a cited summary for my future
reference. I'm not an expert (or really a leatherworker) but I based this
on standards, lots of research into manufacturers and reference works on
leather production. If anyone knows of errors please correct me.

The take-away is that almost any leather can be of any pH and contain
chemicals that induce or hinder steel corrosion or even treatments applied
to steel for that purpose. Further, you can't really tell any of this from
looking at a piece of leather on the bench, you'd have to call the tannery.
The original contains citations as well as additional information on grain
and names. I've only quoted the section that discusses chemical treatment
(in vague terms).

"
Leather is not leather. I mean it is *leather* in the sense that it is hide
from an animal prepared for use. After that all bets are off. Did you ever
notice how different wallet, shoe, car seat and jacket leather are?

These differences come from the type of hide and tannery processes. In most
cases the animal that the hide was removed from isn’t the largest factor in
the material’s properties. This is not an authoritative guide but instead
is composed of gleanings.
Basics
This is a summary of the production process so the following leather types
make sense, not a detailed description.

Prep
The hide arrives and the hair is removed and the inside of the flesh is
trimmed to a somewhat reasonable even thickness for handling. The hides are
washed and often stretched. Then the hide is treated with chemicals to help
remove unwanted proteins and oils (liming). Hides are then often bleached
to yield a lighter or more even color. Then the pH (acidity/alkalinity) is
modified for the tanning process (pickling).

Tanning
The leather then goes through the actual tanning process. Most common in
order are chrome, vegetable, aldehyde and alum. Some leathers are
re-tanned, typically with a different form of tanning. This usually takes
place after further processing of the hide, but could be done back-to-back
with the original tanning.

Treatment (crusting)
This encompasses a variety of steps after initial tanning but before
finishing (if finished). Splitting, dying, re-tanning, graining (or grain
correction), filling (for hardness/density), stuffing (with waxes/oils),
conditioning, and softening are some additional steps to prepare a hide.

Finishing
This includes steps to finish the surface and can include physical
processes like flattening and embossing as well as chemicals to coat, seal
and protect the surface of the leather.
"

Brian Rytel
273979 Tim Pendleton <tpendleton@g...> 2021‑06‑20 Re: Leather types and contents. WAS:VCI paper/chisel tip protectors
Thank you for sharing your research.  I had no idea about double tanning or
the differences between many of the leather types.

With your info in mind, I will certainly avoid harness leather when
crafting my next Greek God thong.

Tim
Airing out the LN froe today to split some fresh-ish oak with a neighbor.

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