Re: MtMan-List: period tanning / Alans comments

["Matt Richards" <backcountry@braintan.com>]

Johns reply to my comment of not knowing of any other period tanning methods
besides bark, brain, oil and alum was:

Except for oil tanning, egg tanning, urine tanning, buttermilk tanning, sour
>milk tanning, arsenic tanning and acid tanning.
>

I guess a lot has to do with how we define our terms. The term 'brain
tanning' did not exist to my knowledge before modern times. The accepted way
(among the leather industry) of defining tanning terms is based on how the
actual chemical change is affected on the leather. If something actually
changes the collagen proteins of the skin, permanently, it is a 'tanning'
agent.

I am well aware that there was an incredibly wide variety of substances used
and substituted in various tanning recipes throughout the ancient
world....but often it is still considered the same method of tanning. From
the example above 'sour milk tanning, buttermilk tanning, and egg tanning'
are generally considered the same thing as 'brain tanning' as they affect
the leather in the same way. Soap tanning does too. Oil tanning is a
different process because the fish oils (usually cod) oxidize extremely
easily, and in this oxidation they create polymers which change the collagen
fibers of the skin. You can not wash out the effects of true 'oil tans'
There is actually reasonable speculation that this type of tanning was being
done by many native tribes in the northwest, and was clearly done by
Europeans of this era on many of the deerskins that were exported to that
continent. Oil tanning is a term that is commonly thrown around by people
any time an oil is added to the tanning mix, not really knowing what it
means.

As far as urine tanning goes, I'd love to see some evidence of this. I've
met one man so far, who claims to have actually seen someone 'urine tan' and
he has described it to me in detail....so I'm gonna try it. But for the most
part, it seems to be a term that is thrown around, with little real basis.
Urine was commonly used by NW Coast and Arctic people to strip the oils out
of skins that were otherwise just too dang oily to do anything with, but not
as a 'tanning' agent.

And while there were many, many sources of tannins for bark tanning, its
still just considered bark tanning. The hides you are referring too that
were sent from San Franciso to Boston, were destined for bark tanneries (and
soon a huge bark tanning industry developed in California based on Tan Oak).

Lime and saltpeter were both used in many traditional tanning methods, but
neither is a 'tanning' agent, and wouldn't be known as 'lime tan' or
anything like that. Lime was used in the first recorded account of Comanche
brain tanning, and is standard in chrome tanning and bark tanning.

As far as arsenic and acid (besides tannic) tans go, these are modern
methods as far as I know. Do you know of any references to these being done
during or before the period we are talking about?


You asked what I thought of the comments about brain tanning being a
dressing rather than a true tanning.....

I do not know what the accepted definition of tanning was back in the early
1800's, but in modern times, 'tanning' occurs when the protein fibers
(collagen) are permanently changed in their composition, so that the skin
can never go back to rawhide. Brains do not do this, unless they do a very,
very, weak oil tan (by oxidizing).....and I think it is more accurate to
call it a dressing (experimenting with, I have successfully completely
removed all of the effects of the braining by putting a brained and softened
hide in a running creek for three days....all of the tactilely discernable
effects of the brains were gone, it was rawhide again)....however smoke does
tan a hide.

Smoke contains a gaseous form of formaldehyde which is why it preserves
stuff (and one reason that it is carcinogenic). It causes the collagen
proteins to form new links to one another at different points on the protein
chain (this is all in leather chemistry books if anyone is real interested I
could give you some good titles). In graphic terms, it causes the fibers to
form little bridges between one another that are permanent. You can not wash
out the effects of the smoke....the color will wash out, but not the
'tanning'. It'd be more accurate if we all referred to it as 'smoke tanning'
and 'brain dressing' like some folks do....but the term 'brain tanning' is
popular and here to stay.

As a side note, 'Alum Tanning' is not generally accepted as a 'true' tanning
method, because the affects can be easily washed out. That is one reason it
is generally referred to as 'Tawing' rather than tanning.

A great book on ancient tanning methods and recipes from throughout the
world, with excellent yet understandable explanations of the chemistry and
related processes is 'Ancient Skins, Parchments, and Leathers' by Ronald
Reed. It also talks about the conversion of parchments to leathers that you
were referring too.

Matt Richards
www.braintan.com