Caffeine: the most potent artificial intelligence drink!

Caffeine: the most potent artificial intelligence drink!
Deep in the Lair of the Perpetually Curious Fox

Saturday, 29 October 2011

Bark tanning hair on deer hide

So, I noticed there's a salt cured deer hide sitting in the garage loft that's been languishing there for 12 years. I thought, hey, why not try tanning it with whatever I can find on hand? Not being a chemist or a farmer, I do not have any alum (hydrated potassium aluminium sulphate), nor do I have any spare brain to attempt a brain tan, thus bark tanning became the method of choice. 

Where does one find bark? Everywhere! Some bark are better than others due to their high tannin content, but really, you can use any type of bark that leaches tannin into water. You might need a heck of a lot if the bark is poorly tanninated (hahahaa made up word!) or relatively little amount of bark for tannin rich ones. Traditiontally people use Oak or Hemlock bark, and if you google the various taxidermy and paleotech forums, those usually are the bark of choice, but I kinda like doing things in a new way ... so a literature search (thank you google scholar!) on what North American trees have high tannin yield, and are available locally was done. Found many sites, but I will only quote these two just to stop sounding too bloody academic. Here's one that lists different regionally available North American trees with their relative tannin contents in various tissues :
1- Hernes 2004 GCA Tannin signatures.pdf (application/pdf Object) and if you look at the table of sum of tannin in tissue content lists oak, hemlock and lodge pole pine as the highest. Since Pines and Spruce are closely related, on a hunch a searched for tannin content of spruce bark.

Indeed, spruce has lots of tannin in it, but traditionally they were ignored as the bark is pretty thin; it's not viable, amount of work to product-wise, usually, to chop down a spruce for the tannin. Here is the paper on the content of tanning in a particular species of spruce: (paper on Tannin content of Sitka Spruce). BUT if you already have lots of spruce bark available (mulch from garden centres, spring prunings) then there's no reason not to use it!

OK, ingredients are readily available, and I've got time to kill. Lets tan that hide! 

First of all, if you have a freshly skinned hide, you'll need to remove as much of the flesh, fats, connective tissue and membrane from the flesh side as possible. Since I started with a salt cured hide, I hydrated it first in a weak borax bath. When I say weak, I meant 1 cup of powdered borax crystals in about 20 litres of water.

A lot of tanners start by soaking in hydrated lime, ash powder, soda ash and other strong alkali to help ease the fleshing. However, if you're planning a hair on hide, do note that strong alkali is also a strong depilatory agent, thus not really a good idea. That was why I chose borax, which is weakly alkaline. Why the alkaline start? Well, if you remember your basic high school chemistry, base reacts with fats to form ... soap! Saponification of the deer fats in the skin and the tissues by the borate ions does help the fleshing immensely but without the epic hair slippage of strong alkali.

If you want hair off, then go ahead, raise the pH (as I said, soda ash, wood ash, hydrated lime, heck even use NaOH). The skin tissue will also change into a really strange gelatinous, translucent, really soggy, slippery wet mass, though! There's also some mention of the strong base can weaken the collagen in the hide ... but I don't know. Maybe I'll do a quantitative strength test on the next hide which I'll do hair off.

Deer hide in borax bath for 2 days.
I do find that salt curing the hide also helps shrink the membrane from the hide, so not only does it preserve the skins, it also helps when you flesh it, later on when you are not too busy butchering deer. Next comes the fleshing, and since I am just doing things with readily available items at home all I used was a sharp knife (and lots of sharpening!). I can see why some people resort to fleshing using a power washer. I kid you not, it's a LOT of scraping! Since I have moderate RSI I have to stop and rest my hands every hour or so... it took about 15 hours in total of scraping with a knife.

You can see the membrane and some bits of fat still attached, compared to the scraped bit on the bottom right of the photo

Bits of saponified fats, tissue, membrane.
After 15 hours of scraping, stretched leisurely over 3 days, hide is about 99% un-needed bits free. Then it goes through a good rinse, until the water runs clear. For the next step to work, the alkali must be gone. If you're the alkali crazy person who loves to soak hides in strong bases, neutralisation is essential!Some even go ahead as acidifying the hide before the next step.

Nice good wash

I let the hide drip dry (not completely dry, but to the point it's slightly damp) with the flesh side out, so I can inspect for any spots that I missed. So far so good. The scraped hide looks bluish white (which of course doesn't really show on camera)

Clean skin! Notice a few overly deep scrape marks? Well, for a first try on wetscraping I give myself A-
Oooh yeah! Here comes the bark tea! I used garden bark mulch that you can get from garden centres, and with whittled bits of spruce bark from my other projects to make this tea. And yes, it does kind of smell like tea ... sprucey tea. How much did I use? About a kg of bark in 2 litres of water, boiled for 2 hours. Then I pour it into the tub with another about 18 litres of water - just enough to submerge the hide in.

I started with a weak tea first so I don't shock the hide too quickly and avoid case hardening.

After 3 days, I lifted the hide out to re-scrape some stubborn areas and to check for rot. The hide has taken the tannin a bit, it looks a light cream colour instead of bluish white now. Now, with regards to rot, some people put lots of salt (you know, NaCl) into the bark bath, or acidify it with citric or oxalic acid, to discourage bacteria growth. I didn't do either of those, as I'm counting on the bark itself containing lots of sugars and phenolic compounds that would naturally ferment and turn acidid. I did have a quick taste of the bark tea, and yes it is somewhat sour with a puckerish taste (like very strong overly brewed black tea). I deemed it sufficient to inhibit any putrefying bacteria.

3 days in bark tea

The tea also helps you notice more stubborn spots that needs scraping.

Nice colour, right?
Some people might comment that my tea is not strong enough, etc due to the light colour. I have to point out that it's pretty cold here (about 5 to 7 deg C during the day, below freezing at night) and like any good chemical process and reactions, it slows down tremendously when them molecules don't have enough kinetic energy (see, who says a physics degree isn't useful?)

The whole project is surprisingly un-smelly, which contradicts the old adage of tanneries stinks to the high heavens. Mind you I did not bate the hide - google "leather bating" it will give you a hint on why tanneries tend to smell so bad. I made sure to stir the bath, lift the hide and agitate it every which way to make sure the tannin soak is even. All I can smell is ... tea! Even wasps ignored the hide which is a good indication that no flesh smell, or rot has happen. If you start smelling sulphurous smells... then you've got bacteria problem. Make sure the hide is FULLY immersed and there's no trapped air bubbles in the folds.

day 10 in bark tea. Even darker colour now.

Close up
Oh yes, and more scraping too. Personally I don't mind all the scraping. It gives me an excuse to closely inspect every inch (2.5 ish cm LOL) of the hide for any sign of things going wrong.

Bark sticks on everything

Gave the flesh side a quick rinse with the hose before the scrape

Drip dry for a bit

Cut through the neck piece to check if the tannin is soaking through OK. Middle is still a bit white.

Knife, brush (for the hair side), whet stone, and pumice (which I ended up NOT using)

Yes, the hair side is fine ....

Decided to give the hair side a quick brush and clean with some soapy water. Some fatty tissue and membrane got stuck on the hair!

Shampoing a deer is kinda strange ...

Nice clean rinse.
Now to make a stronger batch of tea - I decided to pour out the old tea as there's bits of stuff floating in it, and I just don't want them to re-stick on the hair side again. Spruce bark steeped in hot water over night ... yum ...

Hide is being submerged by the bricks.

Day 17 in the bark tea ... nice chocolate colour now! Nearly done, I would say!

Starting to look like tanned leather.

Hair side still looks good

Even smells sprucey!
After 17 days in the bark tea, the texture of the flesh side changed from wet, soppy, slippery texture to feeling "dry" to the touch. Sounds paradoxical, but if you ask my nerve endings, they say it feels "dry" despite being dripping wet! Such is the astringent nature of tannin!

Bark tea before strengthening.
bark tea after strengthening.
Well, that's as far as I've got so far. I waited this long before putting this article up as I wasn't sure if things are going OK at first. A lot of people say "oh, you should put acid in it!, "oh, you need to check the pH with a meter", "oh, you didn't soak it in lime before tannin, it'll never work" ... so I figure I'd see if my method works before I put this online

Day 25!

Wow, time really flies when you're busy doing projects! Decided to bring the whole operation indoors before it all becomes a deer and spruce flavoured ice cube!

You can see the ice crystals on the hide ...

Looks, feel, and smells like leather now.
I cut a snip from the thickest part of the hide to see if the tannin has reached the centre of the skin - to have a more objective and qualitative comparison, I put it side by side with a snip that I took on day 10.

Day 25 on the left, day 10 on the right. Even the hair has started to take up a bit of tannin colour.

You can see that the middle of the 25th day snip is cream colour instead of white, like the 10th day snip.

Visible even with a dodgy camera focus.
I'm leaving the hide in the bark tea for another two weeks before dressing with oil and working it. Check this space!

OK, today is the 1st of December, about 6 weeks after the initial bark tea soak.

Sorry for the long wait ladies and gents, but I've had the sneezies for a week, then was out of town for 5 days for the last few days of huntin'. Hide has struck through! Yay!

Since the project has been moved to the basement it's a bit harder to hose the hide for rinsing ... so I took a bold (and most probably stupid) move of using the top loader washing machine LOL. 

2 delicates cycles on tepid water with a little bit of mild soap, and final rinse (also tepid delicates cycle). I was expecting clumps of hair to peel off ... but you know, the tannin really worked well in setting the hair into the follicles! Only a small handful came off, and most of them from the areas of the hide that I accidentally over-scraped (exposing the roots. I'm still learning :) ) anyways. I'm not too worried as these are the areas I'm going to trim off after working. I just like the extra hand grips for softening the edges.

So wash with soap cycle 1

Cycle 2 looks pretty much the same. Then rinse

Yes, I did let the hide go through the spin cycle (GASP!) as the whole barrel rotates anyway and no mechanical rubbing to muss up the hair. Due to my hand injuries, I can't lift the hide out of the tub unless most of the water is spinned out.

Now back into the tub to transfer to another warmer room

Bald spot on the overscraped belly skin. Need to be more gentle with bellies next time, notes to self. But hey, the belly skin will make a nice coin pouch :) 

The flesh side looks nice, lighter colour now. Golden brown, texture like sun ...

Hair side looks really nice. Tinged with gold from the bark tea. Even tugged it a few times while lifting, and no clumps came off. Maybe one or two incidental hair, but nothing to fret about :)

I'm letting it air dry with the hair side out until I can get my act to together for a long, comforting, sit down oil and stretch in a few days :) If it dries out completely I'll re-wet it by rolling/folding in a damp towel.

I did take off a hand sized snip from the neck to experiment with a dressing mix ... and I must say I like the result (the bark tanning hand snip is lying on top of another mule deer hair on scrap hide tanned using alcohol/turpentine soak):

The hair side definitely has a golden tinge to it. Lovely!

Am really excited on working it! Can hardly wait! I also like the fact that it smells sprucey

Here's some more pictures of what it looks like as it's drying:

Draped over the backs of two chairs, with the hair side out, to dry.

Almost completely dry; folded lengthwise to show the flesh side

 Close up of the bark tanned flesh side.

1 comment:

  1. this is such a great blog, a friend turned me on to it. thanks for posting! Can I ask, how much spruce bark to water did you use on your second tanning solution?