Posts tagged #barktanning

The Worst, Common Bark Tanning Mistake

On the road from raw skin to leather, there are many potential mishaps. Skins and plant liquors are potential food for bacteria, yeasts and fungus and growing the wrong ones, or too many, or for too long, can damage or blemish a hide. When dealing with natural materials, we typically have a sizeable degree of variability to contend with. It is very likely that home tanners are dealing with materials and quantities they aren’t familiar with.

One cluster of mistakes that all lead to similar results or scenarios stands out as the worst common error. Put most simply it is, that the hide is left for too long, in solutions that are too weak. This can come about in various ways and have differing effects, but it is super common. In this video, I lay out the typical scenarios and try to offer an approach to prevent them. This is an important video for anyone starting out in bark tanning, because this general area of understanding is so often lacking in the beginning. Nearly everyone seems to make these same mistakes, I know I did, and they need to be headed off intentionally.

Because there are so many variables in natural tanning, it is impossible to accurately quantify all of this. I can’t give out step by step instructions with times and quantities. It just doesn’t work very well that way with all the variables involved, not the least of which is tannin content by species, individual trees and condition of materials. What I can give is a general approach to this problem that will allow you to adapt to new materials and unknowns. That essentially involves observation and understanding the typical way things go as far as the hide tanning rapidly at first, then requiring a high enough level of tannin in the liquor to preserve the skin as it finishes tanning. Also, that some color in the liquor is not necessarily indicative that is has any tanning power left. There is a measuring device called a barkometer, but I don’t own one and find that I can judge when to add tannin by observing the liquor and behavior of the skin. Bullet points are…

*Always look at the liquor, before, after and during, just always; any time you add liquor or check the skin, or have a new batch of liquor. Pick it up in your hand and look at the color and density. All materials are different in color and how much tannin v.s. other coloring matter they contain, so you are making comparisons mostly with fresh, v.s. used and partially used samples of whatever you happen to be working with.

This fresh, strong bark liquor has a bright look and high color density

This fresh, strong bark liquor has a bright look and high color density

This solution, while retaining some color, has no tanning power left, or not enough to matter.  It will grow bacterial scum on top and the hide will decay slowly, because it is just starting to tan.  All color is not indicative of effective tannin.  With a wll prepared skin in new starter solutions, this phenomenon can happen in one day.  Unless you add a lot of tannin quickly, (which is sometimes okay) it will keep happening, but eventually it will slow way down and the solution can be left for long periods of time unattended.

This solution, while retaining some color, has no tanning power left, or not enough to matter. It will grow bacterial scum on top and the hide will decay slowly, because it is just starting to tan. All color is not indicative of effective tannin. With a wll prepared skin in new starter solutions, this phenomenon can happen in one day. Unless you add a lot of tannin quickly, (which is sometimes okay) it will keep happening, but eventually it will slow way down and the solution can be left for long periods of time unattended.

*Understand that in the beginning, hides typically take up tannin very fast.

*If the skin is left for any length of time, the liquor needs to have enough excess tannin to adequately preserve it, and also to insure that tanning continues to progress.

*Be prepared to gather/prepare/add more tanning material as needed. Thoughts such as you used a “lot” or it “should” be enough are not really relevant. It’s either doing the job, or you need more. Sometimes that is a lot if the materials are not very rich in tannin, or it is something that is just hard to gather in enough mass.

*A healthy tan can smell quite strong and in a way unpleasant. I would characterize it as unpleasant, but kind of intriguing and not just flat out disgusting or vile. It is an odd smell that will cling to your skin for a time after touching it. While an element is unpleasant, there should also be a large measure of fermentation to the smell. All of that is normal. It shouldn’t just smell putrid or flat out offensive in the way that rotten food, a dead animal or an outhouse does. Some growth of stuff on the surface can be normal.

*Typically, tanning will progress very rapidly at first, then slow down a lot as the core of the hide slowly tans. Keep the solution rising in strength if anything during this initial phase, then leave it strong enough to maintain a healthy tan as it finishes. Common ways to fail at this objective are: Using low tannin materials, not using enough material, putting the hide in and leaving it without strengthening the tan, Judging by how much it seems like you’ve used instead of by how tanning is progressing (or not), and what the liquor is doing.

*A fairly reliable approach is to cook the material twice. Use the second cook liquor to start the hide, with some water add as necessary to cover the skin well. observe the liquor before putting the hide in. Add the stronger first cook liquor over the several days as you see the liquor depleting and the hide tanning. If you run out and it still seems to be drawing down the liquor, make more. I also talk in the video about dumping some of the liquor to bring the water level down and the tannin level up to get a solution you can leave the skin in. When it is no longer rapidly depleting, you can get the strength up and attend it less frequently. This approach gets most of the tannin out of the material, prevents any possibility of tanning the skin too rapidly in the beginning, is continually adaptable, and encourages familiarity with our materials and their tanning potential.

That is the quicky version, but it should be enough to avoid this worst common problem in bark tanning.

I’ll link two video playlists here. One is a lot of useful general tanning videos and the other is my strops from scratch series, which follows the tanning of a deer skin with oak bark.

Finishing the Oak Bark Tanned Deer Leather

Cute  and  practical, just how I like 'em!

Cute and practical, just how I like 'em!

Last winter I started a project oak bark tanning a deer skin to make leather for the axe strop project.  The project follows the collecting and processing of materials to build pocket sized sharpening strops as prizes for people who completed the Axe Cordwood Challenge.  I'm making everything I need for the strops and decided to show the whole tanning process and everything else in a series of videos.  Almost 6 months ago, I laid the prepared skin away to tan in oak bark.  It sat in there about 4 months longer than it needed to, but I took it out and finished it this week, and it looks like it turned out pretty decent.

The leather is perhaps a little light and spongy, "Empty", as they say in the tanning trade.  Emptiness results from the loss of structural proteins in the skin by chemical or bacterial action.  It isn't much of a surprise considering that I over-limed it to start with, and that it sat in a weak vegetable tanning (plant based) solution for 4 months longer than it needed to.  Those are actually the type of things that a tanner might do on purpose to a hide in order to make the finished leather soft and pliable.  That's not what I was planning though.  I would prefer a rather firm and weighty leather for this project, but that is not even the nature of deer to start with.  Deer skin, at least our deer skin here in the Western U.S. has an open, coarse-fibered, low density character that lends itself well to softened leathers.  It would have been better to move it through the process faster with shorter liming time.  But, a process that uses somewhat preservative solutions like lime and tannin, begs for procrastination.  Add that I have to make videos of it all and it's a perfect storm for not getting things done in a timely manner.  It will probably work fine for the project, but I haven't assessed it closely yet.  If it doesn't work out, I have plenty of other skins I've tanned over the years that are suitable and I got to show the process start to finish, with some of the warts and mistakes that any home tanner is likely to experience.

The next steps will be making the wooden paddles, making glue and putting it all together into the finished product.  I only need a small amount of leather for the project.  Seven brave and industrious individuals chopped one cord or more of firewood for the cordwood challenge using axes only and will receive a finished strop and a leather patch when they are made.  The balance of the leather will be stowed away with the rest of my leather cache, to wait for a suitable project.

The Most Common Bark Tanning Mistakes: Pitfalls to avoid on your way to beautiful leather!

grain header
grain header

By Steven Edholm

Hey!, the Buckeye Gathering barktanning class is coming up and I have bark on the brain.  This article is going to be awesome.  A lot of people ask my advice on barktanning and I see the same mistakes made over and over again.  I can help, because I’ve made them all too (and still sometimes do), so I know whereof I speak!  So listen up fledgling barktanners, because we can save you a lot of frustration, heartbreak and WTF moments.

Procrastination:  This is a common mistake in tanning in general.  I still do it all the time, unfortunately, but I shouldn’t and you shouldn’t either.  Bark tanning is more forgiving than some other types of tanning because some of the solutions the hide is put into can be preservative to a degree, but that shouldn’t be used as an excuse to keep putting off what needs doing.  The solutions used in liming and tanning are not foolproof and will not preserve the skin indefinitely, so try not to use their limited preservative power as an excuse for procrastination.  good luck with that.

procrastination can lead to problems such as this damaged grain, which has lifted from the main body of the skin.
procrastination can lead to problems such as this damaged grain, which has lifted from the main body of the skin.

Using crappy hides:  For some reason, people tend to pick some crappy hide for bark tanning.  I don’t like to start any tanning project with a crappy hide.  It’s too much work to waste on something which can’t be better than the material which you are starting with in the first place.  If crappy hide is all you have and you want to experiment with bark tanning, working with just a small piece of it can be a great learning experience.  And in general, don't be afraid to "round out" scrappy skins, meaning trim off the rough stuff and tag ends, before tanning.  I also don't think it's a great idea to start with a really large hide.  Actually, squirrels are great and make a great starter project, and really nice leather.

This skin is scored.  Try to start with decent skins, or use parts of them to experiment on rather than tanning the whole thing.
This skin is scored. Try to start with decent skins, or use parts of them to experiment on rather than tanning the whole thing.

Leaving in the lime or buck too long:  Leaving the skin in lime or a bucking solution too long is not uncommon.  The skin can stay in for quite some time and come out Ok, but try to leave it in for a reason other than blatant procrastination!  This issue is dependent somewhat on the strength of the solution.  Although long liming is sometimes used intentionally, and sometimes in weak lime, generally you can process the skin as soon as the hair slips out easily.  Overly long liming can weaken the skin and damage the grain.

Failing to de-lime adequately:  Residual lime in the skin can cause brittleness and dark coloration.  Rinse the skin thoroughly many times, and scrape over it on both sides between soakings.  Re-scraping to push out lime and dissolved tissue is called scudding.  You can finish with bating or drenching (soaking in poop or fermenting bran respectively, but that's another story), or at least rinse with a splash of vinegar in water before tanning begins.

Using weak-ass material to make the solution:  It takes quite a bit of tannin to finish out a full skin from a medium sized animal, let alone something large like an elk or cattle skin.  There are tannins everywhere.  They are in most plants to some degree.  Finding sources rich enough, or abundant enough, to make good tanning solutions and finish your project is less common.  Don't use, old dead bark or dead leaves.  You need leaves or bark that have been gathered when fresh, and have not been rained on for a season, or worse.  Keep your eyes out for freshly fallen trees and get the bark when you can, storing it for later.  It is possible to use weak-ass materials, but it is not practical, nor very fun, and the results are likely to be disappointing.  In most cases, older trees have bark that contains more tannins than younger trees.  Stripping saplings may work, but be prepared to do a lot of it!  When you get that good material, chip it up fine.  Boiling large pieces is another common mistake.  You just can't tan an elk skin with some big chunks of old dead pine bark floating in a tub... not gonna happen.

Gather fresh material whenever possible.  Old dry bark that has sat out in the rain is poor in tannins.  Be opportunistic as here where we are gathering bark from a tree that fell across the road.
Gather fresh material whenever possible. Old dry bark that has sat out in the rain is poor in tannins. Be opportunistic as here where we are gathering bark from a tree that fell across the road.

Making the tanning solution too weak:  This problem can happen for numerous reasons, some already covered above.  Many people are so terrified of case hardening, that they start with a very weak solution and then finally end up with a solution that isn’t even strong enough for a good starter.  The skin can be put into a pretty strong tea in the beginning without adverse effects.  It can also be brought up in strength very quickly once the skin is partly tanned.  For instance, you can go from weak to medium over the course of a day and have the skin in a fairly strong solution on day two.  Case hardening is not common and in my experience must require a verystrong solution.  I’m not even entirely sure I’ve even ever seen it at all!  I just threw some squirrel skins into a full strength tanoak tea and they came out soft and beautiful. (full strength meaning shredded tanoak bark just covered with water and boiled for hours, like the picture below.)

This bark liquor is awesome.  It's hard to produce good rich liquor like this from tannin poor materials.  It is possible in some cases, but be prepared to work at it!
This bark liquor is awesome. It's hard to produce good rich liquor like this from tannin poor materials. It is possible in some cases, but be prepared to work at it!

Not strengthening the solution often enough during tanning:  This is the most common mistake.  The skin will use up tannins very quickly in the beginning.  The process slows somewhat until the skin is struck all the way through, but it doesn’t slow down that much unless the skin is thick (think big animals like cattle).  If the tan is agitated, the skin will tan quickly and the solution can be strengthened frequently to keep the process moving along.  The typical beginner scenario is to put the skin in a very weak solution to start with, and then just leave it there until the solution becomes completely used up, which can take only a day, or even just a few hours.  If the solution is not strong enough, the skin will begin to rot.  Add concentrate frequently.  If you are using materials which are poor in tannins, you will need a lot of the stuff to tan a skin (a good reason to do smaller experiments before moving on to full skins).  Don’t judge by how much material you are using, judge by the strength of the solution and how the color is progressing through the skin.  Judging solution strengths is difficult and has to be learned by experience for the specific materials you are using, but I also just don't think it matters that much unless it's too weak, which will be fairly obvious with a little experience.  From what I hear from other people, and judging by my own experience, I’d say that a rule for beginners might be that if you think it’s strong enough, it could probably be a lot stronger.  After the color reaches the center of the skin, most of the tannin binding sites are taken, and the fiber takes up the solution only very slowly.

This is one weak ass tanning solution.  There is basically nothing left in here to tan the skins.  Color does not always mean available tannin.  Add concentrate frequently.
This is one weak ass tanning solution. There is basically nothing left in here to tan the skins. Color does not always mean available tannin. Add concentrate frequently.

Not moving the skin enough:  This mistake is probably most important to avoid during the tanning phase, but it applies to many of the processes, such as rinsing out salt, liming, de-liming and tanning.  Any time a skin is put into a solution, stretch it over and move it around to be sure it is soaked all the way up in all areas.  Several visits may be necessary if the skin is not well soaked up to begin with.  Air bubbles trapped in the skin can also be an issue.   Many beginners stuff skins into a bucket or vat and just leave them.  The skins must have solutions contact all surfaces to be processed evenly.  It’s okay to fold or wad hides into containers, but there should be adequate room, and the skins should be stirred several times a day for the first few days and then occasionally until finished.  If not, they will not tan evenly and can finish uneven in color.  A good strategy for small containers is to remove the skins and put them back folded differently each time.  Just do it often enough.

This skin was dropped in the solution overnight and left there.  Think what would happen if the skin was never moved?  There are exceptions, but generally speaking, more the skin is moved, the more evenly and quickly it will tan.
This skin was dropped in the solution overnight and left there. Think what would happen if the skin was never moved? There are exceptions, but generally speaking, more the skin is moved, the more evenly and quickly it will tan.

Drying the skin without oiling:  This practice usually leads to brittle leather and cracking grain.  It is best to oil or fat-liquor the skin once it is tanned, and before it is dried out.  Otherwise the grain is generally brittle and liable to crack on bending.  Oil functions somewhat like moisture does in living skin, providing lubrication for the fibers and engendering suppleness.

Oiling the skin re-lubricates the fiber and makes for a more wear and bend resistant grain.
Oiling the skin re-lubricates the fiber and makes for a more wear and bend resistant grain.

Bad water:  Water with iron can make skins dark and brittle.  If you have to use high iron water, try to keep the time the skins are in the water to a minimum.   If you have very hard water,or especially if it contains iron, consider collecting rainwater for liming and bark solutions.  It is difficult to collect enough rain water for rinsing processes however.

Whelp, there are of course a lot more details to fill in but, given a basic working knowledge of tanning, that's actually most of the wisdom you need to know to successfully barktan skins!  If you know someone dabbling in barktanning, send them this post.  We rely mostly on word of mouth to get people here.  Please let us hear your experiences and experiments in the comments section.  Hopefully we'll be adding Barktanning to the Paleotechnics class list sometime in the near future!

Posted on April 13, 2013 and filed under Animal Parts, Tanning.