How to “harden” leather?

i,ve been sucsessful stiffening buckskin by treating it with tung oil. makes it somewht stiff and gives it a nice aged look.

You can try cuir boulli, or "boiled leather." Depending on temperature and soak time it can be anything from kind of resilient to rigid armor. Here's a way to experiment:

Get a candy/cooking thermometer so you can heat a pot of water to about 180F.
Cut five small (2") squares of your leather and poke a needle hole in the center of each.
Thread a string through the center of each, tying a knot under each piece to keep it from sliding, about 3" apart.
On the top piece, write "30" with a sharpie. "60" on the next, "90" on the next, then 120 and 150. That's seconds in the water.

Set up a clock or timer with a second hand or seconds display.
Bring the water to 180 and dunk the whole string of pieces in, holding the end of the string.
At 30 seconds, lift the "30" piece just out, at 60 seconds the "60", and so on.
Let the leather pieces cool and test the resilience of each piece. This will give you an idea of the proper soak time for the stiffness you want.

Important: Cut the squares *exactly* to a dimension so you can measure the shrinkage from the process.

Good luck!

I recently made a sheath for my leatherman to fit in with my m/l stuff. The new oneshave snaps. Ugh. It came out too soft and pliable. And color too light. I dyed it dark brown and left the Leather man in it while it dried. Turned out stiff as a corpse and perfectly formed.

John Spartan said:

Now this is interesting. Guess I always thought of leather like a more complex fabric. It may stain like fabric but oil can be, at least partially, removed and then “toughened” up by the above methods.
Well I am kind of the original “mad scientist” in these matters and not afraid to try some ideas. Keeping in mind there are degrees of everything lets see how right you are!

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No, it's skin. It's not comprised of textile fibers but skin cells. What happens is that those cells absorb more oil than they can hold and burst. When that happens the material loses its structural integrity. That is what makes leather floppy and soft. It's permanent damage that cannot be undone.

Pietro said:

FWIW, John, I've learned to never oil my leather goods - I just apply a renewable light coat of clear shoe polish to protect it from mold/verdigris.

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There's no reason to go to that extreme either. Leather is skin that has been dried and no longer has the mechanisms to replenish the natural moisture it needs to keep it from drying and cracking. It needs oil. It just doesn't need too much of it.

GYJ said:

No, it's skin. It's not comprised of textile fibers but skin cells. What happens is that those cells absorb more oil than they can hold and burst. When that happens the material loses its structural integrity. That is what makes leather floppy and soft. It's permanent damage that cannot be undone.




There's no reason to go to that extreme either. Leather is skin that has been dried and no longer has the mechanisms to replenish the natural moisture it needs to keep it from drying and cracking. It needs oil. It just doesn't need too much of it.

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Well unfortunately that all makes sense. Of course I knew leather was skin but didn’t think about the “bursting cells” part. With that said they’re certainly are synthetic ways to toughen it up I would think. Let the science continue!

Frizen Stalls and Cow's Knee don't need to be hard nor stiff. Water resistant is what matters.
Just make the item and paint it with hot, melted beeswax. The wax will 'stiffen' it and resist water at the same time.

Now, if the leather is Too Thin for the desired project then stiffness wont help. No choice but get different leather or layer the existing.

Also not mentioned yet is the Type of leather; cow, pig, deer, etc
And what cut is it: top grain, suede....if it has been sueded (top and bottom layer cut off) then 'hardening' it will be futile.

More information for the brain bank. Thanks!
As an aside got some beeswax coming this week.

John Spartan said:

More information for the brain bank. Thanks!
As an aside got some beeswax coming this week.

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With the beeswax: dont dip it in, you will get too much and messy.
Best, imo, would be to heat the leather, just a little, I use a standard hairdryer (covers more 'area's then my little heat gun) then with the leather warm just paint the melted wax on and hit it again with the hairdryer (heat gun) and the leather will soak it up - let dry, done.

It is almost always a very bad idea to heat leather. Heat will harden leather, but also leave it brittle and prone to cracking. Nothing that is expected to flex should be heated.

I cringe every time I read about someone heating up their hunting or hiking boots to get the Sno-Seal to absorb.

B P Arn said:

It is almost always a very bad idea to heat leather. Heat will harden leather, but also leave it brittle and prone to cracking. Nothing that is expected to flex should be heated.

I cringe every time I read about someone heating up their hunting or hiking boots to get the Sno-Seal to absorb.

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His question was "how to harden leather", or at least that is how I read it.
Heating leather has been done for Centuries, the key is controlling the heat, don't cook it. That is why I stated "when the leather is Warm". Warm leather with absorb the wax quicker and more evenly, using a hairdryer rather then heat gun helps to not over heat it.

I have cared for Leather Cantines and Black Jacks (leather tankards) for years using heat to reseal once the beeswax or brewer's pitch wears away - Never a problem with cracking. My current black jack is almost 20 years old now and has been retreated MANY times, using a hot gun....I don't have original only because it was stolen during a party onboard the Star of India.
Wet forming, in hot water, is also an age old method, done several pieces, some followed with beeswax treatment and others not; have pieces several years old and no ill effects.

I like to naturally 'dye' veg tan in the sun - get some Great colors, takes a Long time; moisten with mineral oil and let the sun Bake it to a golden brown then a nice dark brown - just like human skin only since the cells are Dead it don't fade! I have baked leather this way in 100 degree direct sun for up to eight weeks; still good with no cracking after several years (key; treat it with a final coat of mineral oil when done, then after building the piece I like to give it some Pine Pitch leather conditioner)

Warming is fine, just don't apply constant heat above 135-140 degrees F, or it will be like a slow bake in a crockpot. Where a lot of folks mess up is with boots or other leather gear that gets wet in the rain or other water source. They try to fast dry by sitting or hanging the item near a wood stove or heater, never warm in order to dry. Sure it will dry faster, but as the water evaporates it carries tannery oils and the natural oils away with the evaporation then these need to be replaced. Say for instance, you place your boots by the fire in the evening so they will be dry by morning, yes they will dry but dry too fast. Leather can be damaged this way and the damage can never be corrected.

Yes, leather for boots, bags, coats, belts, etc need to dry out natural, then a good leather conditioner applied else they will lose all their oil and crack.
I have managed to revive some severely dried and cracking leather with Montana Pine Pitch products (others out there work too); a 40+ year old Glovers Palm so dried a cracked I thought for sure it was lost - today I still use it and it's like new once I replaced the lacing, and I have used it on several rifle straps of some CW reenactors who dont take care of their gear and was about to have the strap tear right off...they were however a bit upset that now they don't 'look worn out'.

But the OP did want to know how to "harden leather"; commonly done for some items.
I have two sword sheaths (cutlass size) one I made about 20 years ago, the other about 15 years. Using 4-5oz belly cut veg tan I soaked in near boiling water (dont know the temp but too hot to hold your hand in), waited untill the leather was soaked clear through and the leather became soft, almost putty like. Then with the sword thoroughly oiled and wrapped in Seran Wrap and tape, I quickly (speed is a must) stretched it around the blade, molded the seam and clamped it al down to dry...naturally, overnight.
After removing the clamps, punching and sewing the seams, I once again, with a hot hairdryer, warmed it up and painted in the melted beeswax.

I have carried each of those swords for years now, in parades, miles and miles of walking through events, many tall ships, even a couple movie shoots and several bars and parties. One in particular (the oldest) has taken a few ducks in the salty water of the ocean. Both are as good today as the day I made them - No cracking at all.
But I must confess, one had the tip of the sword eventually wear through so I have since glued a metal tip to the sheath (both swords are razor sharp).

But as mentioned; do not Cook, Boil the leather, it will revert to raw hide but without the strength it originally had before tanning. Also depends a lot on the leather and tanning method - suede usually turns to the consistency of wet cardboard or even just fall apart, some chrome tan I have seen just shrivel up and when dried it is hard as a rock and will Not soften up again.

When I make knife sheaths I use 5 to 9 once veg tan leather, let it soak in the sink for fifteen minutes, then dry it off on a towel and let it sit over night in a plastic bag. Then I mould it around the object (which is wrapped to prevent water damage) and let it dry naturally, which can take a day or two. It dries very hard.

Here's a good video on the subject:

Skidmore's is good for treating veg tan leather. The cream will add oils to old leather and condition it, but it will soften it as well. Their waterproofing treatment will not soften the leather and is best applied to leather that has been warmed with a hairdryer. I find this works better than straight bee's wax. (Make sure it's pure bee's wax, because a lot of "bee's wax" is mixed with paraffin.) Skidmore's is a mom & pop business, so you can feel good when you purchase directly from them.

https://skidmores.com/product/leather-cream/

piperdally said:

When I make knife sheaths I use 5 to 9 once veg tan leather, let it soak in the sink for fifteen minutes, then dry it off on a towel and let it sit over night in a plastic bag. Then I mould it around the object (which is wrapped to prevent water damage) and let it dry naturally, which can take a day or two. It dries very hard.

Here's a good video on the subject:

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If all you're doing is wet molding it, there's no need to get it that wet or wait that long to mold it. Dunk it, mold it, should be dry overnight.

GYJ said:

If all you're doing is wet molding it, there's no need to get it that wet or wait that long to mold it. Dunk it, mold it, should be dry overnight.

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If that works for you, great. In my experience a more thorough process works best. YMMV

Try a little Viagra on it.

RanchRoper said:

Try a little Viagra on it.

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Tried that, but it only last 6 to 8 hours.

Some years back I received a box of "scrap" leather of different thicknesses and colors. I made shoulder bags and ball bags with it and it worked great. For the ball bags I put them in hot water and after taking them out filled them with shot and allowed them to dry naturally. I have no idea what tanning processes the leather went through but they came out being stiff all the way to being hard as wood. Perfect for my usage. In all cases the ball bags were quite stiff when made of thinner leather and like wood if slightly heavier leather. Never put any kind of oil or wax on them and they've stayed very stiff for quite a few years and have been out with me hunting a lot. For drawstring bags I used some old buckskin for nice pliable pouches.

B P Arn said:

It is almost always a very bad idea to heat leather. Heat will harden leather, but also leave it brittle and prone to cracking. Nothing that is expected to flex should be heated.

I cringe every time I read about someone heating up their hunting or hiking boots to get the Sno-Seal to absorb.

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I've found that boiling it results in considerable shrinkage.

I soak the finished item (sheath, holster, etc.) For at least 15 minutes in warm water then insert the knife or whatever into it BUT FIRST wrap the knife in clear kit hen wrap. Then I pacage it with a Food Saver and leave it for a few hours or overnight. Remove and let it dry completely with the knife still in it. It will be stiff and form fit.

On knife sheaths I have sometimes done this process before stitching.