Some chemistry students and their teacher have been experimenting with
various leather tanning processes.
As their teacher, this has been a good way for the students (and me)
to learn patience, chemistry, and about dealing with many variables at the same
time.
Here are the latest results using Krome-tan as the tanning agent.
(The actual paper is in a more readable format, but the format won't
hole when it is entered here.)
Any suggestions of criticisms will be apprediated.
Thanks Bruce Rittel for your comments on the last installment.
Tanning an antelope hide with Krome-Tan (1-23-01)
Hide
We started with the back 1/2 of an antelope hide that had been salted and stored for some months.
It was washed, then soaked in clean water for 1-2 hours. It became soft and pliable.
De-hairing solution (50 g lye in 5 gal water)
The hair slipped well after 24 hours and was removed by pushing it off with a small wooden block.
The de-haired hide was washed in running water for 2 hours, then placed in the pickling bath.
Pickling solution (20 ml 37% HCl (muratic acid)+ 300g salt in 1 gal water) Ph 1.3
After 12 hours, the Ph was tested and found to have risen to 3.
10 ml of 37% HCl was added and the Ph dropped to about 1.5.
After 24 hours in the pickle bath, the hide was fleshed with a rotary wire brush. then put back in the pickle bath for another 24 hours.
The fleshing didn't look complete, so it was fleshed again with the rotary wire brush, then put back in the pickle for another day.
It was neutralized with baking soda for 1 hour, then rinsed 15 minutes with agitation.
The damp hide weighed 2 pounds.
Tanning solution (50 g Krome-tan in 200 ml water) and (150 g salt in 1 gal water)
1/3 of the krome-tan solution was added to the salt water and the hide placed in it. It was stirred frequently and kept luke-warm by setting it near the radiator. The Ph was 4.
After 12 hours, the solution was nearly clear so another 1/3 of the Krome-tan was added.
After 18 more hours, the solution was nearly clear again so the last of the krome-tan was added.
The hide was left another 24 hours in the solution (still near the radiator).
A small piece removed and dried. It was soft and supple and very light colored.
The hide was then removed, rinsed well, oiled with neatsfoot oil and dried near the fireplace. It was "broken" frequently while drying, but a few spots became hard anyway. The color was a nice, light, blue-gray except where the oil had soaked through. The oil probably should have been used more sparingly. Most of the leather was well tanned, but there were some stiff spots. It probably should have been left in tanning solution longer.
It was washed in the washing machine to remove the excess oil.
15 g of krome-tan was added to the tanning solution and the hide was soaked another 24 hours.
This time it was dried without oiling and with little breaking.
Results
The leather is soft and supple all over. The stiff spots are now soft.
The color is now a darker green than before. We liked the color better the first time it was dried.
It feels strong and durable.
It is considerably thicker than a previous antelope hide that was tanned with Lutan-F.
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I am hoping you take criticism positively - at least that how I intend it when I answer, and in this case, open up other options that may be helpful in the future.
OK - I get the impression you're stuck with Antelope skins, so I wont say anymore about it, except WT Deerskins are usually better for experimentation.
I would shy away from using Lye for dehairing. I use Hydrated Lime like the leather industry does. It simply does a much better job, particularly in loosening the small fine hairs that sometimes persist
Try to steer away also from Muriatic Acid as a pickling acid. Dangerous stuff - besides, its very harsh on the grain side of the finished leather. Use Sulphuric or Formic or Saftee Acid in the future. The leather industry uses Lime and Sulphuric acid. The only time they use Muriatic is when doing Alligator skins - to vbreak down the cartlidgeous material in the backs.
That Ph jump from 1.3 to 3.0 was the result of not "killing" the Lye in the skin. You need to "de-lye" it more thoroughly!
Leave the skin pickle thoroughly before fleshing it. Dont pull it out prematurely and keep picking at it. Wait 3 days, then pull it and do it in one operation.
Chrome typically tans best at about a 3.5 Ph level. Your feeds were correct.
STOP using just plain neatsfoot oil and buy a "Tanning Oil"! You need penetration, and plain ole neatsfoot is a surface oil. Also - there is no such thing as using oil sparingly. You need lots of oil to provide lubrication and to keep the size of the dried skin when its finished.
As a check for full tannage - cut a sliver from the edge and check it for blue all the way across its cross-section.
Dont wash it after tanning - rinse it with water. You may wash out a lot of the oil if you use a detergent.
Try to only oil at the end of the tanning cycle - not before!
If you want to mute the blue-green color of your leather try re-tanning it (while its wet and before oiling) with a syntan like EZ-100! It gives the leather a powder sky blue color.
Best of luck! Nice project for students! Hopefully some of the other suppliers will give you a critique too!
Bruce Rittel
Rittels Tanning Supplies
I am hoping you take criticism positively - at least that how I intend it when I answer, and in this case, open up other options that may be helpful in the future.
OK - I get the impression you're stuck with Antelope skins, so I wont say anymore about it, except WT Deerskins are usually better for experimentation.
I would shy away from using Lye for dehairing. I use Hydrated Lime like the leather industry does. It simply does a much better job, particularly in loosening the small fine hairs that sometimes persist
Try to steer away also from Muriatic Acid as a pickling acid. Dangerous stuff - besides, its very harsh on the grain side of the finished leather. Use Sulphuric or Formic or Saftee Acid in the future. The leather industry uses Lime and Sulphuric acid. The only time they use Muriatic is when doing Alligator skins - to vbreak down the cartlidgeous material in the backs.
That Ph jump from 1.3 to 3.0 was the result of not "killing" the Lye in the skin. You need to "de-lye" it more thoroughly!
Leave the skin pickle thoroughly before fleshing it. Dont pull it out prematurely and keep picking at it. Wait 3 days, then pull it and do it in one operation.
Chrome typically tans best at about a 3.5 Ph level. Your feeds were correct.
STOP using just plain neatsfoot oil and buy a "Tanning Oil"! You need penetration, and plain ole neatsfoot is a surface oil. Also - there is no such thing as using oil sparingly. You need lots of oil to provide lubrication and to keep the size of the dried skin when its finished.
As a check for full tannage - cut a sliver from the edge and check it for blue all the way across its cross-section.
Dont wash it after tanning - rinse it with water. You may wash out a lot of the oil if you use a detergent.
Try to only oil at the end of the tanning cycle - not before!
If you want to mute the blue-green color of your leather try re-tanning it (while its wet and before oiling) with a syntan like EZ-100! It gives the leather a powder sky blue color.
Best of luck! Nice project for students! Hopefully some of the other suppliers will give you a critique too!
Bruce Rittel
Rittels Tanning Supplies
Thanks for your time and expertise. That is the kind of information we have been looking
for since we started the project. We now have some deer hides available to
experiment with. We have one in progress right now that we are trying to tan
with EZ-100. We took it out of the EZ-100 solution after 22 hours and it dried
very stiff and hard. We put it back in for another 18 hours and it still turned
hard. It was worked a lot while drying, but just wouldn't soften.
We took a couple of small pieces of the same hide and tanned them in
Krome-tan and they came out great.
Our EZ-100 was mixed 1/2 oz per pound of damp hide (plus the salt)
and the Ph held right at 4 the whole time. Shall we go back in the EZ-100
for more time? What happens if the leather is over-tanned in EZ-100?
How do you recommend "killing the lye"? We theorized that muratic
acid would be ideal since it would form sodium chloride (salt) in the
hide which seems like a good thing, since all the other solutions contain lots of salt
We will try the lime on the next one. We tried a sulfuric acid pickle on an
earlier deer hide and the results were not good (probably not the acid's fault)
I was less concerned about the hazards of hydrochloric(stomach acid)
than sulfuric(battery acid). However both are so dilute in the pickle
that I'm not too worried, except when the kids are preparing them.
Anyway, since the HCl is damaging to the hide, we will try something else.
I see some formic on the shelf. Maybe that's next.
We are having a lot of fun with this and learning some chemistry too.
Thanks again.
Dave and the kids