Great -- an opportunity! The last time this came up I said it was the last time I was going to write another post on the issue -- from now on I'm just reposting the last rant.
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Arghhhhhhhhhhhh! This canard has come up once too often -- *this* time I'm saving this rant and in the future I'll post it at every opportunity and won't have to keep writing it over.
LEATHER SHEATHS DO NOT CAUSE RUST. IT'S A LIE SPREAD BY UNSCRUPULOUS MERCHANDISERS.
Leather naturally absorbs some of the oil you put on your knife or gun and helps prevent rust. Your knife is safer from rust in a leather sheath than anywhere else.
Some companies buy the cheapest leather they can get to make sheaths. A few years ago some imported leather appeared on the market that had not had all the tannic acid rinsed out of it at the end of the tanning process. *THAT* LEATHER CAUSES RUST. When manufacturers became aware of the problem, some of them stopped using the improperly tanned leather -- but others didn't want to pay for leather that had been properly tanned. They found a cheaper solution: use the shoddy leather and tell their customers "Leather causes rust."
If you suspect you may have a sheath made of that leather, rinse it in water for a couple of hours and then (after it's dry) apply whatever leather dressing you like.
I have a knife I bought in 1973 and kept in the leather sheath ever since. I stored it in the sheath for years at a time without even taking it out to use it. It's not stainless steel and it never rusted. If any manufacturer tells you leather causes rust don't believe ANYTHING that manufacturer tells you.
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There should be a special place in hell reserved for those crooks -- where they have to wear clothes impregnated with acid, and if they complain the devil tells them, "Clothes burn skin."
-Cougar Allen :{)