ericw93•1mo agoProlific Poster

I always thought the old 'quench in urine' thing was just a gross story, but a guy at the Montana forge meet last weekend showed me a real 18th century document that listed it as a hardening step for certain tools.

4 comments

4 Comments

What kind of tools did the document say it was for? I've heard it was sometimes used for files or springs. Did the guy have any idea why urine over water or oil?

grantw411mo ago

Urine's acid helps cut steel, water just rusts it.

margaret7361mo ago

Hold on, "urine's acid helps cut steel" is a huge overstatement. The ammonia in old urine might help break down rust or act as a light cutting fluid, but it's not actively cutting the metal. Water with a proper soap or oil works way better for lubrication and cooling without the mess and smell.

davis.olivia6d ago

The ammonia in old urine definitely breaks down rust. I had an old timer tell me once he'd soak rusty files in a bucket of it overnight and they'd come out cleaner than anything he could buy at the store. Never tried it myself though.