I used to use:
5# lye
4# Sodium Nitrate (you can use Ammonium Nitrate as well)
1 gallon of water (distilled)
Blues at 265/275F
Nice blue/black finish very similar to Brownells salts
Careful when mixing,,lot's of heat generated and the soln can 'boil' and splatter as it's being mixed. Eye/ full face/cover all skin. Even then it'll eat right through most cloth and even leather when hot.. Keep the kids .pets and nosey neighbors away.
It's not a spectator sport, there's no running away from the burns it can inflict in a matter of a split second should any part of your equipment topple especially when it's near 300F.
Clean up is no fun and the evaporating water from the process carries the salts with it and leaves a layer of them deposited on everthing in site. They then absorb water from the air and become 'wet'. Any encrusted steel will rust,,wood will become soggy.
Needs good ventilation or done outside.
You can get away with very small bluing runs w/o too much mess but a large long tank will spew a lot of water and salts into the air and it'll build up quickly.
For small parts like you mentioned, doing the bluing in a surplus 50cal ammo can works well. Remove the paint first of course. After the salts have cooled down when done you can simply put the cover back on and it's sealed back up for the next run. Unsealed, the 'tank' full of salts will absorb water from the air.
Not a kitchen DIY project. It eats aluminum quickly.
Have fun...!
Now I just rust blue!
