I was digging through a lever gun or bullet casting website and read a pretty interesting article in using stump remover as a bluing agent but cannot remember the chemical in question. For some reason sodium nitrate is coming to mind but a quick glance at some stump removers in the store did not show anything with that. Anyone have any ideas on this? My google fu is weak on this, I have searched long and hard and the history is deleted everytime I turn off the lap top. I thought I was on leverguns.com or the beartooth site but cannot find it on either one.

My Google Fu is strong today.

http://shootersforum.com/showthread.htm?t=26290

And this one!!
http://beartoothbullets.com/tech_notes/archive_tech_notes.htm/58

Nitre blue is just a method of bluing using heat. There is no chemical reaction. The salts (potassium nitrate) are heated to about 700 degrees F and the parts submerged in it.

The parts are heated submerged in the nitrate to prevent oxidation, and are not exposed to the atmosphere, except when quickly taken out of the salts container and cooled in oil.

I think Brownell's sells the salts, along with directions on how to use it. Nitre bluing is not to be used on heat treated parts, because the high temperature, around 700 degrees F, will take the temper out of most tempered steel. It can and is used in conjunction with heat treating, for a part that has to be tempered at around 700 degrees F.

From what I have read about it, it is more of a decorative blue than a durable finish. I have seen pictures of small parts, screws, pins, barrel bands and other parts on rifles Turnbull (sp?) has finished. It is very attractive, but I don't think it would be practical to use it on an entire gun that will see much use.

And, it was not the type blue used on the high grade English guns.

I cannot get either of CRounds's websites to come up, but I recall reading on the label of a can of stump remover that it was just KNO3 (potassium nitrate). You may know it as saltpeter in the USA I think.

Potassium nitrate is used in niter bluing.

Niter bluing involves melting KNO3, then putting the clean metal in it. Be real careful that all parts are DRY -- and if it is hot and you are sweating, make sure a drop of sweat does not fall into the melted potassium nitrate.

I'm sure that a search for "potassium nitrate bluing" or "saltpeter bluing" would get some hits for you.

Make sure you remove all springs because KNO3 melts at about 600F and that temp will kill a spring.

Best of luck (and do not burn yourself!)

John

Ah, I see that 1234567 posted while I was checking the melting point of KNO3!

John

Damn I spent a lot of time looking and not seeing it. Thanks again to all.

I am not a 'Smith, nor do I play one on the internet or TV, but I do know most 'smiths will not nitre blue heate=treated parts for the reason de-scribed above

600 is not that hot for steel. I think that would still make for some fairly hard stuff. Don't know off-hand what temp they draw back spring steel but it has be up there somewhere. I know you can go to 1000 on CM steel and still keep it in the high 30s or low 40 on the C scale.


a quick search turned up only a few tables but for simple high-carbon steel (1084, 1095 etc) 700f is the ideal tempering heat. Music wire springs is likely a lower temp as it has a higher tensile strength.

Depends on the steel and the application. Ferinstance for 4140, a common steel:

Temper Rockwell C
------ ----------
400F........52
800F........42
1200F.......25

These numbers are VERY approximate. I don't think I'd want to deviate from the heat treatment engineered into a product without a good, hard think. Particularly if it involved a lot of PSI. You're essentially re-engineering the product. I'm no oracle on the subject but carbon steel springs are commonly tempered around 700F, more or less, sometimes appreciably less depending on steel and application. So if you bring a finished spring up to 700 you may change the character of the spring. Or maybe not.

I have that temper table, what I didn't learn is what is the ideal hardness for a spring. In any event, I don't think it will hurt anything other than springs to get them that hot. My rifle action is CM steel- I am guessing it is 4140 but maybe 4340 and was heat treated at about 975 by the manufacturer. 700 wouldn't hurt it at all.

It's too easy to cold rust blue, hot caustic blue, or Parkerize to mess around with hot nitre.