Black oxide coating

[Ray C]

No sign of the threaded rod yet... Maybe tomorrow...

Ray

 

[Tony Wells]

I have about 40 gallons of H3PO4 and MnO2 with 7kw electric heat in it to take care of my problems like that. Works good about 200°F. A good degrease in some NaOH solution, also hot, and a couple of rinses...voila, nice and dark, with a bit of oil.

 

[Ray C]

I have about 40 gallons of H3PO4 and MnO2 with 7kw electric heat in it to take care of my problems like that. Works good about 200°F. A good degrease in some NaOH solution, also hot, and a couple of rinses...viola, nice and dark, with a bit of oil.

Man, my community association would be on my back like a duck on a june bug if I had those kinds of chemicals around... Hoping to move into a 1200 sqft industrial space at the end of the summer...


Ray

 

[Tony Wells]

Ah, but Ray, this is oilfield country, and I am rural....besides, I am responsible with the waste, so no problems. Most of the engine builders here have gotten rid of their caustic vats though.....don't want to pay the disposal. They are using either an oven or a vapor degreaser now.

 

[chips&more]

I have found that the formula “lye, potassium nitrate, water and heat it to 270° F and for about 30 minutes” works EXCELLENT, EXCELLENT and more EXCELLENT! But, DO IT OUTSIDE AND STAND UPWIND! Just do a Google with the search words “bluing lye potassium nitrate” and you should get hits with all the help on details. The potassium nitrate is actual pretty easy to get, some store bought tree stump removers have it as 100% ingredients of the stuff. The cold bluing NEVER worked for me. But this hot process with very inexpensive chemicals gives fantastic results for the home shop machinist!...Good Luck.

 

[Tony Wells]

Potassium Nitrate also known as Saltpeter if I remember my black powder days. And yes, that method works. I have seen great results from it. As always though, the proof is in the prep.

 

[John Hasler]

Potassium Nitrate also known as Saltpeter if I remember my black powder days. And yes, that method works. I have seen great results from it. As always though, the proof is in the prep.

Do you have a reference for this process? I can find discussions of the use of melted saltpeter for blueing but not its use in water solution.

 

[benmychree]

The very best method for bluing and blackening is to take a 50/50 mixture of sodiun nitrate and potassium nitrate and melt it in a container to between 600 and 650 degrees; you simply immerse the item in the bath until the desired color is reached, which is a matter of minutes. The part need not be clean, as the nitrate salts will burn off any oil or fingerprints that may be present, and this makes a very rust resistant finish. This was titled US Armory method of bluing in an American Machinist technical article. I first saw that it worked when I was doing heat treating in the shop where I apprenticed back in the 1960s, where they used a tempering bath that had a set point controller to regulate bath heat; I noted that articles that were ground after tempering and may have been tested as being over the desired hardness and subsequently re tempered at the higher temperature came out of the bath with the colored finish; this happens while the piece is under the surface of the bath, and has nothing to do with temper colors that would be created by exposure with the air when heated. More recently I found the "recipe" in an American Machinist Shop Notes article. When my apprenticeship shop closed (Kaiser Steel Napa Plant) I boughtall the heat treating equiptment including about 1/2 barrel if the salt mixture. This mixture is the lowest melting salt mixture known, it will stay liquid down to about 275 deg. F.

 

[classicrestoration]

I've had good results with Caswell's black treatment. Use it for small parts like lock washers. A bit time consuming as the penetrant/sealant solution looks best after several days of air drying. In addition, lightly bead blasting the parts first helps to give it a truer flat black oxide appearance.

 

[John Hasler]

The very best method for bluing and blackening is to take a 50/50 mixture of sodiun nitrate and potassium nitrate and melt it in a container to between 600 and 650 degrees; you simply immerse the item in the bath until the desired color is reached, which is a matter of minutes. The part need not be clean, as the nitrate salts will burn off any oil or fingerprints that may be present, and this makes a very rust resistant finish. This was titled US Armory method of bluing in an American Machinist technical article. I first saw that it worked when I was doing heat treating in the shop where I apprenticed back in the 1960s, where they used a tempering bath that had a set point controller to regulate bath heat; I noted that articles that were ground after tempering and may have been tested as being over the desired hardness and subsequently re tempered at the higher temperature came out of the bath with the colored finish; this happens while the piece is under the surface of the bath, and has nothing to do with temper colors that would be created by exposure with the air when heated. More recently I found the "recipe" in an American Machinist Shop Notes article. When my apprenticeship shop closed (Kaiser Steel Napa Plant) I boughtall the heat treating equiptment including about 1/2 barrel if the salt mixture. This mixture is the lowest melting salt mixture known, it will stay liquid down to about 275 deg. F.

You don't add any manganese dioxide?