Black Oxide Test

[aliva]

Best blue/black is the US armory procedure, uses a 50/50 mixture of potassium nitrate and sodium nitrate melted in an iron or steel pot which is clean, not rusty, the mixture is raised to 900 deg.F and treated with manganese oxide to precipitate undesireable elements, the temperature lowered to 600-650 deg. F, the articles to be blued are immersed in the solution after being oiled, no prior cleaning being necessary, after a few minutes, the articles are removed and the color observed as to the color desired, from blue to black, if left in the bath too long, the color may degrade, after the color is reached, the articles are removed and quenched in cold clean water, then into boiling water to remove any salt adhereing on them, and finally into hot oil, time in the niter bath should not exceed 4 or 5 minutes, if longer than, the finish will be degraded to a dirty grey.
I have used this process, and it is quite durable, equal to factory gun finishes, the temperature used produces a spring temper, and the bath can be used for general tempering use at appropriate temperatures, once melted, the bath can be used at much lower temperatures for tempering use.
This information came from an American Machinist reference book sheet

That's a very long procedure and I think a little too hazardous for the hobby machinist.

 

[benmychree]

Long procedure in what way? Really quite simple, not toxic particularly, simple safety equipment makes it safe. Once set up, it is a fast process giving excellent results.

 

[aliva]

Long procedure in what way? Really quite simple, not toxic particularly, simple safety equipment makes it safe. Once set up, it is a fast process giving excellent results.

I consider 600-650F hazardous. But that's me.

 

[ChazzC]

Caswell does recommend a sealer Brownells does not

Brownells’ instructions for Oxpho-Blue recommend rubbing “briskly” for best results and note that it is intended for touching up an existing blued surface. Blued guns are usually lightly oiled.

Various write-ups in Brownells Gunsmith Kinks books recommend using clean/oil free steel wool to apply cold bluing solutions, followed by rinsing and oiling.

I made some 1/4-20 / 10-32 Tnuts a while back, cleaning them with Acetone and warming them before soaking in Oxpho-Blue. I scrubbed the solution with a toothbrush and washed with hot soapy water before coating with light machine oil which I left on overnight before wiping. I was very happy with the results:

 

[MrWhoopee]

I've used the process described by @WobblyHand. It works well if repeated enough times. My only objections are how long it takes and the salt pits the parts. I found a refinement of the formula using less salt and some vinegar with the peroxide, if I can only find it again.

 

[atunguyd]

We have a product here called kalgard, pretty much the same as cerekote and also for firearms. I use that these days.
Sandblast, Degreaser, spray then bake in the oven. All done and a perfect finish every time. All my home built tooling gets it now days

Sent from my SM-S908E using Tapatalk

 

[WobblyHand]

I've used the process described by @WobblyHand. It works well if repeated enough times. My only objections are how long it takes and the salt pits the parts. I found a refinement of the formula using less salt and some vinegar with the peroxide, if I can only find it again.

First learned to do it based on one of your posts, and followed the link you provided. If you can find that reference, please post it. I do think that the surface quality could be better, but it's great for little stuff like tee nuts. I'm sure that the hot salt bluing is better, but the cold method is a bit safer and the materials are easier to source.

 

[MrWhoopee]

I've used the process described by @WobblyHand. It works well if repeated enough times. My only objections are how long it takes and the salt pits the parts. I found a refinement of the formula using less salt and some vinegar with the peroxide, if I can only find it again.

I found it!

1 cup hydrogen peroxide
1/4 cup vinegar
1 tablespoon salt

 

[pontiac428]

I am determined to put together a hot salts bluing setup. Haven't got there yet, because I have no gas burners on hand from other hobbies. Still looking for a free one.

Until that day comes, I have had by far the best results from cold selenium bluing, particularly with Oshpo blue. It is much tougher than the Birchwood Casey equivalent, and much darker. A little bit of heat (just warm to the touch) will kick any chemical process into high gear, so that's a given.

 

[DavidR8]

I am determined to put together a hot salts bluing setup. Haven't got there yet, because I have no gas burners on hand from other hobbies. Still looking for a free one.

Until that day comes, I have had by far the best results from cold selenium bluing, particularly with Oshpo blue. It is much tougher than the Birchwood Casey equivalent, and much darker. A little bit of heat (just warm to the touch) will kick any chemical process into high gear, so that's a given.

Hey John, I keep an induction hot plate in the shop for heating up degreasers for the ultrasonic cleaner and I plan to use it to heat up the hot salts bluing mixtures. The first time I ever used it I was stunned at how quickly it boiled water. Like under two minutes to boil a few quarts of water.
Mine has a handy temp setting also so if I need a specific temp I can dial it in.