Anyone know of an effective long lasting way to blacken all thread……

[Firstram]

I have don niter bluing/blackening according to the US Aromory process with a 50/50 mixture of sodium/potassium nitrate heated to about 600-650 deg F. items need not be excessively cleaned and should be lightly oiled before immersion in the molten salts, it takes only about 5 minuities for small items to form a very durable finish. I have posted this many times in more detail previously; this is the real thing, all other recipes are second to 3rd or 4th rate or beyond; the comparison to soot is a good simile.

Why do you need to lightly oil the parts first?

 

[Eddyde]

FTR, if you need to remove galvanizing from threaded rod, bolts or anything else, simply submerge it in a strong Hydrochloric Acid solution, commonly available as Muriatic Acid. It will strip all the galvanizing off, in minutes.
EDIT: This should only be done outdoors as it generates explosive gases and toxic vapors. Also, use proper PPE, goggles, gloves, etc.

 

[pontiac428]

FTR, if you need to remove galvanizing from threaded rod, bolts or anything else, simply submerge it in a strong Hydrochloric Acid solution, commonly available as Muriatic Acid. It will strip all the galvanizing off, in minutes.

Just don't do it while smoking.

 

[Flyinfool]

While it is probably not the "best". I have used Brownells Oxpho Blue on zinc plated hardware and it does turn it black. Just wipe it on, let dry and buff the grey stuff off. I have used this to darken the hardware on hunting stands and it is still black after many years out in the woods. QUick easy and not real expensive.

 

[WobblyHand]

Just don't do it while smoking.

The chemical reaction releases hydrogen gas and little droplets of hydrochloric acid in the air. The HCl is not so good to breathe. So don't take a deep breathe of this stuff.

The hydrogen is extremely flammable. Lower explosive limit of hydrogen in air is 4%, upper explosive limit is 75%. Hydrogen gas is rarely used in lighter than air craft or balloons because of this. The Hindenburg disaster of 1937 in NJ effectively ended the use of hydrogen for blimps and dirigibles.

That being said, just strip the zinc with HCl (hydrochloric acid) outdoors and you will be fine. Don't smoke or make sparks nearby when releasing hydrogen.

 

[benmychree]

Why do you need to lightly oil the parts first?

The beauty of the process is that it does not require hardly any cleaning of the parts to be blackened/blued as do other processes; I do not know why the instructions say to coat the articles in light oil, but mu observation is that it visibly burns off when submerged in the bath, which is clear as melted. I observed the effect of the bath, which we used for tempering in the shop where I apprenticed back in the mid 1960s, when an article had been ground to test for hardness, and it was too hard and needed to be retempered, it would turn blue/black at a temperature of 600 - 650 deg. F, the shade depending on the length of time in the bath, not the temp.; much later on I found an American Machinist book od shop notes that gave all the details and attributed it to the US Armory.

 

[pontiac428]

The beauty of the process is that it does not require hardly any cleaning of the parts to be blackened/blued as do other processes; I do not know why the instructions say to coat the articles in light oil, but mu observation is that it visibly burns off when submerged in the bath, which is clear as melted. I observed the effect of the bath, which we used for tempering in the shop where I apprenticed back in the mid 1960s, when an article had been ground to test for hardness, and it was too hard and needed to be retempered, it would turn blue/black at a temperature of 600 - 650 deg. F, the shade depending on the length of time in the bath, not the temp.; much later on I found an American Machinist book od shop notes that gave all the details and attributed it to the US Armory.

I think the emphasis on cleaning is for an ultra fine finish, like the excellent blues found on Brownings and Colts after the war. The caustic hydroxide will break down the oils very quickly at that temp.

I knee-jerked on the blackening zinc plating a bit, because my brain said that's not steel- But, duh, zinc phosphate/chromate is indeed a stable and deep black. Also my bias that construction grade all-thread is the lowest rung on the hardware ladder when it comes to precision threads, and galvy or hot dip zinc is a rather lumpy, coarse finish. I don't think I gave that idea the consideration it deserved when I commented.

 

[WobblyHand]

I have don niter bluing/blackening according to the US Aromory process with a 50/50 mixture of sodium/potassium nitrate heated to about 600-650 deg F. items need not be excessively cleaned and should be lightly oiled before immersion in the molten salts, it takes only about 5 minuities for small items to form a very durable finish. I have posted this many times in more detail previously; this is the real thing, all other recipes are second to 3rd or 4th rate or beyond; the comparison to soot is a good simile.

What do you melt the sodium/potassium nitrate in? Any special concerns when starting the initial heating to drive off moisture?

 

[benmychree]

The armory process is quite good from the standpoint of protection from rust, the utter lack of cleaning/prep that other processes require and leaves a finish that is quite nice, and requires little care in process, and the two chemicals used seem to have little if any toxic effects, of course a splash could burn you.

 

[benmychree]

What do you melt the sodium/potassium nitrate in? Any special concerns when starting the initial heating to drive off moisture?

Melting can be done in a steel or iron vessel. moisture is not a problem, it will boil off before melting starts. Manganese dioxide is used occasionally to cleanse the bath if blotchiness is noticed. I use a setpoint temp. control to regulate the temp. with the thermocouple immersed in the bath.