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Oil for black oxide finish

pcm81

Cast Iron
Joined
Apr 10, 2014
Location
USA FL
So, I've been playing with some hot caustic bluing, the basic formula is 5lb of sodium hydroxide and 2lb of sodium nitrate per gallon of water. Bath is operating at 290 degreed F.

After bluing is done i used to just leave parts in oil overnight to let them soak up the oil. Recently i tried and very much like a new method. The new oiling method consists of placing parts in the oil container and the oil container into a vacuum chamber. Then i pump the air out down to about 5000 micron and let the oil outgas. This pulls moisture as well as air out of black oxide finish. So far i only experimented with used vacuum pump oil not a true water displacing oil or oil with corrosion inhibitors added to it. My worry with "proper" black oxide oils is that they may be a mixture of oils and solvents, which would separate under vacuum. I see the black oxide oils advertised as "dry to touch" which tells me that they have solvents in them, which evaporate at STP. Can anyone recommend a "proper" black oxide oil which can survive vacuum? My worry with continuing using use vacuum pump oil is that the vacuum pump oil is hydrophilic, so it will absorb moisture from the atmosphere and bring it into black oxide finish, ultimately doing the opposite to what it is intended purpose is in the oxide finish.
 
So, I've been playing with some hot caustic bluing, the basic formula is 5lb of sodium hydroxide and 2lb of sodium nitrate per gallon of water. Bath is operating at 290 degreed F.

After bluing is done i used to just leave parts in oil overnight to let them soak up the oil. Recently i tried and very much like a new method. The new oiling method consists of placing parts in the oil container and the oil container into a vacuum chamber. Then i pump the air out down to about 5000 micron and let the oil outgas. This pulls moisture as well as air out of black oxide finish. So far i only experimented with used vacuum pump oil not a true water displacing oil or oil with corrosion inhibitors added to it. My worry with "proper" black oxide oils is that they may be a mixture of oils and solvents, which would separate under vacuum. I see the black oxide oils advertised as "dry to touch" which tells me that they have solvents in them, which evaporate at STP. Can anyone recommend a "proper" black oxide oil which can survive vacuum? My worry with continuing using use vacuum pump oil is that the vacuum pump oil is hydrophilic, so it will absorb moisture from the atmosphere and bring it into black oxide finish, ultimately doing the opposite to what it is intended purpose is in the oxide finish.

Black Oxide or blue-ing is "supposed to be" only a change in the outer valance electrons of an Iron atom that changes which Isotope name it presents for ID when buying booze or wotever Iron atoms do when married to a greedy round-heeled b***h like Oxygen.

In theory, there isn't much place for an oil to GO, given the molecule sizes. In practice, of course, the oil is important.

How much of that is "in the pores" or on the surface as a molecular film I leave to those with electron microscopes.

Must be a few scholarly articles out there?

Comes to one of the sometimes-alternatives, Parkerizing, even the US Marines get into the publishing biz. Black Oxide lore should not be new ground, either.

Meanwhile not ALL vacuum/refrigerant lubes are hygroscopic. Far from it. Look up the old MIL-SPEC "ORC" series. "Wax free" straight mineral oil, mostly.

Then again? A "wax-thrower" or a polymerizer may be just what you need. I've "Case Old Forge" HCS kitchen knives no longer in daily use forty years now that have stayed bright for being put away with the varnish generated by ignorant "pomace" (solvent extracted, then distilled, low/no fruit residue. "Extra Virgin AKA "first cold pressing" is lousy with organic acids) Olive Oil.

IF/AS/WHEN I NEED one, the cutting edge wants "rifled" to clear the "skin", but no more than that.

Vegetable-derived oils such as Linseed, Olive, Canola, are dead-wrong as lubes or coolants, That polymerization thing builds glue, varnish, AND/OR "food" for critters Real Soon Now.

For preserving non-precision-fit surfaces on seldom-used tools, OTOH? Hammer heads and wooden handles, AND NOT Micrometers or calipers - I keep them handy in my shop.

:)

NB: if i must PAY for it, I'll take QPQ Black Nitriding ELSE ignorant hardened and ground bright finish any day of any week.

If I must DIY? Parkerizing - if tolerances permit it - isn't so much "better" as it is simply easier to not badly f**k up.

Black Oxide is only here at all on stuff I don't really much give a s**t about. HF "impact" sockets, mostly. It sorta shouts "poverty shows, you cheapskate!" .. and drools over even CHEAP bright plating.

HF or Kobalt may not have much of a wrench UNDER the skin, but they sure do make shiney eye-candy for the Joe Average "impulse purchase" rather well.


:)
 
The 'dry to the touch' feature might be from the use of an oxidizing oil, like boiled linseed, tung oil etc. as used for wood finishing. You'd get almost the effect of a varnish, which is probably a good idea, since black oxide, in itself, isn't that good at corrosion protection.

Linseed oil seems to have a pressure of 10-100 milliTorr (Micron Hg) at 25°C, so well within the range you are pumping down to.
 
The 'dry to the touch' feature might be from the use of an oxidizing oil, like boiled linseed,

"Oxidize" they certainly can do. See sloppiness of rushed preparation, Tutankhamun's mummy, fires in waste cans, etc.

What one wants, though is the less aggressive cross-linking AKA polymerization - AND NOT Oxidation nor spontaneous combustion heat levels from it.

Wooden hammer handles and gunstocks really common examples of long-standing. Raw-rubbed into fine woods or applied as paints with a pigment added, Linseed oil doesn't so much "dry" as it changes its very nature from liquid to a plastic. A "resin", early predecessor of, and functional cousin to, the ubiquitous Alkyd's we so often rely on in our paints, yet today.

Surely ruins yer month if mistaken for a lube oil!

:(

2CW
 
Thank you all for the replies.

The online research I did on black oxide suggests that its thickness is measured in single digit micro inches, which is ignorable thin as far as dimension change is concerned,however more than thick enough to form a layer that is thousands of iron oxide molecules thick. The porosity of this layer depends on ratio of magnetite to haematite in the layer. Higher temperature bath will produce more haematite and less magnetite. I can confirm this by observing reddish tint on a batch I did in 300+ degree bath vs a batch I did at 280-300 degree bath. Definitely like the 280-300 degree bath results better.

The oil sinks into magnetite matrix and provides corrosion protection by blocking oxidizing agents, like oxygen in the air, from coming in contact with iron in the part.

Someone mentioned parkerizing in this thread. that is a different process. Parkerizing deposits iron phosphate onto the surface and that iron phosphate layer creates a base for paint.

Neither parkerizing aka phosphating nor black iron oxide provide corrosion protection by themselves. In both cases corrosion protection is provided by oil or paint that is applied on top of the deposit. My concern here is the oil absorbing moisture from the air, hence rendering itself useless. My other concern s using the oil that is a not an azeotropic mixture of solvents and waxes, since i do not want the solvents to evaporate in my vacuum chamber.
 
Thank you all for the replies.
My concern here is the oil absorbing moisture from the air, hence rendering itself useless. My other concern s using the oil that is a not an azeotropic mixture of solvents and waxes, since i do not want the solvents to evaporate in my vacuum chamber.

I "think" I see the gain you are goaling for, but I'd suggest you find the best-performing oil first, then modify the vacuum pump, chamber, or perhaps just some part of the process to take best advantage OF the chosen oil.

Presuming this is for continuing production, dedicated chamber, etc...not just fewsies and done with whatever is already there, anyway.
 
I'm curious about your tank recipe. I've done a little gun bluing and my formula was 60% sodium hydroxide, 25% sodium nitrate, and 10% sodium nitrite. That's how I was taught so I've never changed it. One pound of the mixture would raise the tank boiling point two degrees. Once the color was achieved I wanted, the part went to a boiling water tank for a couple minutes, then directly to a room temp water displacing oil tank for another couple minutes. The part is then, covered with RIG grease and left overnight.
I wonder what the sodium nitrite does in my recipe?
What do you like about your vacuum method better than your previous way?
What is the end goal you would like to see?
How do you prep your parts before immersion? (high polish, bead blast, etc.)
Like I said, just curious.
 
What was the remaining 5%?

I'm curious about your tank recipe. I've done a little gun bluing and my formula was 60% sodium hydroxide, 25% sodium nitrate, and 10% sodium nitrite. That's how I was taught so I've never changed it. One pound of the mixture would raise the tank boiling point two degrees. Once the color was achieved I wanted, the part went to a boiling water tank for a couple minutes, then directly to a room temp water displacing oil tank for another couple minutes. The part is then, covered with RIG grease and left overnight.
I wonder what the sodium nitrite does in my recipe?
What do you like about your vacuum method better than your previous way?
What is the end goal you would like to see?
How do you prep your parts before immersion? (high polish, bead blast, etc.)
Like I said, just curious.
 
I'm curious about your tank recipe. I've done a little gun bluing and my formula was 60% sodium hydroxide, 25% sodium nitrate, and 10% sodium nitrite. That's how I was taught so I've never changed it. One pound of the mixture would raise the tank boiling point two degrees. Once the color was achieved I wanted, the part went to a boiling water tank for a couple minutes, then directly to a room temp water displacing oil tank for another couple minutes. The part is then, covered with RIG grease and left overnight.
I wonder what the sodium nitrite does in my recipe?
What do you like about your vacuum method better than your previous way?
What is the end goal you would like to see?
How do you prep your parts before immersion? (high polish, bead blast, etc.)
Like I said, just curious.

I'm curious about your tank recipe. I've done a little gun bluing and my formula was 60% sodium hydroxide, 25% sodium nitrate, and 10% sodium nitrite. That's how I was taught so I've never changed it. One pound of the mixture would raise the tank boiling point two degrees. Once the color was achieved I wanted, the part went to a boiling water tank for a couple minutes, then directly to a room temp water displacing oil tank for another couple minutes. The part is then, covered with RIG grease and left overnight.
I wonder what the sodium nitrite does in my recipe?
What do you like about your vacuum method better than your previous way?
What is the end goal you would like to see?
How do you prep your parts before immersion? (high polish, bead blast, etc.)
Like I said, just curious.

The recipe for my mixture i got on Finishing.com. It seems to work, however to be honest i think the difference from one recipe to another does not result in it working vs not working, but rather fine tuning to how it works.

The two basic components to a caustic bluing bath is sodium hydroxide and sodium nitrate. The sodium nitrate reacts with iron to create ferric nitrate, which then reacts with sodium hydroxide to produce either haematite or magnetite. Additives to this basic mixture can add other atoms like chromium to the magnetite matrix, but atthat point you are not just creating black oxide layer, rather you are modifying that layer for additional qualities. The single most important parameter is the temperature of the solution. With too low of the concentration the solution will boil below 270 defrees F and you will get zero deposit. With temperature above 300 degrees F the deposit will form too rapidly resulting in increasingly larger fraction of haematite being deposited instead of magnetite.

I have seen recipes with concentration of sodium hydroxide ranging from 4lb to 8lb per gallon of water and sodium nitrate or also nitrite ranging from couple ounces to 2.5 pounds per gallon. Concentration of the salts will determine the boiling point of the solution. I do not know if actual boiling is required to achieve good blackening or is simply a convenience to provide agitation while keeping temperature constant. I am tempted to side with the latter, because I have seen black oxide start to form around 270*f and solution did not start boiling until 300*f.
 
For me the starting boiling point is a way to regulate the strength of the solution. If I want to start the process at 295*, and I get a rolling boil at 291*, I know I have to add 2 lbs. of salts to increase the boiling point to 295*.
I have a chart that tells me how many ozs. of each 3 components to add to get 2 lbs.
And to be honest when I set up my own tanks the smallest container of sodium nitrite I could get was a 400 lb. drum. Sodium nitrite is the 10% ingredient, so I just use a commercial product now. Still get 1 pound will raise the boiling point 2 degrees.
 
For me the starting boiling point is a way to regulate the strength of the solution. If I want to start the process at 295*, and I get a rolling boil at 291*, I know I have to add 2 lbs. of salts to increase the boiling point to 295*.
I have a chart that tells me how many ozs. of each 3 components to add to get 2 lbs.
And to be honest when I set up my own tanks the smallest container of sodium nitrite I could get was a 400 lb. drum. Sodium nitrite is the 10% ingredient, so I just use a commercial product now. Still get 1 pound will raise the boiling point 2 degrees.

Be careful when giving advice like this. Adding 1lb to a 100 gallon tank is whole lot different than adding 1 pound to a 1 gallon tank... It all boils down to concentration, not quantity.
 
I too did a lot of home blacking on mostly shotguns and air rifles. In the beginning I bought the component parts of the bath but restrictions on oxidising chemical supply in the UK made them hard to obtain so I changed to commercially available salts.
I found the best way of working was to solvent degrease as best I could followed by a boil in alkali degreaser and then into the blacking tank, i controlled the temperature by adding water to the solutions, i cold water rinsed and then reblacked at a higher temperature. When finished I rinsed with cold water to remove most of the salts and then boiled the work in water and took it from the tank and allowed the water to evaporate for a minute before dipping in dewatering oil and allowing to cool.
I was taught that the oiling added durability to the finish and was an important part of the process.
While I accept that the finish is only very thin, I did find that the fitbof mating parts tightened up after blacking, I thought that it was the addition of oxygen etc that built up,the surface
 
Gun blue/black is common..I used to black gauges then finish the gauge dimension surfaces..they really looked sharp.

I used to sporterised 98s Mausers ..I would plug the barrel and wipe with alcohol..then wash with Babo powder cleanser and ver hot water..Quick dry and then use cold gun blue/black..they came out very good..

Lacquer thinner likely would have been better but I did not like the smell.
Today carb-cleaner might be good...
 
Sometime in effort tend tend to over engineer

So, I've been playing with some hot caustic bluing, the basic formula is 5lb of sodium hydroxide and 2lb of sodium nitrate per gallon of water. Bath is operating at 290 degreed F.

After bluing is done i used to just leave parts in oil overnight to let them soak up the oil. Recently i tried and very much like a new method. The new oiling method consists of placing parts in the oil container and the oil container into a vacuum chamber. Then i pump the air out down to about 5000 micron and let the oil outgas. This pulls moisture as well as air out of black oxide finish. So far i only experimented with used vacuum pump oil not a true water displacing oil or oil with corrosion inhibitors added to it. My worry with "proper" black oxide oils is that they may be a mixture of oils and solvents, which would separate under vacuum. I see the black oxide oils advertised as "dry to touch" which tells me that they have solvents in them, which evaporate at STP. Can anyone recommend a "proper" black oxide oil which can survive vacuum? My worry with continuing using use vacuum pump oil is that the vacuum pump oil is hydrophilic, so it will absorb moisture from the atmosphere and bring it into black oxide finish, ultimately doing the opposite to what it is intended purpose is in the oxide finish.
I wonder what advantage there is to submit the black oxide parts to the vacuum process since the atmosphere is neutral to the black oxide parts regardless of the amount of the reduced atmosphere. I would think a light mineral oil at normal atmosphere would work well. Since I feel the vacuum process, in my opinion, does nothing to draw the oil into the grain of the steel. I would also strongly consider oil with animal fats as part of the oil. Comments?

All The best
Roger 05/07/2008
 
I would also strongly consider oil with animal fats as part of the oil. Comments?
Time was, Whale oil, later "Porpoise jaw" oil were beloved for many discerning uses, firearms to fishing reels. Tallow was applied for other uses. Early-days "penetrating oil", hot exhaust manifold fasteners, for one.

The "deal" was that animal fats didn't polymerize the same way as (most) vegetable oils can do. They remain whatever they were for years. tears, and abuse.

OTOH? Organics can give rise to other organics, and that has generally been found not a good thing.

The bang-stick crowd have the products that actually work pretty well nailed.

Oil quite aside, hundreds of millions of military firearms, sidearms to cannon, have been done with Parkerizing instead of black oxide

Dumbest of all reasons. It's what JF works. Most especially for complex mechanisms, severest possible duty, genuinely critical use.

A Harbour Freight impact socket wrench set, OTOH?

REALLY HARD to find anything shittier or less dependable for rust prevention than black oxide.

So they don't even look for it.
 
I wonder what advantage there is to submit the black oxide parts to the vacuum process since the atmosphere is neutral to the black oxide parts regardless of the amount of the reduced atmosphere. I would think a light mineral oil at normal atmosphere would work well. Since I feel the vacuum process, in my opinion, does nothing to draw the oil into the grain of the steel. I would also strongly consider oil with animal fats as part of the oil. Comments?

All The best
Roger 05/07/2008

Vacuum helps to draw air out of the oxide film allowing oil to flow into those pockets. Without vacuum, viscosity of oil makes this a very slow process, since force of air trying to escape though oil is countered by surface tension and viscosity of oil. Vacuum also removes trapped moisture in oxide layer and oil.
 
Time was, Whale oil, later "Porpoise jaw" oil were beloved for many discerning uses, firearms to fishing reels. Tallow was applied for other uses. Early-days "penetrating oil", hot exhaust manifold fasteners, for one.

The "deal" was that animal fats didn't polymerize the same way as (most) vegetable oils can do. They remain whatever they were for years. tears, and abuse.

OTOH? Organics can give rise to other organics, and that has generally been found not a good thing.

The bang-stick crowd have the products that actually work pretty well nailed.

Oil quite aside, hundreds of millions of military firearms, sidearms to cannon, have been done with Parkerizing instead of black oxide

Dumbest of all reasons. It's what JF works. Most especially for complex mechanisms, severest possible duty, genuinely critical use.

A Harbour Freight impact socket wrench set, OTOH?

REALLY HARD to find anything shittier or less dependable for rust prevention than black oxide.

So they don't even look for it.

Black oxide does not offer rust prevention. Black oxide creates a porous layer for oil to sit in. Oil is the rust preventer.
 








 
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