Must we oil BLACK OXIDE finish?

A. Henry:

Oiling is absolutely required after black oxide. If you don't specify I would expect a service shop to apply their "standard" oil.

Most customers either go with an "oily" feel or as you mentioned "dry to the touch". If you have a preference I would supply that to the vendor.

A more in-depth answer may include how much protection it provides typically measured in salt spray hours or humidity chamber testing. These numbers don't necessarily guarantee performance in the real world but are useful to compare oils vs one another.

A. It sounds to me like your vendor used an oily finish oil. Not all oils will leave that tacky residue. Some oils are formulated to leave a dry-to-the-touch finish so as not to attract dirt once the part is in service. You may also want to look at using a water soluble oil that when mixed properly will leave a dry finish. Oh yeah, you do need to put some sort of rust prevent on the black oxide because the coating itself will only give minimal (1-2 hrs) salt spray corrosion resistance. With a good oil, you can easily get in excess of 80 hours salt spray resistance.

A. Hello Bruce,

I am assuming your parts are steel and yes it is the oil that provides the corrosion resistance on Black oxide coating for this material. Stainless will blacken does not require the oil, and the processing costs are similar to processing black oxide for steel. Other processes (black zinc, nickel etc..) are usually more expensive and alter the part dimensionally.

Good luck,

A. Bruce, typically an oil is applied to black oxide coatings to enhance its rust protection. The type of oil and the amount applied will determine if the treated parts are wet or sticky. The parts you received appear to have been treated with a viscous oil that makes them sticky. I suggest you contact the shop that applies the black coating and see if they could apply less of a lower viscosity oil. This type of oil will provide less rust protection than the current material but it help you to meet your performance goal of not allowing dirt to stick.

We typically recommend applying a water dilutable rust preventative oil over black oxide. That way, by increasing or decreasing the concentration of the oil in the water, we can vary the amount of oil deposited on the parts. At low concentrations, the treated parts are dry to the touch and will not collect dirt.

A. It is common to apply an oil based corrosion inhibitor to both black oxide and phosphate parts. Without this corrosion inhibitor, it is very likely the parts would develop rust while in transit or storage. If the screws are causing an oil residue to form in the screw gun tubes, your supplier may be applying too much oil or using a material that leave the screws too oily. My suggestion would be to request that your vendor apply less of the rust preventative to the parts.

A. Or you could request that the screws have a water soluble wax applied to them after Oxide versus the oil. I have seen this done in the past when oil is not acceptable with great results.

A. One more possibility is that the screws you are using have been "cold blackened" rather than receiving a true black oxide finish (see our FAQ on black oxide). Cold blackening has some advantages, but the finish is invariably very smutty because it's not a true oxide coating but a selenium smut that rubs off more readily than a true black oxide.

A. Unfortunately, that goal is questionable, Bill. It is the oil not the black oxide that provides the corrosion resistance. The oil can be very easily removed with a solvent, but the parts will rust almost instantly.

Bill,
Many black oxide chemical suppliers also sell dry-to-touch oils and waxes which can be used instead of 'oily' oils. Sometimes called rust preventatives.

A. I think that you can get by with just wiping it down with shop cloths or high quality paper shop cloths. If you use a solvent, you have a disposal problem.

A. Although there are many types and weights of oil and many types of grease, as far as I know the only difference is that the grease contains a fat or soap to keep it in place. I don't think that can hurt the black oxide coating; I don't think ordinary solvents have any effect on it either.

I am a little surprised that a wear surface like a ball screw would have a black oxide coating since it's not very durable. Sure it's not a salt bath nitriding (which is also black)?

A. Hi, Brian. You cannot leave them without oil or wax or they will flash rust in hours. You need to get the oil off in a solvent (maybe a vapor degreaser) and immediately apply a wax or dry-to-the-touch oil. Let a plating shop try a few dozen and see if they solve the problem. Maybe they are salvageable without redoing the finish completely.

Is the "oil" essentially transparent or is it sooty? I hope it's real hot black oxide, and the oil is clear, because if it's a selenium-based cold blackening process rather than true hot black oxide, I doubt the batch can be made smut-free without complete stripping and re-processing. Good luck.

Regards,

A. I have seen so many people try to use black oxide on furniture and other house hold goods and it just never works. Black oxide or blueing is a finish that is to be used on toys like guns or musical instruments that will be babied or on items like gears and bolts that will live their lives in an oil or grease environment. Yes 200 years ago it was a GREAT rust preventative but it was only great because people had nothing better!
With today's mad scientists we have all sorts of platings and polymers that have made blueing virtually obsolete. I do have to admit that I still do see blueing used in decorative environments but the way it is protected has also gone the way of the polymer revolution and for good reason.
The four things which destroy blueing are air, water, handling and acids. Air and water are hard to escape from. They are all around us at all times and they are in our bodies as well.
Oxygen of course is the real killer that is found in both of these things. In plain simple English oxygen combines with iron and makes rust. No chemical explanation needed here everyone of us has seen rust. The old methods of protecting blueing simply do not work that well. Oxygen has a tendency to work its way through both oil and wax if the parts are given enough time or are handled.
Handling blued parts has its own set of problems. Repeated handling strips the oil or wax away exposing the blueing and the acid in our hands eats blueing faster than you can imagine. People who are at the highest risk seam to be those who drink alcohol eat a lot of red meat or consume a lot of fruit.
The modern epoxy polymers seem to do a wonderful job of protecting blueing. They are tough, do not allow air, water or acids to pass through them and will stand up to very heavy handling and or use or misuse.
My best recommendation to you would be to send them to an automotive type paint shop and have them clear coat the parts with an epoxy. The shop will degrease the parts before they paint them and I have found that for what ever the reason there seams to be no need to prime the parts. One coat of clear coat should do it just fine.
I would be willing to bet just about anyone a case of beer that the parts have been caustic blued and not cold acid blued. Acid blueing is cheep if you are only doing a few dozen parts but because of the labor involved I doubt that any fool would try to acid blue 50,000 units.
If you just want to de-grease them and get them out of your hair which is what I expect you really want to do, just go out and buy a 50 gallon drum of Varsol or kerosene and slosh the parts around until the oil is gone. Put a light coat of paste floor wax on the parts with a paint brush, buff lightly with a rag, and pray you never have to bid on a job like that again!

A. Well as I have always understood it Varsol, is just ExxonMobil's version of mineral spirits ⇦ this on eBay or Amazon [affil links] or paint thinner, whatever you want to call it. Kerosene is what the aircraft industry calls Jet A. It's the fuel that commercial jet liners use to cart us all over the world. I guess for all intent and purpose it's also a mineral spirit. The parts will have to be protected with wax or oil after being washed in any of these solvents. If not, they will rust!

A. Hi Madi.

I think it unlikely that you will be satisfied with black oxide on furniture. At best it will be oily or smutty. Zinc-iron plating with a black chromate topcoat would be better, but the overall most satisfactory solution would doubtless be black chrome plating. Good luck.

Regards,

A. Hi Terry. Any local plating shop who does barrel plating probably has centrifugal dryers (like the spin cycle on your washing machine, but designed for metal parts). These will fling off the excess oil without removing it all and leaving the fasteners rust-prone. Good luck.

Regards,

A. Hi Jon. The 'black oxide' that we are talking about here, is the same finish, with a different name, as 'gun bluing', and fastidious hunters wipe down their guns with an oily cloth after every use. Consequently gun oil is one such product you could use, but general machine oil like 3-in-1 should be fine too. There probably are 'rust-preventative' oils designed for the purpose as well.

Luck & Regards,