What is the "Blackodising Process"

A. No. The finish is a few millionths of an inch thick and offers no hardness or abrasion resistance (and very little corrosion resistance).

Luck & Regards,

A. Hi, Rakesh. Although I haven't heard the term 'blackodising' used in my country, from numerous letters posted to the site it is apparent that what American metal finishers call "black oxiding" is often called 'blackodising' by metal finishers in India.

It's an oxidation process (most people have seen it on rifle & shotgun barrels) and is done by immersing steel in a very hot (290 ° F) solution of strong caustic soda [affil links] , plus oxidizers like nitrates, that leaves the steel with an extremely thin but attractive blue-black color. It is always oiled or waxed and offers negligible corrosion resistance without the oil, and little protection with it. We have a brief "Black Oxide vs. Cold Blackening FAQ" on line here. You can read a good introduction to the process in the Metal Finishing Guidebook. Good luck.

Regards,

A. Hi, Vaibhav. Blackodising offers little corrosion protection -- none without oil. The matte vs. shiny appearance of blackodising depends on how matte or polished the substrate was though. A very highly polished surface comes out more dark blue than black.

Dull nickel plating might possibly do for you. But certainly it is possible to apply a corrosion resistant plating sequence that ends with matte black chrome if that's what you want. Good luck.

Regards,

A. Hi, Mr. Mani.

You will definitely want to use proprietary chemicals, whether hot or cold, because you are new to blackening. Please contact any local supplier of plating process chemistry and they will be able to help you choose whether hot or cold is better for you.

adv.
- Cold blackening is a major product line for EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser]

Good luck.

Regards,

A. Hi Ravi.

Blackodizing is explained on this page. "Blackening process" doesn't really have any specific meaning, any more than "whitening process" or "brightening process". Blackodizing is one blackening process, but it's easy to imagine others.

Regards,

A. Hi Mahesh. Certainly zinc plating can be done... it's the world's most popular plating service. And it can be black if you wish.

But you haven't yet given any indication of what you are black oxiding or why, so people can't guess whether zinc plating will prove okay. Please get back to us with the details of your situation and people can try to help you. Thanks.

Regards,

A. Hi Abhijeet. Please read our FAQ, and then the Metal Finishing Guidebook, and meet with a local distributor of blackodizing chemicals as we've suggested. If that effort leaves you with some highly specific questions, please post them and people will probably be pleased to try to help answer them.

But different steels require different processes and temperatures, and different precleaning, and you need to decide between hot and cold processing, and waxing or oiling, depending on what kind of parts you intend to produce for who and why. And the safety issues of hot black oxiding are very serious. Sorry, but we can't condense the subject of how to specify, design, build and operate a blackodizing plant into a forum response here :-)

After you have read some good introductions, please get back to us with specific questions. Thanks!

Regards,

A. Hi Surya. As you say, the corrosion resistance of blackodizing is very little and depends mostly upon periodic application of oils or waxes. The advantages of the finish are its appearance, and the fact that it causes no dimensional change (whereas painting and plating have measurable thickness). It's a finish that is best restricted to items that are lovingly maintained (like firearms), or where dimensional changes aren't acceptable (like bored gears and sprockets), or where there are no corrosion issues (like indoor use in controlled atmospheres).

Regards,

A. Hi Sumit. Please begin by reading our FAQ on the subject and then the relevant chapter in the Metal Finishing Guidebook as we've asked twice on this page already. Then you might wish to review letter 1150, "The black oxide process and gun bluing" where Rod Henrickson answers all your questions about chemistry and operating conditions. Then do a search of this site and read additional threads about black oxiding.

But if you do not have access to a knowledgable black oxide consultant, or at least an experienced gunsmith, we must again urge you to go to a proprietary supplier of black oxide chemicals and equipment, as it is quite a stretch to go from even rather good book knowledge to designing, installing, and safely operating a practical black oxiding process. Best of luck.

Regards,

Hi cousin Bhushan. As a student, you may want to practice the synthesis of knowledge acquisition by gathering facts from here and there, and merging the bits & pieces into a fuller picture. Do you understand why objects may require finishing of some sort? Do you understand that every process has advantages and disadvantages compared to other processes? Do you understand that blackodizing is one of those many potential finishes?

If so, then previous statements on this page beginning with "leaves the steel with an extremely thin but attractive black color", "always oiled or waxed", "offers negligible corrosion resistance without the oil, and little protection with it", "matte or shiny appearance", "the safety issues of hot black oxiding are very serious", "It's evident that this process does not provide corrosion resistance", "advantages of the finish are its appearance, and the fact that it causes no dimensional change" should provide plenty of fodder for your essay.

Please prepare and then post a two or three-paragraph abstract and we'll be happy to review it. Good luck.

Regards,

A. Hi Vinod. When parts are black oxided, it is not a matter of just dipping them into a single tank, but taking them through a process sequence of cleaning, rinsing, activating, rinsing, oxiding, rinsing, boil-out and post-treatment with wax or oil. So, when you ask whether black oxiding involves a dip in rust preventative oil, or whether it's a separate process, it's a question of semantics, i.e., whether you are referring to the black oxide tank proper or the usual black oxiding sequence.

In any case, even with a dip in good rust-preventative oil, the corrosion resistance will only last as long as the oil. If shipping overseas, you must keep the environment away from the parts. The parts must be literally drowning in oil that keeps the salt air away, or they must be sealed away from it.

Regards,

A. Hi Yogesh. The root cause is that your process does not produce parts with sufficient corrosion resistance to resist salt spray for 24 hours :-)
What are the parts made of, and what is the process sequence (including the lacquer, wax, or oil) that you are employing? Please don't expect black oxided parts to resist 24 hours of salt spray without an effective lacquer, wax, or oil post-treatment! You're lucky when they can resist the ambient environment for a 1/2 hour without flash rusting :-)

Regards,

A. Hi Manoj. Castings and MS are entirely different metals (for example, lots of silicon in castings), so it's to be expected that they won't automatically adopt the identical look when oxidized. I don't know enough about black oxiding to answer your question well ... because what you probably would really like to know is what to do to get them to look more like each other. But I think the first step is an equal degree of polishing. Hopefully an experienced black oxidizer will jump in and help :-)

Regards,

A. Hi Sachin. If I understand your situation, you gas nitrided some parts but you are unhappy with their patchy appearance in the ground area so you want to black oxide them. Although I have no personal experience with it, my understanding is that this can work, i.e., that you can blackodize nitrided metal without harming it ...

However, the black oxide is millionths of an inch thick, and not hard, and will quickly wear off. You might consider the QPQ salt bath nitriding process instead. Good luck.

Regards,

A. Hi Eshwar. Although some modifications to the black oxide process can generate a brownish color, I wouldn't rely on visual determination of a finish even looking at the actual parts rather than a photo; and I doubt that black oxide would prove satisfactory for this duty anyway unless the spurs are strictly decorative.

But if you wish to make spurs which look rather like these, and assuming they are made of steel or iron, I'd suggest looking into electrocoating with a brown post dye. If they are actually made of aluminum they can probably be anodized. Please tell us your situation; as things stand, we can't post responses to this particular question from people not known to us for fear of crowd-sourcing industrial espionage :-(

Good luck & Regards,

Hi Nitin. The chemicals used are indeed 'hazardous'. More importantly, the process is hazardous because it is an aqueous process which operates far above the boiling point of water and is thus subject to 'erupting' if make-up water flashes to steam because of improper addition methods.

The process could be "banned" in certain areas of the world by local, regional, or national governments, but I doubt that it is banned in your area.

Regards,

A. Hi Krishna. I've already expressed my opinion twice on this page that they are the same thing -- usually called black oxide in the USA and usually called blackodizing in India. Other people are welcome to offer their take on the question. But the problem will remain that both terms are slang more than specification. So if you simply specify blackodizing there is at least some chance that you'll get cold blackening rather than hot black oxide, and be into a contract dispute.

Luck & Regards,