4 months by cncdivi

What is Cold Bluing and Black Oxide for Steel?

Bluing and Black Oxides are essentially the same thing.  Older methods required that parts be submerged in vats of dangerous boiling chemicals.  With Cold Bluing and Black Oxide, the chemicals are much milder and no heat is required.  Pretty cool, eh?

You can blacken a number of materials including ferrous materials, stainless steel, copper, copper alloys, zinc, powdered metals, and silver solder.  The exact materials yo can blacken will be based on the recommendations of the makers of the particular chemicals or kit you use.

The art of bluing steel has been used with firearms since the very beginning, but bluing is much older than firearms.  At first a thin coating of oil was used to prevent corrosion in iron and steel, but eventually bluing processes were invented to provide much better protection.  Some of the oldest examples appear in ancient Japanese swords.

Why Cold Blue or Black Oxide Coat Steel?

Okay, so why bother coating steel with Cold Bluing or Black Oxide?

In a word: Rust.  These coatings are there to deter rust.

The chemicals associated with these treatments convert a surface layer of the steel to magnetite.

How Does it Compare to the Older Hot Methods?

Cold Black Oxide is not an oxide conversion coating.  It is a deposited copper selenium compound.  Hot Black Oxide  involves hot baths of sodium hydroxide (the nasty stuff in drain cleaner), nitrates, and nitrites.  Hot Black Oxide converts the surface into Magnetite.

The Cold processes produce a similar color, but the coating tends to rub off more easily and offer less abrasion resistance.  The application of oil, wax, or lacquer will bring the corrosion resistance up to par with the heated processes.

If you need the additional protection, most shops will send parts out for Hot Bluing rather than deal with the mess in the shop.  For small batches and the DIY’er, the cold processes are much easier to deal with.

Quick and Easy Cold Bluing and Black Oxide Kits

Cold bluing uses acids to put an oxidized finish on steel at room temperatures, or close to it. They’re very easy to apply, requiring only a thorough degreasing before application. For fun I compared the finish from two Brownell’s cold bluing products:

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Dicropan T-4 and Oxpho-Blue Creme Cold Bluing Test

Both the Dicropan T-4 and the Oxpho-Blue Creme came as creams, which made them easier to apply. To perform the test, I took the spacers I had made for my new 6-jaw chuck backplate and compared the results. I simply cleaned them in some mineral spirits and then applied the compounds with a folded paper towel.

Do this wearing gloves as the chemicals are fairly nasty. The steel turns blue quickly, after which you rinse it in cold water to remove and neutralize the chemicals. I then oiled the parts with Break Free, which is also an excellent anti-corrosive. The oil helps bring out the blue a bit more.

My conclusion was that the Dicropan looked darker, almost black, and seemed to go on more evenly. On the other hand, the Oxpho-Blue showed more blues and was a prettier finish despite it being less even. If you want to try Dicropan, it’s just $18.95 on Amazon.

Rear three: Oxpho-Blue. Front spacer: Dicropan T-4.

Commercial Grade Black Oxide

For shops that want to do Cold Bluing in volume, the little kits for DIY Gunsmiths are prohibitively expensive.  Check out what’s available from firms like Birchwood to see the more professional solutions.


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