How to Cold Blue (Blacken) Armour

by Matt Stitchman

Bluing is a controlled oxidization (rust) of the metal. It’s not going to work on stainless steel or other metals besides carbon steel for that reason. This thin layer of rust (which is a blue/black color thanks to chemicals in the bluing solution) and the fact that the oxidization is controlled forms a protective layer over the steel beneath it. Basically the rust on the outside keeps oxygen from getting at the steel on the inside and allowing it to rust.


Bluing Solutions
The brand does make a difference. The best I’ve used by far is Black Magic which you can get online from Kleen Bore. Hoppe’s is decent but not as forgiving, and Outback is not recommended for this purpose. Those are all the brands I’ve used, but others may be good too. (Editor’s note: other brands available are Super Blue and Perma Blue from Birchwood Casey, and 44/40 by Brownell’s.)

You want the strongest, meanest degreaser you can find. I used engine cleaner with good results. Basically go into your local auto parts store and ask someone at the desk what the most powerful degreaser is and get that.

I use sewing machine oil. Gun oil should work fine too but it’s more expensive. Any similar light machine oil should work fine. WD40 is not oil, it is a cleaner and can actually damage the blued finish.

Additionally, you will need:

A sponge
Some clean rags
A bucket that’s big enough for your pieces to fit into
Hot water (your hotwater tap will do fine)
Rubber gloves
Safety goggles
A well ventilated area
(see also: An Armourer’s Basic Safety Guidelines)


The first step is to put the finish you want on your project. The better the finish, the better the final results will be. A mirror finish before you blue will get you a blued mirror finish etc. Now before you begin you want to set everything up. Work in a well ventilated area (like outside), as these are very toxic chemicals. Degreaser is very toxic and bluing solution is mostly just acid.

Lay all your pieces out. Tear rags for cleaning degreaser off, drying the armour and oiling the armour. Keep these rags separate. Get your gloves and sponge ready and put on your safety glasses. If you’ve got one, a respirator is a very good idea. If you don’t have one you might want to consider getting one. Make sure there are no pets, children or other innocent bystanders around. Put the rubber gloves on. Don’t take them off until you’re finished.

Fill your bucket with hot water. Spray the aerosol degreaser generously over the entire surface of the pieces to be blued. Let it dry and then clean the degreaser off using the first rag. It is important that you do a good job cleaning it off. Now that your pieces have been degreased don’t touch them with anything but rubber gloves until they’re blued. If they are touched with human hands they’ll need to be degreased again.

Now open your bluing solution. Moisten a corner of your sponge with the solution. Don’t put a lot on. You want it to be wet but not wet enough that you’ll get liquid squeezing out and running down the armour.

Wipe the solution on the armour using unidirectional strokes which are as long as the piece is. The reaction will happen almost instantly. Once you’ve done the entire piece you’ll likely have some lighter blotches or streaks. Start at the side you started at and go over any areas that are lighter and repeatedly stroke over them until they match the rest.

Set the piece down and move onto the next. Don’t do too many pieces at once, as you don’t want to leave the active solution on for more than a half hour.

Next, starting with the first piece you blued, dip it into the hot water and gently swish it around a bit. Take it out and dry it with the second rag immediately.

Now here’s where brands come into play. If you’re using the Kleenbore product you won’t need to oil it right away, so you can dunk and dry the rest of your pieces. If you’re using Hoppe’s, however, you’ll need to oil the piece immediately after you dry it or you’ll get the kind of rust you don’t want.

Oil each piece by squirting a few drops onto the piece and then rubbing the oil around with the third rag. Make sure that the entire surface is covered in a fairly generous amount of oil. The oil is very important as it stabilizes the piece. You want more oil on the piece now then you would normally have on armour, since the oil will be partially absorbed. Once everything is oiled check your pieces for any spots where the oil has all been absorbed and the surface has become dry. Add more oil to those spots. Check again in about a half hour and again a half hour after that. Any spots that are left dry will rust.

By the next day the bluing should be completely stabilized and you can enjoy the rust resistance (not immunity) that bluing gives. You should still keep your armour oiled but the extent of the oiling only needs to be wiping your armour down with an oily rag after use or handling. It will be less prone to rusting then unblued armour but not completely immune.

As bluing is a surface treatment it will be prone to scratching. Be sure to keep any scratches oiled. You may periodically need to touch up the bluing if you’re getting scratched up often by fighting or other activities. To touch up the blueing just degrease, blue and then oil the scratched areas using the techniques above. It’s not necessary to remove the previous bluing.

Matt Stitchman runs Mad Matt’s Armory