Wikipedia has a lovely article on steel bluing. I use a process they term cold bluing, because it requires no heat, but is also called chemical bluing. Read that if you're interested in how this works. I am not a chemist. It should be noted that this process only works on steel, so those of you with aluminum are on your own.
Materials
Materials you will need for this process:
- Abrasives (i.e. sandpaper, sanding sponges, etc.)
- Clean rags
- Painters or masking tape
- Protective gloves - the rubber/nitrile kind, not the woodwork shop kind
- Degreaser
- Chemical bluing agent (sometimes called gun blue)
- Cotton balls
- Black shoe polish
- Protective sealant (I favor gun oil, and it comes in wipes)
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| Some of the materials needed |
Rust Removal
I’m going to assume you have a rusty piece of gear to start with. Use your favorite abrasives to remove as much rust as you can. This is the most time consuming part. My gorget has been bad enough that I needed to start all the way with a wire wheel a couple of times before progressing to sandpaper. Move through progressively finer abrasives until you get to the finish you want (a dream) or you’ve reached your point of patience (depends on the amount of time I have on my hands); 220 grit is a good finish, 320 is better. Some people use a lubricant while you’re doing this; it will be your bane later if you do, so leave it out this time. Once you’ve got as much rust off as you can, wipe down your object with a clean rag to get off all the dust you’ve created.
Mask
If there are any parts of your object you don’t want blued, now is the time to cover it with something. My gorget has a lovely stripe around the outside edge, so I usually try to very carefully cover it in painters tape so I don’t have to worry about the chemical bluing accidentally hitting it, and having to clean it up later. This last time I cheated and didn’t do it, so to each their own.
Degrease
Now it’s time for the gloves. You are about to start using chemicals, some of which are caustic to humans, so these are important. I have a pair of longer kitchen-type rubber gloves that come out only for this process (but they’re black, so it’s cool). Nitrile/latex gloves might also work fine. Spray your object with degreaser, and wipe down with another clean rag. You’re looking to get all the oil from your hands off of the object so the bluing will work well, as well as any remaining dirt or grime. Wait for the object to dry - it shouldn’t take too long, especially if you place it in the sun. Leave your gloves on (dry them off if you got degreaser on them).
Blue
Now on to the fun part. You might want to lay down some newspaper or cardboard to protect whatever ground you’re over. Grab a cotton ball, get some bluing agent on it, and go to town on your object. Be liberal, but try to get consistent coverage, and don’t rush. The results will be almost immediate turning the metal a lovely bluish black, but it will probably look splotchy. You will likely need to go through many cotton balls as they’re not much use after the first go round. After a short while, a sort of yellowish scum will form on the object where you’ve put the chemical; this is a normal byproduct of the chemical reaction, and we’ll deal with it later. Any spots that look particularly splotchy should get a second coat (and you might want to just do a second coat all over anyway).
Finish
Once you are done bluing, find yourself yet another clean rag and start buffing the yellow scum off - it should rub off with a little elbow grease. You will have an object that is darker, probably a bit splotchy, and kinda dull looking. Apply black shoe polish liberally, and buff it to a shine (you’ve shined a shoe before, right?). The shoe polish helps even out the bluing and applies a nice wax coating to that section. Remove any masking you have done, and your object will be complete. For the masked portions, apply your favorite protective substance be it a wax or oil - my penchant is for gun oil, as it’s designed to seal out water and comes in handy wipes :).
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| Gorget & 2 guards that have been chemical blued |
