Tuesday, March 10, 2020

Rust Bluing for the Home Hobbyist

What is Rust Bluing?
Steel rusts. Since our species has been making steel tools we've been searching for ways to stop that from happening. Bluing is the most common method of protecting steel from the elements. These methods include things such as:
  • Browning
  • Fire bluing
  • Cold chemical bluing
  • Hot caustic salt bluing
  • Rust bluing
Rust bluing results in a very durable finish. When done properly you will have a blued metal piece that is nicely polished. World famous British gun maker, Holland and Holland, still uses the rust bluing process today on their very high end firearms (When I say high end, I mean if you don't have 12K to spend on a double barreled shotgun, don't even walk in there)

The process, at its core, is pretty simple. You take metal, let it rust into red oxide, convert it to black oxide, stop the reaction, and then polish. However, the process is time consuming. You can refinish a pistol in a day, but it is what you will be doing all day.

What do I need to get started?
You are going to need a bunch of stuff to do this properly. Luckily it's all pretty cheap

Pre-Work Materials:
  • Sandpaper (300 - 600 grit)
  • Degreaser
  • Nitrile or latex gloves
  • Lint free cloth
  • Goggles, face shield, or other eye protection
Bluing Materials:
  • Large, but ideally shallow, pot. Unless you want to be sleeping on the couch, don't use the pots in the house. Go hit the thrift store and pick one up. I got mine for 4 bucks
  • Steel wool (000 or 0000)
  • Fine wire brass or steel brush. I prefer brass as it won't mar, since brass is softer than steel
  • More gloves
  • Goggles, face shield, or other eye protection
  • 1 gallon of *DISTILLED* water. This must be distilled water or your reaction is going to be ugly and you will not like the results.Other types of water are going to have minerals and other impurities in them.
  • Bottle of Mark Lee Express Blue #1
  • More lint free cloth
  • You will be working with an oxidizer, but you don't need to wear a respirator. That said, during the boiling process, avoid inhaling the steam as it's probably not good for you.
Finishing Materials:
  • Chemical resistant gloves. Those thick yellow rubber ones they sell with the cleaning supplies at the grocery store will work. You will be working with lye/caustic soda during this process. You need to protect yourself from chemical burns
  • Goggles, face shield, or other eye protection
  • Polishing wheel
  • Polishing compound. I prefer Flitz
  • 2 pounds of lye or Sodium Hydroxide. You'll be making up caustic soda to stop the reaction
  • Container to hold your caustic soda liquid. Get something that's unlikely to result in spills Label it so people know what's in it and that it's dangerous. I went with a 1.25 gallon HDPE gas can because it has a pour spout that is closed by default and a nice flat base so it's unlikely to tip over
  • 1 gallon of distilled water (yes another one)
  • Lint free cloth
Prep Work
Preparing the Part
For this to work right you need to put in some work ahead of the bluing process. This is where the bulk of the hard work comes in. The time you take to prep your part and the thoroughness with which you do it will directly determine the outcome of the final product. The four main enemies here are:
  • Pre-existing coatings
  • Existing rust
  • Pitting
  • Oils/grease, including the oils on your hands
First, glove up. From this point forward you will not be touching your parts with bare hands until we are done. The oils on your fingers will mess up the finish. Even if you can't see them, they'll be there. I have a part I blued years ago that looks great except for a thumb print that's clearly visible on the finish.

Second, you want to make sure the part is free of any existing coatings. If the part has previously been cold blued, you can remove that bluing by soaking the part in apple cider vinegar. If the part has been lacquered, as is the case with my axe head, you can get that finish off by soaking it in something like Brownell's Steel White. I soaked the axe head for 12 hours, then hit it with a wire wheel, then a steel brush, then sanding.

This axe head has a lacquer on it that will prevent bluing

The part after cleaning. Note the lack of a shine
Third, you want to make absolutely sure your finish is free of rust and pitting. You might be thinking, "Why do I have to get all the rust off? Aren't we going to be rusting these parts anyways?". Rust is like cancer. If you do not get it off before we start the bluing process it will survive under the finish. Even a little bit left in some pitting will grow under your nice finish and ultimately ruin your part. You can take a wire wheel or a Dremel to the part if it's in rough shape. From there hit it with with 300 grit sandpaper in a circular motion, then 400 grit, then 600 grit.You want a nice smooth finish free of rust and pitting.

Fourth, degrease the part. I use an industrial degreaser available at Harbor Freight that comes in concentrate form. I mix it up a bit stronger than the directions say. Once you have degreased, wipe your parts down with a lint free cloth and put them somewhere where they won't pick up debris.

Preparing the Caustic Soda
At the end of the bluing process we are going to need to kill the reaction. We do this by soaking the parts in "caustic soda". So, what the hell is caustic soda? Caustic soda is quite literally lye (sodium hydroxide) in an aqueous solution. You'll be using 1.5 pounds of lye to 1 gallon of distilled water.

Your caustic soda supplies. Not pictured: Gloves & eye protection

Fill a pot or tea kettle with distilled water. You don't need to fit the whole gallon in there. Get the water hot, but not boiling. You're just warming the water up to help dissolve the lye. While you are waiting for the water to get hot, dump your pound and a half of lye into your container and put on your personal protective equipment (PPE). Once the water is hot, pour it slowly into the container with the lye. BE ADVISED, you will most likely get a hot jet of caustic steam out of the container so make sure you are not holding your face over the opening. Have the windows open as well. Should you get a face full of caustic steam, get your face under cold water quickly and rinse for 10 minutes. Hopefully you were wearing your eye protection, but if not wash your eyes out for 10 minutes as well. Once the hot water has been added, add the last of your gallon to the container and seal it up. You want this solution to be roughly room temperature when you need it later (another good reason not to heat all of it up)

Clear your schedule, because you're now ready to start rust bluing

Rust Bluing
Congrats, you're about to start your first rust bluing project.

First, get that pot of distilled water boiling. Don't fill the pot all the way up. You want enough water to cover the part plus another inch or so. Filling the pot all the way up increases the chances of splashing and it makes it harder to get your parts out. Keep your jug of distilled water handy and just top up the water as you move through the process

Next prepare your work space. Think about where you will be working and where you need your tools. I keep my tongs near the pot of water along with paper towels to put my wet parts on. I keep my supply of gloves and rags next to that.

Since I'm doing this in my kitchen, I wrapped the cutting board in cling wrap, then laid down some paper towels. I don't want any of this nasty stuff getting on surfaces where I will prepare food. That said, I also scrub everything down when I'm done regardless

Pour some of the bluing solution in a container that you can easily dip your sponge in. Remember, a little goes a long way with this stuff. You don't need the sponge soaking in it. As you move into the next rounds after round 1, you'll mostly just be moistening the sponge again
I ultimately cut the top part of the cup off so I could get in there better

Throw your gloves and PPE on. Set your oven to 'warm' and put your parts in there so they can begin warming up.
Get in here Billy, granddad's making cookies!

Once your parts are about 100 degrees (F) you're ready to start with your first round of bluing. Take the parts out of the oven (be careful you don't burn yourself). Holding the part firmly, begin to apply the bluing solution with the sponge in nice, even, strokes. Also remember to work in 3 dimensions! Get the sides of the part, underneath, on top, any holes in the part. Also remember to blue the part you are holding as well. The reaction should start immediately. Should the reaction not start you might be dealing with 2 issues:

  • The part still has some kind of coating on it that needs to be removed
  • The part is aluminum or another non-steel material. You can't blue aluminum! You can anodize it, Duracoat it, Cerekote it, but you can't blue it.
Now that you've applied your first coat, set the part down and let it sit for 30 seconds. After 30 seconds, apply a second coat and let it sit for another 30 seconds. 

The process begins. Don't freak when your parts look like this initially

Now that you've added two coats of solution to your part(s) it's time to boil them. Carefully place the part in the boiling distilled water and set a timer for 5 minutes.

Mmm. That's good soup!

After 5 minutes, take your parts out of the bath and place them on the paper towels. Dry the parts with a clean towel. If there's any build up of material, hit it lightly with your brass brush to clear it off. Be careful, they will be hot. In fact, you'll be working with hot metal for the remainder of the day.

Once the parts are dry, take them to your bluing work space and begin the process anew. Once you've applied your bluing solution twice, drop the parts back in the boiling water and do this again. Overall, you will be doing this *eight* times.

Each time you do the cycle, you will notice more and more of the surface is turning a uniform color. Don't be concerned if they don't look dark after the first few rounds. This is an ongoing process.

For example, this is what the parts looked like after round 3:

Parts are darkening, but clearly have a ways to go

After round 4 I decided to make a quick video of the process:

I'm not very good at videos

And after round 7:

Parts are much darker and uniform in color now

And after round 8:

We're going to call this done!

Stopping the Reaction
We're almost done and you're about to get a break! We've repeated the coat/boil process 8 times and our parts are looking pretty darn good.

Take care when working with caustic soda it can burn you

Turn the stove off and carefully dump that nasty distilled water you've been boiling down the sink. Wash the pot with hot water (no soap) and wipe it down. Set your pot on a cold burner or the counter top. Place your parts in the pot. Now slowly and carefully pour your caustic soda solution over the parts till they are submerged.

You'll now be happy to know that the parts need to sit for 90 minutes. Take your gloves off, take off your goggles, go catch up on Facebook.

Clean up from this stage is a snap too. Once you've removed your parts simply pour the caustic soda down the drain. Sodium Hydroxide in water is basically Drain-o. You're doing your pipes a favor by pouring it down the sink. Just make sure you don't get it on you and clean up anywhere you might spill. After dumping it down the drain, I run hot water from the tap into the sink for a few minutes. Make the most of your pipe cleaning!

Final finishing and Wrap Up
Pat yourself on the back, you've prepped your parts, you've rust blued them, and now you've killed the reaction. The final step is to finish up the part to give it a nice finish and to protect the metal. You have two different routes you can take here:

*Don't forget to put your PPE back on*

Option 1: Polish the metal
Take your parts and apply your favorite polishing compound. I use Flitz because it is nonabrasive. I don't want to polish off the nice finish I just spent all this time putting on. I apply a nice coating of Flitz, let it sit for a few minutes, and then buff it off with a polishing wheel on my drill press

I then do it again. Once I've polished twice I wipe everything down with a nice, clean, rag and call it a day. In a few days I'll wipe my parts down with some sort of gun oil (I usually use RemOil) to further protect them.

Option 2: Oil impregnate the metal
This option takes longer and will result in a higher luster in your metal. If you're going for a matte finish, you're probably better off with option 1. To oil impregnate the metal you will need a couple of things:

  • Quart of motor oil (doesn't matter what kind. I use 10-W30 because its what I run in my car)
  • Cling wrap or a container that can hold the parts
Put your parts back in the oven on warm. Once the parts are nice and warm either place them in the container you set out and cover them in motor oil or coat them in a thick layer of motor oil and wrap them in cling wrap. Let those parts sit for the next 24 hours. Once you let 24 hours go by, take your parts, wipe them down, then polish them up on your polishing wheel

I went with Option 1 for my parts because I wanted a nice matte finish. Don't be surprised if the finish changes a bit when you look at your parts the next day. Mine went from a deep black to a black/grey that looks really nice

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