Rust Bluing: DIY Tips and Techniques

Before the advent of modern production methods, firearms manufacturers did things “the old-fashioned way.” Whether some of these older methods are actually better could be argued without either side changing their thoughts on the subject.

In any case, bluing, as done in the good old days, was essentially a hand-applied process that took time to accomplish. The end result of the express rust-bluing process I’ll describe here looks and wears just as well or better than some of the methods used in days gone by. In fact, it may even wear better than a few of the so-called “modern bluing methods” used on today’s production firearms.

Preparing the Surface of Your Firearm

Express or rust bluing is one of those tasks that, if begun properly, will almost always end up looking right. How the surface metal is prepared and handled during the application of the bluing formula is the real key to the end result. For the most part, mirror-bright finishes have gone away for a couple of reasons. Light reflection off a mirror-polished firearm can spook game animals during hunting applications. A highly polished surface is also too slick to hold protective oil, because all the pores in the metal’s surface have been closed up. As a result, matte finishes are often preferred these days, and this preparation is much easier to apply.

The first step when dealing with metal previously blued is to remove what finish remains. There are several rust and bluing removers available in liquid and gel form that work well enough for this phase of preparation. After the old bluing has been removed, a hot, soapy, water bath will remove what’s left of the remover solution. Look the metal surface over thoroughly for any pits or rough spots that will need to be removed. Small pits or nicks will require some amount of draw filing; just be cautious around screw holes and lettering like serial numbers and such. Try your best to maintain flat areas, curves, and contours that contribute to cosmetic appearance.

When you are completely satisfied that the file is no longer necessary, 220-grit emery paper is the next step to help remove the marks from draw filing. Strive to keep the sanding parallel with the bore line, and always back your emery paper with a flat block or wood dowel sized to match the contour you are dealing with. I realize that sanding with the bore line is not always possible, but if you can do this in the larger areas there will be less blending to do later on.

Work progressively from 220 grit to 320, and then to 400-grit paper. If you desire a finer finish, then move up to 600, then 800, and finish with 1200 grit. Brownells has all these emery papers available in their catalog. If you prefer to go with a soft matte-type finish, consider the various grades of Scotch-brite blending pads they sell, and switch to those after the 400-grit emery-paper finish. If the metal is badly pitted, consider a medium grit sandblast to texture the surface. Sandblasting can help disguise some very ugly areas before the bluing is applied.

Cleaning Your Weapon Completely

Once the metal surface has the desired texture or finish applied, it’s imperative that all oils and fingerprints are removed. Clean the metal thoroughly with acetone or lacquer thinner. Wear rubber gloves and work in a well-ventilated area. Don’t touch the metal surface with your bare hands after this phase has been completed. Once the parts are clean, cotton jersey gloves will help to keep skin oils off the parts and still give enough dexterity that you can handle all the gun parts that need to be handled.

Because the bluing solution used here is acidic, it somewhat etches the metal surface. Therefore, we need to protect the bore to prevent any of that type of action happening in there. I use shellac or varnish to coat the inside of the barrel and protect the rifling from the rust bluing process. I usually apply two coats with a bore mop, with one coat applied from the chamber end and the other from the muzzle end. Let the varnish dry thoroughly and then remove any that has dripped or run onto surfaces you intend to blue. Varnish can be removed with a soft cloth dabbed in a small amount of acetone. Once the bluing job has been completed, the varnish is easily removed from the bore with a brass bore brush and acetone.

Prepare a Work Area for Bluing

The best way to start is to prepare your work area with all the tools you’ll need to get this job finished without too many interruptions. I lay out newspaper on my bench top with a juice glass filled about one-quarter full with bluing solution. Shake up the plastic bottle of solution real well before you pour some into your working container. Cotton balls and two-inch square pieces of old white T-shirts work well to swab on the solution. Paper towels are also handy to have at hand when doing this type of bluing. I use Bounty brand paper towels only because they really do absorb better than some of the stiffer paper types.

You’ll need a metal tank large enough to hold the longest barreled action you anticipate bluing. Don’t scrimp here, buy yourself a good sturdy tank. It pays to have an old kettle or pan handy to do handguns or small parts when not doing a complete rifle or shotgun. There’s no sense firing up your large tank for small jobs.

I now use only distilled water in my tank for boiling parts during this process. I’ve tried rain water, melted snow, and captured water from a dehumidifier. The best results are achieved when using distilled water. It seems there’s always some foreign stuff in the free water I’ve tried that will leave a blotch or spot that can be very tough to remove. I fill the tank with enough water to completely submerge the parts I’m bluing and then add a bit more, but not so much that the water boils over and makes a mess. Three-quarters full has proven to be plenty.

A source of heat to get the tank of water boiling mildly should also be close by your work area. Out here in the boondocks, our heat is supplied by propane. It was a simple matter to have the delivery person hook up a supply valve and shut-off in my shop. Don’t even think about using one of those portable propane tanks from your gas grill, it’s way too dangerous unless you are willing to work outside. If you have natural gas supplied, get with someone who can safely hook you up to that source. Or, if you have an understanding wife, ask her if you can use the stove and kitchen table. (Good luck with that endeavor.)

How to Blue a Gun

I’ve been using Mark Lee’s Express Blue, available through Brownells, for almost 15 years now, and I’ve found it to be the easiest to use of the rust blues I’ve tried. The first time I tried this bluing formula I had a successful result, and it’s been that way ever since. It works great on chrome-moly barrels, blackpowder barrels, and best of all on those older double-barreled shotguns that are soft-soldered together at the joining rib.

In use, the metal to be blued is heated to around 150 to 170 degrees before the application of the solution. I wouldn’t recommend a propane torch as a heat source, because it’s impossible to tell whether the metal surface is at 150 degrees or 350 degrees. With a calibrated heat-gun that’s equipped with an indicator, you can tell when the metal reaches very close to the required temperature. I use a heat-gun that has a variable range dial on it. I aim the heat output end at a thermometer stem and turn the variable dial until the thermometer dial steadies at 150 to 160 degrees.

Now is the time to put on your cotton gloves, and don’t touch the metal with bare fingers during any of the next steps. Clamp one end of the barreled action in your padded vise so you have most of the metal hanging out in space. With the protruding metal heated as close as you can get it to the proper temperature, wipe the bluing solution onto the metal surface. You’ll see the metal almost instantly turn a rusty, reddish-brown color. Rotate and then clamp the barreled action in a different spot, apply the heat-gun to the metal in the new area, and then wipe the solution on once again.

When you dunk the swab in the bluing solution, squeeze the swab so that it doesn’t drip with solution. You just want the swab to be a bit more than damp. Yes, the solution will get all over the fingers of your gloves, but what the heck; the gloves can help apply the solution also. Keep rotating the barreled action in the vise and apply heat to the new area and wipe on the solution until the whole surface looks rusty brown. Let the solution work for 10 to 15 minutes and then apply another complete coat of solution in the same manner. The first two applications are best done one after the other. After the second application of solution it’s time for the distilled water bath.

Boiling and Carding the Gun Parts

While you’re applying the bluing solution it’s a good time to get your distilled water to the boiling point. When the water is hot enough to cause some slight bubbling on the surface, it’s ready to receive your solution-coated parts. I hang small parts from short lengths of coat-hanger wire into the hot-water bath. The coat-hangers span the top of the open tank with drop wires that in turn hold the small parts under the boiling water. This is much easier than trying to fish the small parts out of the hot water.

I don’t use wooden plugs in the chamber end, although I do use a wooden bore plug on rifle barrels. This dowel is a handy attachment for the suspending wire. I don’t plug the bore from both ends because I don’t relish the thought of being scalded by hot water should pressure build up in the bore and blow a plug out.

After about 10-15 minutes of boiling, the parts are removed. They’ll be coated with a velvety, black-oxide finish. The water needs to be poured out of the tank. Dry the parts off with paper towels in the areas where the water didn’t dissipate from the heat the metal is retaining. Let the parts cool until they are cool enough to pick up, and make sure you still have your cotton gloves on.

Carding is the process of removing the black-oxide surface finish. I use a hand carding brush specifically designed for this purpose. This is a fine wire brush with a wood handle that does quite a good job. At one time I thought this brush didn’t work quite fast enough so I scrounged up an old washing machine motor and set it up with a belt-and-pulley system that rotates the driven pulley at 200 to 250 rpm. If this kind of a setup interests you, here’s how I set mine up: There’s usually a tag somewhere on the motor indicating the speed at which the motor turns. We need to determine the size of the driven pulley to achieve a brush rotation speed of 200-250 rpm. If the motor turns at 1350 rpm, a one-inch pulley mounted on the motor shaft will also turn 1350 rpm. The diameter of the driven belt pulley that will drive the shaft that turns the brush will need to be determined. Multiply the diameter of the driving pulley (1.00-inch) by the speed of the rotating motor shaft (1350 rpm) and then divide this number by the rpm you want to obtain (200 rpm). In this case, we come up with a pulley diameter of 6-3/4 inches. A 6-inch-diameter pulley is more easily obtainable, and will give us 225 rpm for the brush. The brush rotates at a relatively slow speed, but you still need to be cautious while wearing those cotton gloves that you don’t get tangled up in the brush.

During the carding process we are removing a fine black-oxide dust so wear a respirator of some sort. The dust will irritate your lungs something fierce.

Once again, heat up the metal and apply another coating of solution on all the metal you want blued, and after the boiling process, card off the black oxide. You will begin to see the metal go from a gray color to a progressively blacker color. This can take from six to nine applications of heat and solution, the hot water bath, and then the carding process.

Rust Bluing Conclusions

Once the metal has reached the blackest color you can achieve, you need to seal the bluing and arrest any further oxidation. After the final carding, I rub all the metal down with a flannel pad. This will remove any residual black dust left on the metal surface from the carding process. All of the blued surfaces are then coated with RIG. This is a thin brown grease that is brushed over the blued surface with a 3/4-inch wide acid brush and then left on to allow the bluing to cure for 48-hours.

After this curing period, the RIG is removed with an old cloth and the bore is cleaned with a copper/brass bore brush dipped in acetone to remove the varnish that was protecting the bore’s lands and grooves.

Yes, this process is somewhat involved and will take an uninterrupted afternoon to accomplish. But the results are worth the effort, and are equal to or better than many of the other bluing processes.