Materials:

Aquafortis / Slow brown reagent
CLEAN cotton rags. (paint stores sell clean white "T-shirt" rags cheap)
Glass containers with tight fitting metal lids.
Racks, screens, wires, for suspending parts.
Acetone, a quart is about $6.00, a gallon is about $8.00. Get a gallon. It's useful stuff.
Clean newspaper.
LATEX rubber gloves. (I get 50 pack "surgical gloves" at the local home improvement/paint center).
Cotton swabs (Q Tips)
Soap/water/laundry tray or other wash up area.
Place to work, lay out parts for about ten days.

Aquafortis is the traditional name of nitric acid dilute which is used to finish both steel and wood on old guns.

Tru-Brown and Tru-Blue are brand names, basically nitric and hydrochloric acid dilute. Ol' Thunder Cold Brown, Laurel Mountain Forge Slow Rust Brown are other brand names for slow rust brown.

Birch Casey Plum Brown is NOT a slow rust process. Parts need to be heated. I've not used it. I like slow rust brown, more authentic.

Laurel Mt. Forge has a built in degreaser, but it's tricky to apply because it tends to "copper" the metal if you rub it. Also, last time I checked it was about $12.00 for two oz. --enough to do about two or three guns. It does a nice job if you don't run into coppering problems. I've had the parts copper when I applied the stuff with a daub of a cotton swab and no rubbing whatever. It's tricky stuff but a good product.

You need acetone, Formula 409 is good stuff to have too. LATEX rubber gloves -- I buy 50 packs of disposable "surgical" gloves. DON'T get the plastic/vinyl/nitril gloves, acetone and acid will disolve them. I'm betting that Playtex dishwashing gloves are vinyl and nitril. I have a pair of heavy duty latex gloves, but they're too heavy for decent control on small parts. Get the gloves, acetone at the local Home Depot etc.

You need to polish the parts. I use steel wool and a wire wheel on a bench grinder. I go to 0000 steel wool, but if your parts have been blued, they're already finished smooth. Ultra smooth finishes are difficult to rust. You don't need the "mirror bright" finish required for bluing.

I use Birch-Casey rust/blue remover. This stuff is noxious, be sure to get in a well ventilated area. I work in the garage/shop. Follow directions on the bottle, basically rub on, let sit and buff off with steel wool or wire wheel/brush.

You need a room with decently high humidity. The bathroom works, but it gets tied up for ten days or so. If you're single you can swing this fine. A family will raise hell with this part of the process. You need an area where things are not going to get touched. Any work room will work except a sauna which is high heat and no humidity. I'd stay off the rugs and the dining room table. You're working with acids and solvents.

Plug your barrel with hardwood plugs. I tap these in with a mallet. If you're hanging your barrel from a wire during this process, you want the plug tapped in tightly so it won't pull loose. On a breech loader, you want the breech plug inside the breech so that you can brown/blue the bolt housing area around the breech. You need to be able to get to these areas with swabs, and a stiff cloth. You can tap the breech plug out from the muzzle later. Leave enough of the muzzle plug that you can get at it with a vise or vise grips. I find that I need to put the plug in a vise and twist the barrel to remove the plug.

Degrease. This is a tricky process. Formula 409 will degrease the parts. Hot soap and water. The tricky part is isolating the degreased parts from your greasy environment. Clean newspaper works, clean gloves. Don't handle the outside of the gloves with your bare hands once they're degreased. Wash your hands with soap and water to remove the oils before working with any of these materials. Have your other chemicals laid out and degease the lids, containers, racks, etc. Needs to be clean and organized. Don't work if you're rushed. Try to have ample, clear space to work in.

Lay your washed parts out on newspaper . . . in an area you can leave for about ten days or more. Put on your gloves and wash the outsides with soap/water, rinse thoroughly. Wash the handles on the faucets to remove the grease/oil.

Further degrease with acetone. Acetone removes soap film and 409 residue. Acetone will get you high if you breath it. Probably kills off brain cells. It's a heavy duty evaporant. Don't leave it in an open container or on a rag that's laid out. Acetone is major league flammable too! Clean cotton rags, soak one in acetone and wipe down several GLASS jars with lids, inside and out. I keep my acetone rag in a jar with a tight lid. Plastic lids will disolve in acetone, use tight fitting metal lids.

Degrease parts and lay out on clean newspaper. Parts like barrels, bolts, barrel rings, I attach a wire (degreased) and hang from a clothesline (but I have a laundry room to work in). You want to keep the parts from sitting on a surface like newspaper. They need to be exposed to the air and covered with brown/acid. Newspaper soaks up the acid/brown and prevents free air circulation.

Smaller parts get laid out on a metal cake rack (degreased). The really tiny parts . . . screws etc. get laid out in a flour strainer -- stainless steel these days and only about two bucks at the local store. I put small parts in a jar with a little acetone to degrease, put on a lid and swirl. Then I pour the contents through the strainer draining the acetone into a second jar--the one with the "acetone rag." Put a lid on these jars, otherwise you get overwhelmed with fumes. You can press the mesh of the strainer on a flat surface and flatten the bottom so that parts can be left spread out on the mesh. The frame of these strainers is plastic. Acetone will disolve it. Get a stainer specifically for this purpose, it's no good for food afterwards. Keep the acetone off the plastic, but don't worry about it. Acetone mars plastic, but it won't melt it down.

OK, parts are buffed up to a good shine and degreased. Preparation is what bluing and browning are all about. Take your time in prep. It will pay off in the final results. Factory finish blue is a rust/oxidation process, so a bit of blue on parts that you're going to refinish in brown should not create problems. (I don't know this for a fact, but it makes sense.) Brown rust finish takes a less rigorous surface prep than rust blue. You need smooth surfaces with the finish lines running in on direction. But you don't need the "mirror bright" finish required of blue finishing.

Wipe the brown/acid on the parts. You want a smooth, even, damp coat. Cover thoroughly. Try to avoid bubbles, foam, and drips, but don't worry too much about it. Small areas get dabbed with a cotton swab. Just get the parts damp. This is where Laurel Mt. Forge gets tricky. If you rub it on, it "coppers." I like the other products because you can rub them on, go back over spots, touch up, without problems.

Let sit for about 12 hrs. Laurel Mt. Forge says six hrs. Some of the others say 10 hrs. Laurel Mt. Forge needs to be done in about 6 hrs. The other stuff gets done twice a day . . . about 12 hrs apart, but don't get anal about the timing. You can do the process every three hours if need be, but that's keeping pretty busy.

Wash your gloves/hands in hot water to remove the acids. Then pull the glove off inside out -- this is an Army Medic trick: grab the OUTSIDE cuff of the first glove with the fingers of the other gloved hand and pull off. Then, grab the INSIDE of the cuff of the second glove with the bare hand and pull off. Leave the gloves on clean newspaper inside out. I mark my gloves L and R on the OUTSIDE back so I can tell which side is covered in acid. When I'm ready to use them again, I turn them right side out, and blow in the cuffs to inflate fingers. Corn starch bath/baby powder -- they don't use talcum any more -- inside the gloves or on your hands will help get them on again. If you get your gloves turned inside out with the acid on the inside, you'll get a rash on your hands. Not life threatening, but a bit like poison oak. Pays to wash up and keep the gloves marked on the outside L and R.

When you're done handing parts and gloves, wash your hands with soap and water. You're handling acids and solvent, and you don't want them in your food supply or on your skin!

Once I get the parts degreased and a couple coats into the process, I toss the gloves and use a new pair. Wash the outside with hot water before touching your parts. (You DO want to get anal about the degrease thing.)

Your first couple of coats will freak you out. It will be blotchy, patches of rusty scale, black spots, runs, streaks, bald spots. That's just fine. "Card" the rust scale. I use a clean old toothbrush for tight spots and small parts. I use a patch of denim from old blue jeans. Make sure it's clean and free of grease. Drill cloth works. I'd stay away from polyester-acetone melts polyester. Some use 0000 steel wool. Steel wool is oiled. You can boil it for about ten minutes, wash in hot soap and water, and then soak in acetone to degrease. Of course you don't want to handle the oiled steel wool with your gloves, and you don't want to handle the degreased wool / acetone with your bare hands.

Carding scale is a matter of getting the loose rust off the part. A light rub with denim works fine. Steel wool comes apart and will remove all the finish if you rub too hard. With denim, you can rub stubborn spots to death without any problems. Rinse the parts and the denim patch/steel wool in hot water. The smoother you card the oxide, the smoother will be your final finish. I prefer the matte finish brown which is easier to achieve then the "glossy plum." Some browning reagents are more "aggressive" than others. This is a function of acid dilution. More aggressive reagents produce a more matte finish. Nonetheless, smooth metal is going to brown up as smooth metal -- similar to a Parkerized surface.

Degrease the parts again. You know the drill. Scrub the bare patches thoroughly. These probably have grease or residue on them.

Lay on more acid/brown. Rub firmly on the bald areas and then get them damp. Set aside for another 12 hrs. If you need to interupt this process just lay the degreased parts aside and do the acid coat when you next have time. But going even 24 hours on one coat of acid/brown shouldn't create any problems.

This process works best in a humid environment. The bathroom works, or a laundry room. I hang my parts over a laundry tub and fill it with hot water. This steams up the room. Small parts I put in the flour stainer and set that over a plastic tub (1/2 gal. yogurt container) with a wet rag in the bottom. Then I cover the strainer/tub with another rag to keep in the humidity. Medium sized parts that I can't hang are placed on a cake rack in a dish pan/tub. I put water or a wet rag in the bottom of the tub. You can cover this, but it's not necessary unless you're in a low humidity area. Humidity in Oregon is running 80% these days anyway so it's not a problem. Arizona may need some work to get the humidity up. Warm humid works faster than cold humid, but they both work. My gun shop friend hangs parts in his shower, runs hot water in the tub and closes the door. He has two bathrooms and a very cool wife.

You can build a "sweat box" . . . a tight box with a damp cloth in the bottom and a light bulb for heat. Be sure you don't set fire to the box with the bulb!

In about three/four days, the brown should start looking even -- maybe a few bald spots. Just keep at the process. Once the parts start to brown/rust things get easy. Keep applying coats until you get the deep, plum brown color. Check your final work in open sunlight.

The process takes ten days or thereabouts. When you get the color you're after, stop the acid process with soap/water. I use bicarb of soda (Arm & Hammer Baking Soda) in water to neutralize the acid. Sal Soda will work too. To blacken the parts--IF you want them black--boil for about five/ten minutes. Once blacked, there's no getting them brown again. I have yet to figure how to boil a barrel. The local gun shop had a tank he would let us use, but he sold it. Now the guys take their parts to a local metal plater for a boil. The plater lets them at the tank. It's not something you want a plater to do for you. A gunsmith would have a tank, but may or may not understand blackening a slow rust finish.

I've looked at steel roof gutter for a barrel tank, but it's too light to boil on a stove, and galvanized metal will create nasty zinc fumes. Track Of The Wolf suggests using steel gutter. I scald barrels to "set" the brown finish in a ABS pipe with a cap on one end. I bored a 1/4 inch hole in the bottom for drainage (more later on this). Slide in the barrel. Clamp the pipe upright to a sawhorse. I use a plastic bottle with the bottom cut out for funnel. Boil a large pot of water and pour into the funnel. Watch out for spashes! The barrel will cool the water; I open the hole in the bottom so I can keep adding hot water. Scalding takes only about a minute. Longer exposure will turn the brown to black.

Cure the finish with oil. This is "rust" and you don't want to remove it with a chemical in the oil. Don't use rust inhibitors or penetrating oils. Birch-Casey Stock Wax is a good choice. Black powder shooters like to stay away from petroleum oils because they harden fouling. Curing takes about a day. So I cure for about three days. After the "cure" you can apply any type of oil. No sense rushing any part of this process. You're going to have the gun for a couple hundred years.

I finish the metal with Birch-Casey Stock Wax. This stuff is good for metal, leather, wood. Furniture wax is good too. Don't use the furniture cleaners. They're solvents, not waxes. I've heard that Kiwi neutral shoe wax works, but I've not tried it.

This process is hard to screw up, but it can get tricky with the degrease and covering the bald spots. Sooner or later with elbow grease, acetone, scrubbing, and application of the browner the part WILL start to brown -- unless it's got a varnish or something on it you missed.

I've not used the Tru-Blue, but it should work like the brown. These are oxidation processes, and boiling turns iron oxide black-- going from Fe2 O3 to Fe3 O4. Should work for Tru Blue also. The guys at the shop swear by Tru Blue for bluing.

I've not tried Birch Casey Plum Brown. It's not a slow rust process, and the parts need to be heated. I much prefer to set up a process and spend ten days at it. If you're working on a fine piece, there's no hurry to get the finish finished.

I've tried cold blue, super cold blue, extra super cold blue. Sometimes it works, sometimes not. Slow rust will work for steels. Steel alloy as found on newer guns may have problems. But an older guns and black powder rigs should brown up just fine.

Track Of The Wolf Inc. has a Technical Tips link that discusses brown, blue, and some other items. The articles are .pfd format which can be read by Adobe Acrobat (free download). Yeah, I know, plug-ins are a PIA, but this is a simple one, fast to load, and useful.