Cold Bluing


0000 oil free Libron Steel Wool
Or make your own de-greased 0000 steel wool: soak steel wool in lacquer thinner for an hour, then rinse with spray 'brake cleaner'
400-600 grit wet/dry sand paper
Arm and Hammer Super Washing Soda
optional Sodium Hydroxide (Lye)
*optional Hydrochloric Acid (Muriatic Acid)
Gallons of distilled water and a pot to boil it in
A gallon or more of used (or new) motor oil
Lengths of 2 1/2" PVC pipe, sliced 1/3 deep lengthwise with caps glued on the ends after slicing to create troughs.  You will need one to pour boiling water in, one for soaking in a washing solution, and one to soak in motor oil when finished.
A propane torch like for use with soldering copper pipe
Cotton gloves
Long Rubber gloves for working with the cleaners
eye protection
Scott shop towel or similar lint free paper towel
Cold blue solution like Nu Blu
If there is rust, you'll need some Naval Jelly or Rust Away


1. Strip old bluing.
2. Sand off any rust and convert it with Naval Jelly or Rust Away
3. Polish the steel with wet/dry sand paper.
4. chemically strip oil from the steel. Do not touch with skin after this point.
5. Heat steel to open pores.
6. Rub cold blue on until desired color is achieved.
7. Buff steel with steel wool
8. Heat steel to drive out moisture
9. Soak steel in used or new motor oil for several days.  Slight warming of the oil can help get it soaked into the rust finish.
Materials Notes:
The Arm and Hammer Washing Soda should be sufficient to allow the steel to sheet water.  A more complete job however entails Lye to remove oils and Hydrochloric Acid (Muriatic Acid) to remove any organic material and rust.

Lye comes in some drain opener products like this

Hydrochloric Acid sources:
Muriatic Acid is sold as a pool cleaner and to remove excess mortar from bricks and can be found in the garden or pool area of any big box hardware store.  It averages around 31-34% acid.  It can be diluted in equal amounts with water to reduce it's strength for a bath or used in spots full strength if needed to clean an area that just doesn't seem to want to sheet water.  Remember to add acid to water, not the other way around.

You may also use any of these common cleaners:
Lysol Toilet Bowl Cleaner contains 9.5 percent hydrochloric acid
Sno Drops Toilet Bowl Cleaner contains 15 percent hydrochloric acid
Lime-A-Way Toilet Bowl Cleaner contains 14.5 percent hydrochloric acid. 

Use gloves and eye protection when dealing with bases and acids in the cleaning and rusting process.

The finish, blue, black or somewhere in between depends on the quality of the steel
The polish of the steel before you start rusting determines the appearance when finished.
Once the steel has been de-greased, do not touch with bare skin AT ALL until the entire job is finished.  Do not card with steel wool that have ANY oil or grease on them.
Used motor oil imparts a darker look to the finish, new oil imparts a brighter look.

Strip old bluing either with Naval Jelly or soak in white vinegar for 30 to 60 minutes, then rub lightly with 000 steel wool.

Sand the steel
You do not have to go any finer than 400 grit to get fine results.  Finer than 400 you are polishing the steel, and polished steel does not take bluing well.  600 grit will provide a more polished surface like many airgunners prefer, but it will be a bit harder to get the blue to take.  Use a water (whet) stone or an aluminum block with wet/dry sand paper on flat areas to maintain flats.  If you choose to use buffing compound on a wheel to polish the steel, you will have to use a solvent to remove all traces of the compound.

Degreasing is the key to success.  The steel must perfectly sheet water which will only occur if there is zero grease in the steel.  If water pulls away in a spot o the steel, that's a spot that needs further degreasing.  If water won't sheet in an area, neither will the cold bluing solution, and that area will not blue.

Degrease with acetone and a boil in a bath of Arm and Hammer Super Washing Soda.  If there are stubborn areas that won't sheet water, try scrubbing that local area with a toilet bowl cleaner containing HCL (hydrochloric acid)
For more a more complete job:

Dip parts in hot concentrated sodium hydroxide (lye) to saponify (to convert a fat into soap by treating with an alkali).  After a water wash, a short dip in hot (not boiling) hydrochloric acid removes any inorganic surface contamination and rust.  
In either washing case, the easy or the harder, a second rinse with hot distilled water followed by drying with a hot air blower finishes the prep.
You will have to clean the steel more than once. The cleaned surfaces must be completely wettable in the distilled water step; if the last time you rinse the part it is not covered by an absolutely continuous film of water it is not clean yet, and the rust will not cover the steel evenly in those areas.  Note any areas that the water does not sheet but pulls away from the steel and re-clean those areas.
After the degreasing, boil the metal in distilled water and allow to cool thoroughly.
After de-greasing, do not touch the steel with skin, no matter how clean you think you are.  Cotton gloves only.
Heat the steel with a propane torch to warm it.  Use a lint free paper towel (Scott shop towel for example) folded into a square and wet with cold blue solution and rub continuously over the steel until the desired color is obtained.  It may take ten or fifteen minutes of rubbing all over, re-wetting the cloth as you go.  Take a break from rubbing and re-heat the metal every 30 seconds of rubbing or so.
If an area refuses to take the blue, that is an area that is not adequately degreased.  Rub the spot with Muriatic Acid vigorously to try to get the blue to take.
Lightly buff the steel with 0000 oil free steel wool
Do a final heat of the metal with a propane flame to drive out any residual moisture, then soak in a warm motor oil bath for several days.  PVC pipe sections are an idea for a bath that is conservative with the oil.   Use used oil for cost savings and a slightly darker color of the finish.  Use new motor oil for a slightly brighter coloration.