Bluing is one of the best solutions to add color and extra protection layer to steel. Most people think only carbon steel can be blued. Although they are partially right when talking about traditional bluing, we will discuss if there are decent bluing solutions for stainless steel.
Can You Blue Stainless Steel?
Rusting under regulated conditions results in the formation of surface oxidation, which is subsequently chemically transformed to black oxide in conventional bluing.
Since the chromium, vanadium, and molybdenum concentrations in stainless steel are greater than in traditional alloys, oxidation does not develop immediately. Instead, the oxidation can be forced by adding certain salts specifically made for stainless steel bluing.
It is possible to blue stainless steel using different methods than traditional bluing. These methods, primarily hot-bluing ones, will create oxidated layers similar to Fe3O4 that you get on carbon steel. Cold bluing methods use chemical processes to color the stainless steel but don’t provide additional protection.
Since traditional bluing doesn’t work on stainless steel, I won’t dwell too deep into how it works but rather explain working methods separately.
Hot Bluing Stainless Steel
416R, which I’ve hot-blued multiple times, is one of the easiest stainless steel to blue.
Blackening and staining stainless steel may be done with two commercial formulations. Salts from Du-Lite and Brownell’s Oxynate 84. They’re more difficult to work with than plain bluing salts, but they’ll get the job done.
They require some experience to get a clear finish, even though the results will never be the same as bluing carbon steel in a traditional way.
To blacken stainless steel, I use Oxynate 84. Also excellent for steel with a greater silicone content, which turns reddish or plum-colored with normal bluing.
Most smiths know about these hot bluing methods, and you may ask a local smith that specializes in bluing to do it for you. Although, you will likely have to disassemble non-steel parts on your own.
Cold Bluing Stainless Steel
Stainless steel can be cold-blued, although there are certain issues with wearing an object that has been cold-blued.
Stainless steel is cold-blued via a chemical plating technique, which offers less protection for the metal but alters its appearance. Copper or selenium plating and oxidation are the best cold blue solutions for stainless steel. An easy-to-apply, black finish is created as a result.
Cold-bluing stainless steel employs an acidic solution like Caswell Stainless Steel Blackener 370. It’s fantastic for getting color, but you won’t get the sheen or mirror-like finish you would with standard bluing.
These metal plating solutions are not meant to be applied to clothing or other objects you will be in constant touch with. Cold-blued stainless steel objects using these chemicals shouldn’t be used for lengthy periods and might cause skin discoloration or heavy metal absorption via the skin.
Necessary Equipment for Bluing Stainless Steel
Before we get to the procedure of bluing stainless steel, it’s important to mention all the necessary equipment.
I will be explaining the procedure from the perspective of using Brownell’s Oxynate 84 since that’s my personal preference. If you decide to use Du-Lite 3-0 Salts, read their instructions and apply them to the procedure and choice of equipment.
- Chemicals– You will need the following chemicals: Dicro-Clean 909 Cleaning Solution, Oxynate No. 84 Bluing Salts, Water Displacing Oil, and Hydrochloric Acid.
- Tanks: A common setup requires six tanks. One for the Oxynate No. 84 Bluing Salts bath, one tank for the Dicro-Clean 909™, one for the cold water rinse, one for after cold rinse, one for after hot water rinse, and one tank for Water Displacing Oil. You can use black iron or stainless steel for the 909™. However, I recommend using a black iron tank for Oxynate No. 84 Bluing Salts. Tanks size depends upon the objects you want to blue. Sometimes, simple stainless steel buckets are more than enough.
- Thermometers – You will require two thermometers for Oxynate No. 84 Bluing Salts tank and the 909 Cleaner tank.
- Something to stir with – Keep the bluing bath well-stirred by stirring it regularly and thoroughly. Use a tiny shovel to stir the bath, or make one on your own. It is possible to make this tool out of either black iron or stainless steel.
- Heat source – You will require at least one burner for bluing salts and two hot water burners.
- Black iron wire – You will need black iron wire to tie around any object you want to blue and lower it into containers.
- Stainless steel dipper – The solution can be pretty chaotic when boiling. It would be best if you had a dipper, ideally made from stainless steel, to add salts or water into the solution while being safe at the same time.
- Acid tank – I recommend using pyrex, gel-coated fiberglass, or polypropylene plastic containers if you need to use Hydrochloric Acid as part of the Oxynate No. 84 bluing method.
- Safety gear – These chemicals are highly corrosive and dangerous for the skin. I can’t state enough how important wearing rubber safety equipment is. Essential safety equipment I use includes rubber gloves, a rubber apron, rubber boots, a full-face safety shield, and a filter mask.
How to Blue Stainless Steel: Procedure
At 240 degrees Fahrenheit, the bath solution should be briskly boiling. You can add small quantities of Oxynate No. 84 until the solution boils at 240°F. Add modest amounts of water to reduce the boiling point if the solution reaches a temperature greater than 240 degrees Fahrenheit.
The salts solution must be constantly stirred to prevent the formation of “hot” or “cold” spots. As you swirl the solution, be careful to move your stirring tool around the tank’s bottom and near its surface.
To preserve the strong boiling of your solution, you should lower the heat by roughly one-third after it reaches 240° F. and reaches a temperature of 240° F. Allowing water to boil will raise the bath’s temperature; adding water will reduce it.
Do not lower the heat on the burner to maintain a constant temperature; instead, adjust the salt-to-water ratio by adding salts or water until you get the desired boiling temperature.
Before dipping the metal into the solution, prepare all the surfaces. You can use polish, sandblast, bead blast, wire wheel, etc., to prepare the metal surface for blueing. Be cautious when polishing stainless steel alloys using buffing wheels since they might cause the metal to seem spotted.
Oxynate No. 84 is corrosive and can cause lasting skin and eye damage.
Always use a long-sleeved cotton shirt, heavy rubber gloves, a neoprene rubber apron, rubber boots, a full face safety shield, and a filter mask when working with it.
Keep a wide-mouth container of vinegar beside your bluing tank at all times. If Oxynate No. 84 comes into contact with your skin, immediately dip your hands in vinegar or splash vinegar on the afflicted area. Wash thoroughly with soap and water.
If Oxynate No. 84 gets into your eyes, rinse them thoroughly with cold water for 15 minutes before bathing them in a boric acid solution. Consult a doctor right away.
Suspend parts in a Dicro-Clean 909 cleaning solution to remove dirt, grease, oil, and debris. Mix the Dicro-Clean 909 Solution with 1 gallon of water at a rate of 5 ounces (by weight of Dicro-Clean). Heat the 909 Solution to 180° F. before immersing the pieces for 10 to 15 minutes. If the solution starts boiling, make sure to turn off the heater.
Rinse the cleaned parts in a tank of cold running water. To remove all traces of the Dicro-Clean 909, scrub the components well with a gentle vegetable brush.
Add cleaned parts to Oxynate NO. 84 BATH. At 240° F, the bath should be actively boiling. Normally, a component will become blue after 5 to 15 minutes of reaching the required temperature.
Rinse the blued parts in a tank of running cold water (not the same tank from before). After the pieces have cooled to room temperature in the cold water, inspect them carefully for blemishes, discolorations, or faults.
To remove or neutralize any lingering residues of Oxynate No. 84, soak rinsed parts in a tank of clean boiling water for 5 to 10 minutes.
Quickly transfer parts to a tank of water-displacing oil. After the parts have cooled in the water displacing oil, you may remove them, clean the excess oil and reassemble all the non-steel parts. Because new blue is quite fragile, I prefer to handle freshly blued items with care for at least 24 hours to allow the bluing to “cure.”
Limitations of Bluing Stainless Steel
Proper stainless steel bluing is possible only with hot bluing techniques, which are not practical with any stainless steel object. Some stainless steel objects cannot be disassembled and blued this way.
I use the cold bluing technique to blue stainless steel watches and similarly complex objects, though it only adds color.