Blackening Steel With Used Motor Oil

Have you ever wondered how to get a beautiful black finish on iron or steel? There are several methods, but this one is easy and the only chemical required is used motor oil.

Using this method, you can obtain a permanent finish on the metal. It does not scrape or wear off like paint but it is embedded into the surface of the steel itself. I’m not certain, but there may also be a certain degree of hardening that takes place on the surface of the metal due to tempering and increasing the carbon content. Here’s how I’ve had it explained to me: This happens because metals like steel and iron are slightly porous and when you heat up the metal, it expands and opens up those pores enough to allow the carbon molecules into them. When cooled, the metal contracts and tightens those pores, holding the carbon molecules in. This will only work with used motor oil because it is contaminated with carbon. The blacker the oil, the darker your finish will be. I’ve used some motor oil from one of our vehicles that has had a lot of miles between oil changes.

The materials you’ll need are:
- Two cans (a small can and a #10 can that can fit over the top)
- Used motor oil
- A propane torch, forge or some other way to heat the metal sufficiently
- Pliers or tongs with sufficient length to hold the material and fetch it out of the can
- Safety equipment (safety glasses and face shield, welding gloves)
- Soft, absorbent cloth for wiping the oil

Do this at your own risk. This is potentially dangerous and could cause fire, burns or explosive reactions. Do NOT use cast iron because it could crack, ruining your metal and causing a dangerous condition. Only do this outdoors on a non-flammable surface and away from any flammable materials. Start with a clean surface on your steel, devoid of rust, paint or contaminants. It should be shiny. Fill the smaller can with enough oil to cover the surface of the metal you are heating. Heat the surface of your metal evenly and thoroughly with a propane torch or forge. When the surface starts to discolor to a darker color, it is ready to drop into the oil. Carefully drop it into the oil so it doesn’t splash. Immediately cover the smaller can with the #10 can and back away. You’ll hear the oil boiling for a minute or so. Wait another minute until it stops boiling and smoking. Uncover the smaller can and remove the steel carefully to avoid scratches or dropping your metal. Let it cool naturally. It will take longer for more massive pieces. Once it has cooled to the touch, you can wipe the excess oil off with a cloth.