How to Colour Steel With HEAT

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Introduction: How to Colour Steel With HEAT

How to colour steel with heat (hot oil finish) is a simple but effective way of achieving a desired colour of choice.
The colours are fantastic and often come out in a beautiful two-tone shine. There is something really rewarding about this technique. Not only does it give you an alchemical feeling of satisfactionbut it also gives the metal a finish to stop corrosion.

Step 1: Preparing Your Materials

You will need:

-2x containers (one of them preferably being metal for the oil)

-oil

-unleaded petrol/Acetone/Terpentine/Rubbing alcohol or any good degreaser

-metal object/s (I used mild steel, Please note this method should NOT be used on tempered/hardened steel as you will effect the properties of the metal)

-something to hold your object with i.e. pliers, mole grips,...

-heat source

-protective glove (optional)

-wet towel on hand for safety

In Explanation:

-An old metal container (I know, a plastic container is pictured but always use a metal one) filled high enough with oil to completely submerge your steel object would be ideal. You can experiment ultimately what oils to use. Try it on some unimportant pieces first. I found through my bluing adventure that different oils do act slighty different but ultimately everything I've used has done the job. For this Instructable I'm using thread cutting oil. I have also had good results with 5w/30 motor oil, I've also used two-stroke oil with good results. It's worth noting that there can be some additives in motor oil that release hydrocarbons when burnt which is a known carcinogens to the body (in other words: Bad Stuff!)

Your container should be relatively larger than your object.

-An old container filled with your chosen degreaser (unleaded petrol...)

-Your desired polished metal object/s (very important!: Make sure it is made from Mild Steel or Titanium. You can not do this method with Aluminium because it won't reach the temperatures required for bluing, it will just melt. Trust me, I'm speaking from experience :) )

I have cut and polished 4 pieces of mild steel to demonstrate different colour stages. The object on the left is a custom mild steel potentiometer knob!

-Something to hold your piece with, make sure it's appropriate to hold it with so it doesn't get too hot in your hands. It would be a good idea to get some gloves on.

-A heat source. That can be a pen torch (pictured), a blow torch, a heat gun, a gas hob (which I am going use) or anything that will provide you with enough heat.

Please note: As you are working with heat, please be smart, use your common sense, do the bluing process in a well ventilated area and keep a wet towel to hand.

Step 2: Cleaning Your Metal

For the process your metal should be nicely polished for the best results.
The more shinier the polish the more your end result will glow.

I can't stress how important the degreasing step is! Do NOT wipe/touch your metal with anything after degreasing as the whole purpose of cleaning was then for nothing. Even a fingerprint will affect the consistency of the colour.

Now securely hold your piece with whatever you have chosen.

In my case I drilled/threaded the metal piece and made a holder with a threaded end. This is not necessary as long as you can hold your item appropriately and not cover where it is to be heated.

Next wash your piece in your chosen degreaser for a minute or so to get rid of all grease/fingerprints that was on the metal.

Then remove it from the degreaser, don't be tempted to wipe it off with anything. Just let any residual matter evaporate/dry.

Step 3: Bluing

Now you can start.


Apply heat to your object and heat up gently and equally.

As I'm bluing round pieces I slowly and evenly rotate the piece over the flame to equally disburse the heat.

Be patient in the first few minutes as the metal needs to reach the temperatures where it changes colour!

Once you see it turn golden, the process has started and colours will change fairly quickly!

Sometimes at this point, I come just a fraction away from the heat to go through colours a bit slower.

It will first turn gold, then orange, then red, purple, blue and then dark grey!

Step 4: Finishing

Once you get the colour you want, go outside to your oil container and fully quench your object into the oil!

Note: I know a plastic container is pictured but always use a metal one!

Bear in mind not to touch the walls of your container as you don't want to disturb the process of what's happening!

Remember the oil is probably gonna release some smoke/fumes once the piece is quenched so as said before: please do this step in a well ventilated area.

Once it's cooled down, take the object out of the oil and place it on a piece of paper/cloth and let it set for about 20 minutes. Alternitavely you can leave it in the oil bath to stabilize.

Then wipe off all excess oil and look at your beautiful finished object!

Step 5: Admire Your Finished Product

Above you can see some example pictures of the colour shades that can be achieved with this techniques.

Have fun doing it!

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52 Discussions

I'm trying to be positive and constructive, and think this is: for an amateur to stick a very hot torch-heated metal object into a plastic container filled with oil is simply dumb (ok, more polite: "irresponsible") at best, highly dangerous at worst. I'm a professional knifemaker and use many very high-temp methods including quenching 1,600°F steel in pre-heated oil - I know what I'm talking about, 'cause I still have 10 fingers and my eyesight. You'll probably be fine following these instructions - you'll probably be OK driving home a little drunk, too. I wouldn't recommend either.

I don't understand why you are submerging it in oil? Isn't the point of the acetone to degrease, why would i grease? I am using bronze, is it for a polish?

I've never done anything like this but want to try. Could I use stainless steel earrings that I have got? Thanks

looks nice but you are using what is known as heat treatment which will darken steel

not using bluing salts as in gun bluing of rifle barrels all in all very nice instructable

sorry my 2 cents

1 reply

I found that heating will turn steel silver ~> gold ~> violet ~> blue. I believe the change of color is due to a growing thickness of an oxide layer. (meaning oxygen atoms are able to attach themselves to the outer layer of the steel)

We did this with an electromagnet! Check out the video:
https://hackaday.io/project/21947-makers-vise/log/60914-coloring-steel-with-magnetism

The color is oxide, but I believe you can scrape it off. When heat treating a forged blade you get the whole knife glowing, then submerge just the blade in the oil for 8 seconds. Then you pull it out and scrape off the oil along the blade edge. Next you hold it in front of your heat source until a blue oxide layer covers the whole blade edge. Submerge in water and scrape edge. Repeat 3 times.

1 reply

The color is not oxides, when steel is heated at relatively low heats (300-600 degrees Fahrenheit) it changes colors from light yellow to a deep blue, after 600 it turns back to a steel color. Oxides come after its been heated to a red heat and cooled.

just fyi, the old school method of case hardening steel is to get the piece so hot that a magnet will no longet stick to it and quickly quench it in used motor oil. The steel will pull some of the carbon out of the oil while quenching and harden the outer portion of the metal. Ive used this method in a pinch to make a tap from a cheap mild steel bolt to chase out galled female threads.

2 replies

Usually they would pack the parts in crucibles and surround them with leather, wood, coal,bone etc...They would heat them up to 1200°F to 1500°F and hold them at this temp. for 6-8 hours. Then the crucibles would be removed from the furnace and placed over boiling hot water and air would be bubbled through the water and the parts would be dropped into the water. The differing rate of cooling for each area produced a different color creating that rainbow effect. All those materials the leather and bone the coal where sources of carbon and other trace elements. The steel was mild steel and had very little carbon content. This is how Colt made their rifles and pistols prior to Civil War you can read all about the process. The book claims they used wait for it "boiling gasoline" not making this up to clean them. If I remember right they then heated them up a bit and applied fish oil orignal and I think latter switching to linseed oil to protect the finish and give it that wet look. This is all from memory so I might have left some stuff out. After the Civil War they switched to another process. You can also heat the oil to create different effects. Cooking off the more volatile hydrocarbons leaving the heavier ones produces a different effect yet again. Have proper ventilation and use proper modern safety gear!

highfour, case hardening is a bit different from what you describe.....

Usually, the steel needs some time in a medium that will allow carbon to penetrate the surface, and we are talking 15 minutes to several hours....

Nowadays, even mild steel does have a certain amount of carbon in the alloy, which can explain your observations, if you google "super quench," you should find a waterbased quench that is rumoured to do the same, but in my humble opinion, water can do just that as well....

But hey, as long as it works....

Ok you gotta help me out here...when I was studying mechanical engineering a good few years back a project I done involved using a compression fit of 1/4" thick plate steel into 1" thick steel rod, both mild steel. The rod was heated and the plate 2" square was inserted and the rod shrunk onto it. The plate turned blue just like you ible and I was told this was an effect of compression fitting....the rod didn't change colour even though it had the heat applied to it so was it actually the compression fit that changed the plates colour

5 replies

The "turning blue" process has nothing to do with hardening of the steel, or its compression. It is caused by a layer of oxide that forms when the steel is heated. The thickness of the oxide is a function of how hot you heat the steel (The color is due to interference of light reflecting from the surface of the oxide coating, and light reflecting from the oxide-steel interface). The hotter the steel, the further the oxygen can diffuse through the oxide coating, so the coating builds thicker before it protects the steel from further oxidation.

To shrink, I assumed you heated the steel plate only, to expand the hole in it. This heating forms the blue on the plate. Now you slide the cold rod in, and the plate cools, gripping the rod. While the rod may heat some by conduction, it wouldn't get hot enough to start the color-forming process. (You say the rod was heated, but it couldn't have been, as it was on the inside. You heat the outside member only when you do a shrink fit.)

For hazzalandy: carbon content has nothing to do with the color process, it is only the temperature you heat to, and to a lesser extent, the time spent hot.

In the automotive world this is a common practice. In fact most guides no matter their material cast iron to bronze and often bearing races are installed the same way. The part that is to race the other is heated normally up to about 220° especially if it is an aluminum casting like a cylinder head. The part you want to place in the receiving part is cold often just placed in a freezer for a few hours. The parts can often be put together with little or no forces need and friction lock together and the one parts shrinks and the other part expands. Ferrari installs valve seats in their aluminum cylinder heads via robot. The head is fixtured and and an arm holding the valve seat moves the the proper location. The robot gives the steel valve seat a quick blast with liquid nitrogen and drops the seat right in place. It repeats the process adn by the time the head moves on to the next station all the parts are seated presumably for the life of the head. 500°F-600°F is often all that is needed and the parts can be done over and over again you just have to clean between each attempt. I agree used oil works better and adding some copper and graphite seems to deepen the color and add more purple or plum to it. Most knives, rifle receivers and barrels are heated to at least 1200°F and cooled and drawn at 490°F-700°F. If you look at the temps that Tenifur(SP) and Melonite(sp) and early Pakerizing processes used this is nothing. Tenifer get's up to (1077°F) last I checked and was the 5th step in Glock heat treating after that they Pakerize it. You can get a IR non-contact thermometer for less than $20 at Harbor Freight. If you do not get crazy and over heat the steel there is no reason to be fearful of the process. Knowledge is the power and fear is the opposite of power it cripples the mind and the body and almost always guarantee's a poor decision will be made. Being prepared is important if you can not measure the temp. of the steel than do not even try this on something that is anything other than artistic in nature! No one can even tell you what the heat treat is on a 1895 Mauser for instance yet we do not wet ourselves before we shoot one! We have all kinds of rifles and shotguns with recievers made from non-Fe alloys again we do not give it a second though or break out the hardness tester.

(I may have over-simplified this )The higher the carbon content of the steel, the lower the temperature needed for tempering (turning blue). The rod would've probably been a lower carbon content, and thus would have been less affected by the temperature.

Cheers for the reply, I guess I never really knew the carbon content and just presumed they where both about the same, i still feel that the pressure had an effect on it though.

The actual tempering effect turning the metal pretty colours is caused by thin film interference. Essentially the heat creates a transparent oxide layer on the steel. These build up to reflect (and absorb) certain frequencies of light. The only way that I can see that pressure could affect this is if it created microscopic ripples in the surface, which encouraged deposition.

Also the rod would probably be a more ductile steel, so therefore less carbon, because it's a rod, and therefore it had to be drawn into that shape without breakage.

Sorry to not bet hat helpful...

Your concept is great. Oil quenching can result in some great colors. I've done a lot with a propane torch and then clearcoated the final product to protect it from oxidation.

But two things made me very nervous when reading this.

1. NEVER, NEVER, NEVER use gasoline as a cleaning agent. Gasoline is made to do one thing--Explode when exposed to heat. Vapors from gasoline are explosively flammable. Acetone or mineral spirits are a much better choice.

Your use of plastic containers is just careless. You're dealing with 600-700 degree steel. One slip and you've melted though the plastic, spilling oil everywhere.. Use a steel can or tray. Every picture shows a plastic cup.

I'm not some safety fanatic. But using gasoline as a cleaner is just a out the most dangerous thing you can do in a shop

1 reply

he said he used metal containers, those plastic ones were just as an example to display the liquids.