Introduction: How to Colour Steel With HEAT

Picture of 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

Picture of Preparing Your Materials

You will need:

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!


Akajira (author)2017-09-06

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

thebear1 (author)2015-02-25

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

FievelM (author)thebear12017-06-08

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:

Chris Project (author)2017-03-26

what kind of oil are you using?

RandyD63 (author)Chris Project2017-05-02

Did you ever find out what oil they were using?

Boverpho (author)2015-06-29

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.

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.

highfour305 (author)2015-02-25

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.

JohnL595 (author)highfour3052016-12-16

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....

Tallanted (author)2015-02-28

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

bpark1000 (author)Tallanted2015-03-03

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.

JohnL595 (author)bpark10002016-12-16

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.

hazzalandy (author)Tallanted2015-03-01

(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.

Tallanted (author)hazzalandy2015-03-01

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.

hazzalandy (author)Tallanted2015-03-02

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...

brianfss (author)2015-03-01

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

IanL9 (author)brianfss2016-09-01

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

brianfss (author)IanL92016-09-02

You're right. I reread the instructable and he did say that. But people sometimes get more information from the pictures, so using metal ones would have been a better choice. My point about the gasoline as a solvent is still spot on. Never use gasoline as a cleaner!

IanL9 (author)2016-09-01

I have a plain stainless steel necklace that I plan on bluing. I'm just wondering if the metal clasp components or links may break due to heating. (penny for scale)It would probably be heated anywhere from 490-600 degrees for a spectrum of the different colors. it was only 8 bucks but I'd rather not break it.

wesley.canfield made it! (author)2015-10-19

I didn't have a good degreaser on hand, and i didn't feel like looking for one, but you can get neat effects if you dont use one. I just wish i could get a picture that does the color at least some justice...
I sealed it with rennaissance wax to prevent rust. It almost has a cosmic effect to it.

IanL9 (author)wesley.canfield2016-09-01

A few months ago i turned a nail blue (didn't use the quenching process, as I hadn't seen these instructions at the time) and the color seems to be very visible in daylight, I think because of the color temperature.

dratman (author)2016-05-21

Please do not keep a container of petrol anywhere near flame or heat. It is very explosive. I suggest using one of the other solvents listed, and do not put a container of any solvent into the room where heat or flame are being used.

Secretsquirrel16 (author)2016-01-17

Is there a way to do this on large pieces of steel thin gauge. Or suggestions I'm thinking of doing this as a backsplash for a kitchen?

ColterS (author)Secretsquirrel162016-05-11

Did you ever try it with bigger material I'm curious to know what you did

PhilipC32 (author)2016-02-27

What type of oil do you use?

AprilW7 (author)2015-12-03

It is so amazing what you can do with metal. As an artist, I think it would be fun to use some different color metals in some of my sculptures. However, I wouldn't want to try and temper the metal myself. If you mess up the process the metal will be weak and fragile. So, it seems best to leave it to the professionals.

jgreen60 (author)2015-05-10

I just tried this on a steel ball for the hell of it and it worked fine but when I was putting it in the oil I hesitated a bit before I dropped it in and the end result had half of it really dark and the other half a little less dark but I must say that it came out really cool

tomatoskins (author)2015-02-25

I've always love the look of blued steel. I can't remember, if the bluing is a form of oxidation or not.

AOSA (author)tomatoskins2015-04-24

errr kind of, bluing is weird stuff, Google is your freind

Sir Bacon (author)2015-03-07

Does this work on metal that is silver plated? Or will I damage it, I hoping to try this on my trumpet mouthpiece for decoration

usafbrat (author)Sir Bacon2015-03-14

Yes, this process will damage any silver plated material.

meeeeep (author)2015-03-04

Man, why can't my things be this awesome?

A1v1n1 (author)2015-03-01

How would you dip it in oil for larger objects? Would pouring the oil over it be sufficient?

Kinnishian (author)A1v1n12015-03-01

Pouring over would be a dangerous idea and could result in combusting oil flame. The method for larger objects is a larger bucket of oil :). The reason why the oil doesn't blow when you dip the red hot metal in is the quantity of the oil and the lack of access to oxygen. Remember you'll also need a bigger flame for bigger objects

Metal_maestro (author)Kinnishian2015-03-03

Also keep the heat capacity of the system in mind. Just like the difference in boiling a cup of water versus a gallon of water. You will need enough oil to absorb the heat of the metal safely. I have quenched a few things and more liquid is always better than less.

tacamaral (author)2015-03-01

Really cool - I've used the same technique for blackening pieces of steel for some projects, but the other hues are very pretty! I should have made the last project with blue steel, not black.

Anyway, just a word of caution: galvanised steel, when heated, gives off very dangerous fumes. Take care, everyone.

As does Nickle and Many Others ~Do your research being poisoned from fumming isnt fun

Pawl (author)2015-03-02

Did something like this a couple years ago, but purposely used old dirty motor oil instead of clean oil, and it gave the metal a nice even solid dark black finish.

timstoy (author)2015-03-01

Back in the 60's and 70's when we wanted to trick out a bicycle frame that was chrome we would take it to a machine shop after we had stripped it clean and removed all parts. The shop would put it into an oven and heat it evenly until the chrome turned black. It was fine but jet black. Then reassemble it. It looked amazing. Chrome was so"common". LOL

Bookrestore (author)2015-03-01

very good presentation! If a person has a little extra space they can make a Coffee Can Forge (also found in many project examples) and install a decent regulated and temp. probe into the side of the wall of the forge. This concentrates a perfectly even temperature environment without spending $3500 on a digital kiln and gives you a perfectly even heat throughout your metal piece in order to gain a smooth consistent coloration. Also, plunging the item into the oil is important to avoid temperature 'leeching' and causing inconsistent colors. (Often seen in cheaper firearms from certain gun makers some of us may be familiar with).

You are dead on in your science and commendations for safety. And plastic containers should be an oil container absolute no-no since occasionally the oil will catch fire...keep an A-B-C Fire extinguisher on hand a phone and cool head!

BiffIsGod (author)2015-03-01

Love the colors your getting there! In also interested in how you made your steel pieces particularly that potentiometer knob! Any plans for another instructable on how you made them?

randy.postlewait.1 (author)2015-02-28

noe tell me about the Fumes~Safety First

fzumrk (author)2015-02-26

One safety note: I've had motor oil ignite before when quenching steel in it. I don't remember the exact circumstances, so I may have been working with steel at a higher temperature than you are. Anyway, I would put the oil in a metal container and have a metal lid you can put over it if it does catch fire to smother it.

I looked it up, and the flash point of motor oil is 420 to 485 F. Blueing temperature is about 639 F so I'd say igniting the oil is a definitely possible.

eruger (author)fzumrk2015-02-28

Also a good idea to an ABC extinguisher handy, since burning oil can sputter and splash burning oil around and catch other things on fire. Sometimes things you wouldn't think would burn, and splashing with water can spread it. Goggles and a respirator would also be a good idea.

Midgaardssmeden (author)fzumrk2015-02-26

fzumrk, you're absolutely right!

Never, ever use a plastic container when you play with oil and fire!

Depending on the size (or mass) of the object that is heated, and then quenched in the oil, the temperature will rise, and it's possible that the oil will catch fire, and then in seconds you will have a burnt out container and burning oil everywhere.....

Well, it may not be that bad, but the possibility is definately there, especially if you'r using old, used motor oil (as I do sometimes). There might be fuel residues in the oil, be that gas or Diesel, and that will actually lower the flash point for the oil to a point you don't know.....

Before you start, have a little session of "What can possibly go wrong," or a risk assesment as it's called if you are a professional, and try to cover all possiblities.

The Fire Brigade are nice people, but I think that we all prefer them to stay home at the firehouse ;o)

eruger (author)2015-02-28

Nice 'ible! To help with some confusion that might arise from terms: When a lot of people say 'blueing' they mean a different process, using a chemical, which is what is used on most firearms:

That process is safe for heat treated metals by the way, but it's not as pretty :D

The process you're showing here (and very well I might add) is often called a hot oil finish in metals (not to be confused with cold oil, which is just rubbing drying oil on it). I prefer boiled linseed oil by the way. Walnut or any other drying oil (aka alkyd) can be used though. Many motor oils don't contain alkyds btw, so they may or may not provide the same protection. (What brand/type did you use?)

Fikjast Scott (author)2015-02-28

very artistic, well done

Suraj Grewal (author)2015-02-27

I've seen my tamperd steel getting rainbow like colors when heated....but this is the first time i saw soeone employ that techneq

Midgaardssmeden (author)2015-02-26

Nice 'ible, but do keep in mind that if you are doing this on hardened steel, you will ruin the properties of the steel.....

When you quench/harden steel, you take it up to a certain temperature, the critical temperature, then quench it in water or oil to harden it.

The hardened steel then becomes very hard, and unfortunately, very brittle. To soften the steel, it is now tempered, which is in effect what you have just done.

The steel is heated as you describe, and the colours you see are in fact oxidation that occurs as a result of the temperature. Blacksmiths has for litterally thousands of years used this technique when heat treating steel. A knife is usually taken up to a temperature where it becomes golden, or the colour of straw, and this takes some of the hardness out, so that the steel is not brittle anymore. The colour of straw occurs at about 230 degree Centigrade, so you will see that it happens at fairly low temperatures.

The higher temeprature, the darker colours, and the softer steel.....

You may know this from sharpening knifes and tools on a benchgrinder. Suddenly the blade turns blue, and then black......

When that happens, the dark area is ruined, and very soft. Usually, you can get away with grinding off the damaged area, as it tends to be quite small.

There are techniques for blueing steel at low temperatures, but this is done with a chemical treatment.

- Not trying to be patronising or negative, but it would be a shame to ruin a good knife or tool out of ignorance ;o)

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