Heat coloring

Mike Davis

Mike Davis

Joined
Feb 7, 2006
Messages
1,327
I am in the process of heat coloring some bolsters as well as a few tattoo machine frames.Does anyone know the heat range of coloring blue and purple? I am trying to find specific temps, but my oven only goes to 500 degrees, and that just gives me brown. Any other heating i do is by forge and propane torch, and i don't have a thermocouple in my forge to show me temps. Any information would be greatly appreciated.

Also pics of my new shop will be up soon, just got my lathe up and running, and the new forge is almost done :)

Thanks

Mike D
 
Try a propane torch under a metal plate. It is more difficult to control direct heat but it can be done. If you use a metal plate under it you will be able to control it easier.
 
I read in a post a long time ago that if you substantially increase the time at temperature you can obtain the color you are looking for at a lower temp. The example I remember was quite a long time(hours) but I can't remember the specifics. Never tried it either...
Matt
 
Use a thin plate on the kitchen stove probably about 60% on . Have some tweezers handy and as soon as it gets the color you want move it off. If it goes past the color you want then buff it and start again. Yes this works for flat pieces only. Try the oven or a torch as mentioned for irregular shaped items with a low gentle heat. Frank
 
A quick Google search returns this page:
http://www.threeplanes.net/toolsteel.html

Scroll down a little past halfway, to "Tool Steel Color vs Temperature", and there's a neat little chart. Looks like your oven is just "perfect" for the brown/purple cutoff at 500 degrees. Purple rings in at 520, dark purple at 540, and blue at 575.

Takes me back to a couple years ago working in the machine shop in college, when the shop prof would crank up the speed on the lathes to set speed records on the basic part they had people make in the basic class. Obviously jacking the speed up meant more heat, and he'd watch the colors change on the chips coming off and recite the approximate temperatures. Very very cool to watch the steel change through the high contrast purples and blues.

Edit: Guess I should point out the page is specifically for O-1 Tool Steel...but I assume the temperatures don't change much for the different types of steels (how much could they really?), and you didn't mention a specific one.
 
Just buff your pieces up and use a propane torch have a bucket of water under the work so you can stop it. My experience is different steel colors a bit different at different temps. I Have had 1095 turn a golden brown at 400 and blue at 450 (why). I wonder if the atmosphere effects this
 
Mike,
I know this is not going to sound right, but I have done this with hundreds of bars of damascus, I heat color all my damascus for sale. I set my oven for 350F and cook the pieces for about 20-30 minutes. I get all the colors from straw to purple. The longer you cook the deeper the color. I am not sure this will work with hardened bolsters. I do wash the pieces in hot soapy water prior to cooking. The amount of oxygen does affect the color.
I know many will question me on this, but I tell you it works, if anyone here has been to the badger or wolverine shows have seen my steel this way.
Thanks,
Del
 
I tried it with a torch, got decent results, but was trying to get something more even. I have got the torch thing down quite well. I was thinking of getting a heat treat oven for more consistent results, would help out for working with O-1 also :P


P.S. Delbert, i want to come visit. I know you just had a baby, Let me know how your schedule is, and ill come up and share some ideas :)

Thanks for all the replies
MIke
 
I would like to try to get a case colored effect on 1018 fittings sometime. Any ideas on how to do that without actually case hardening the steel?
 
Hi Joe,
There's a thread over on Fogg's from a couple of years ago that gave a good run down of one process. Supposedly, the piece needs to be held at 1375*(?) to color case harden, but colors apparently will form at lower temps. Still need the long hold time and water quench.

Good luck with it, Craig

I peaked at the thread and it seems like as low as 1200* can form colors, better than 1350* and preferably 1400* to harden.
 
cden said:
Hi Joe,
There's a thread over on Fogg's from a couple of years ago that gave a good run down of one process. Supposedly, the piece needs to be held at 1375*(?) to color case harden, but colors apparently will form at lower temps. Still need the long hold time and water quench.

Good luck with it, Craig

I peaked at the thread and it seems like as low as 1200* can form colors, better than 1350* and preferably 1400* to harden.
Click to expand...
Thanks. I'm not worried about hardening the piece, just the purty colors:D
 
Take your piece and clean it perfectly with acetone.
Heating colors are a form of oxydation, so any impurities present on the piece will produce an uneven coloring, no matter how careful you are with heating.
Use a propane torch or kitchen fire.
By keeping the piece with pliers or tweezers (caution, they will get HOT!) keep the piece in the column of rising hot gases ABOVE the flame.
Start a good ten inches over the flame, than lower it slowly. The process will take patience and time, so if you have to produce a lot of parts, it's better if you take an electric oven with a professional termocouple (kitchen ovens won't reach the necessary heat nor be accurate enough).
Watch closely as the piece goes through color changes: pale yellow, yellow, dark yellow, brown, purple and, finally, blue.
The slower and more even the heat, the more even the color.
As soon as you reach the proper color, quench in water.
It's not the proper method to heat treat, but since you just want color it's the easiest way.
EVEN and SLOW are the keywords.
If at 10" you see the piece changing color and then stopping at a given color, and not running through the whole range to the color you want, just lower it maybe an inch, and watch closely to see what happens. if it doesn't get hot enough, lower it another inch, and so on, waiting at least a couple of minutes to see what happens.
I say 10" because that's the distance I use on my coal forge, but for a propane kitchen fire it may be too much (or too little, who knows?).
Remember this coloring is on the very surface only. Simple handling will wear it off with time.
 
Color is dependent on temperature, alloy and as Alarion mentions ,surface contaminents....Don't confuse temper colors [~400-600 F] with color case hardening.The second takes place above critical temperature and organic materials such as leather scraps are added to color the steel.
 
Its like Delbert said, time and temperture can give several different colors, the longer the soak the different colors will appear to a certain point, you might have to raise or lower your heat or soak times to get a different color from different steel. Titanium turns a real nice gold when soaked 15 minutes at 800, a high carbon steel would go though all the heat colors and turn gray at that temp and time. Experimentation is the key.
Keep it clean and start at a low heat and a carefully timed soak time, Raise your temps as you go, once you get it figured out write it down and you'll have it next time. Just remember time and temperature.

Bill
 
I'm wondering how you can get a multicolored peice without case hardening.
 
Very sharp heat differential is the key, like with an oxygas torch with a needle nozzle.

With titanium, be careful: titanium has a property that is "shape memory", and heating it a lot can cause some bad distortion in some manufacts. It's a weird thing.
 
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