Author Topic: preserving cool blue/purple oxide layer on metal?  (Read 465 times)

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Offline coppercone2

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preserving cool blue/purple oxide layer on metal?
« on: February 17, 2019, 12:10:52 pm »
I welded a small tool together and I noticed that after you clean off the originally present oxide, and you heat for a while, it turns this really nice blue/purple/cyan color pattern.

Is this oxide layer stable? It's made out of a magnetic steel.

I thought it looks better then paint, my idea was to mix up some clear 2 part jewelry resin, vacuum degas it, then paint the tool with it.

I don't mean a gun bluing, I mean a cool psychadelic neon blue color (kind of like when tig welding is done nicely).

https://upload.wikimedia.org/wikipedia/commons/8/89/Tempering_standards_used_in_blacksmithing.JPG

A mix between the 7-8-9 from the left.
« Last Edit: February 17, 2019, 12:14:48 pm by coppercone2 »
 

Offline Rerouter

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #1 on: February 17, 2019, 12:23:18 pm »
You should be fine if you coat it, the color is from a structure change in the metal from becoming an oxide, It increases in color intensity the thicker the oxide layer

In most metals this would make it likely to form rust at that location (technically you have started it rusting), with the color based upon the base metal.
Sealing it should holt the process and preserve the coloring, though you may want to de-gas the part at the same time to make sure you have pulled out any water vapour trapped in the structure. though this depends on how recently it was "colored"

A better example for others
https://i.pinimg.com/236x/81/d8/ac/81d8ac432d73260f0687bc3c4efe782c.jpg
« Last Edit: February 17, 2019, 12:28:02 pm by Rerouter »
 

Offline coppercone2

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #2 on: February 17, 2019, 12:29:23 pm »
fuck that means i need to make a bell jar. can i coat it while its hot to like 100C?

I only have the most ghetto vacuum chamber right now.

Also, this is one of my first projects with arc welding b/c I ran out of acetylene.

Will putting it in the toaster oven at like 450-500C for (what time period? max my toaster oven can do.. no kiln yet) relieve some welding stresses? Normally I only gas weld, I noticed its fairly brittle is you give it a hammer test (but I increased amperage since then, I had poor penetration first time). It's a Y shape made out of an old 3/4 inch bolt to use as a tape roller.
« Last Edit: February 17, 2019, 12:31:14 pm by coppercone2 »
 

Offline Rerouter

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #3 on: February 17, 2019, 12:38:32 pm »
Baking it will also remove the moisture, e.g. 100C in the oven for 10 minutes, sorry for not explaining that, once its heated, you just have to coat it before it cools too close to room temperature, e.g. 20C above ambient, the goal is just to reduce it. If its still warm from the weld, you get the same effect.

I don't know the exact metal your using, but even 200C will relieve some of the stresses in most carbon steels, but some can need quite a bit higher.
 

Offline coppercone2

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #4 on: February 17, 2019, 12:44:15 pm »
I don't know its some bolt I found in the parking lot like 10 years ago lol. Some giant 3 foot long bolt was just laying in a parking lot so I took it.

What time does it need? I set the toaster oven to its 1hr max and I measured its maximum something like 550C.

This does not need to be hard, I just don't want it to crack. I would like to be able to beat it back into shape if anything, but its horrendously over built.


Where do you get negligible softness benefit from heating? How many hours?
 

Offline Rerouter

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #5 on: February 17, 2019, 12:47:13 pm »
Steel bolt, so lets say some mid carbon steel, high strength without being too brittle,

Tempering would be about 240C for half an hour.
 

Offline AlfBaz

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #6 on: February 17, 2019, 12:56:55 pm »
Slightly off topic perhaps but somewhat relevant.
In metal work at school we turned up a knurled center punch.

If I remember correctly (it was nearly 40 years ago), hardening the tip involved heating it until it turned a soft red and then dunking it in water.
After that you had to polish the end, and hit it with a flame and as the colours came through, just as it went through the orange/yellow phase you dunked it in oil.
The first part was supposed to harden the mild steel and the second to relieve some stress and make the tip less brittle.

 

Offline AlfBaz

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #7 on: February 17, 2019, 01:00:41 pm »
Just re-read the first post, tempering, that's what it was
 

Offline IanB

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #8 on: February 17, 2019, 01:11:07 pm »
I welded a small tool together and I noticed that after you clean off the originally present oxide, and you heat for a while, it turns this really nice blue/purple/cyan color pattern.

Is this oxide layer stable? It's made out of a magnetic steel.

I thought it looks better then paint, my idea was to mix up some clear 2 part jewelry resin, vacuum degas it, then paint the tool with it.

I don't mean a gun bluing, I mean a cool psychadelic neon blue color (kind of like when tig welding is done nicely).

This is a standard workshop process in metalworking. Here is a video illustrating the procedure:


I'm not an EE--what am I doing here?
 

Offline coppercone2

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #9 on: February 17, 2019, 01:13:39 pm »
well, i really cleaned the whole thing up up to 120 grit with the anglegrinder up from a 36, and reheated it. It only turned blue where it was red hot from hot bending or welding. The handle that was not really messed with stayed shiny.
 

Offline David Hess

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #10 on: February 18, 2019, 10:36:06 am »
Do a search for "color case hardening".
 

Offline coppercone2

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #11 on: February 18, 2019, 12:20:20 pm »
its painted because its too much effort to get the entire thing red hot with a blow torch ATM.
When I make a kiln maybe.
 

Offline T3sl4co1l

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #12 on: February 18, 2019, 01:34:41 pm »
Yes, it oxidizes with time*temp, and as a surface effect it's highly dependent on surface finish and prep of course.  You need a very stable heating cycle to get a consistent color across an object.

It's an optical interference effect, the technical term is iridescent (not psychedelic). :)

Also, because it's an optical effect, any coatings on top of the oxide will affect its color.  So, finger prints change the effective thickness, and show up prominently as colored marks.  You'd have to lacquer the surface, which also improves corrosion resistance (as mentioned, it's no real protection to the metal).

Specifically, the oxide is either FeO or Fe3O4.  The former is unstable, but may be formed transiently, or on the interface layer (between Fe and Fe3O4), or at low temperatures, I'm not sure.  The latter is quite stable, well known for being the mineral magnetite.

Magnetite is well known for being a black mineral; it's quite lossy in the optical range, but not so much that a modest (sub-micron) layer doesn't reflect some off the base metal, and so you get interference colors.  The reflected wave is pretty much gone after two wavelengths, so as you continue heating, it goes from blue to a straw-ish gray, to the deeper and deeper blue-gray typical of iron scale.  (Thicker and thicker layers also tend to flake off from internal stress, making them that much less useful as coatings.)

Magnetite can indeed rust, and it's usually somewhat conductive, so, prone to the same electrochemical corrosion process that causes metallic iron to rust so quickly.  If nothing else, it is soft and pits easily, exposing the base metal.

Phosphating (bluing or Parkerizing) is a more reliable and protective method, but doesn't have iridescent colors as you vary the process (e.g., time*temp or chemical concentration), as far as I know.

Next best would be titanium, I guess? -- The anodize (and also from plain heating) has a voltage-controlled thickness, and the oxide is more transparent so the colors are brighter.  More expensive and harder to work, of course.

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Offline coppercone2

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Re: preserving cool blue/purple oxide layer on metal?
« Reply #13 on: February 18, 2019, 01:37:50 pm »
the iridescence was very patchy so I think psychadelic is an accurate term. It looked like a pink floyd concert light show because of all the grinder scratches (nothing was round, a bunch of flats colored to various shades of blue and purple). If it was solid blue I would NOT have been impressed by the finish enough to want to preserve it.

It looks like if you super polish it you can get a uniform color so long the crystal structure is the same (what clickspring does looks like colored anodization almost), but if you just go at it with a coarse grind stone heavy handed, you get a more unique effect (especially if you overheat it in certain places by applying too much pressure). Maybe of interest to people who like art. I mean you make it look like it was made with a chisel.

Not sure if people know how to get the 'cool' 70's look on it, when I look at examples online they usually want it very uniform so it looks almost like colored anodized. The welding marks are concentric colors (there is a obvious pattern to it based on heat gradients, this looks way different), if you do it with the grinder and overheat it in certain places it looks very patch work. You just need to work the metal like a complete goon to get this effect. Beat it up. A clogged grinding wheel might actually work even better so long you deep clean the oil/millscale off, because it won't cut as well and there will be more random heat. Also don't control the grinder too much and let it skip/vibrate a bit so you get uneven patterns, and don't hold it right either so the stone hits at weird angles. I got this because its weird shaped and I was already tired/pissed off and working at weird angles to just get the excessive arc weld off of it (I dislike this process compared to nice clean gas).
« Last Edit: February 18, 2019, 01:45:59 pm by coppercone2 »
 


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