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Kevin Colwell

very easy way to get a blue finish on steel

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Hello Everyone, for once, I actually have a tip that I can share with others.

 

I found this by accident, but it works so well, I wanted to share.

 

So - one problem many of us face is that blued finish on fittings is really beautiful, but obtaining that finish requires caustic salts. You can use heat, but that is not as precise or as deep of a finish.

 

Cold blue like oxpho and others work somewhat, but they are more for touch-up.

 

Here is a simple way to get a blued finish on steel.

 

1. polish it very well

2. clean very well

3. quick dip in dilute FeCl (4:1) is what I use

4. rinse in cold running water and pat dry.

5. place in oven, preheated to between 420 and 500F. You can change the oven temp depending upon how "blue" you want the piece.

 

Normally, 430F cycling will lead to a bronze color. But, the oxides from the FeCl cause the steel to become a uniform, deep blue. It is much more consistent and deeper than cold bluing or using a torch to heat blue (at least for most of us).

 

Probably not as good as the salts, but cheap and not dangerous.

 

Try it - it works really well.

 

kc

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Hey Kevin,

Thanks for the great tip. Do you have to keep an eye on it or is there a certain amount of time you need to leave it in the oven? Wade

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Great tip, Kevin. I'll experiment with this.

 

Any idea how durable the finish is? The biggest problem with heat patinas is that they tend to be very thin and fragile. I like rust bluing because it's tough, but it's also time consuming.

Edited by Matt Bower

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Time - I was tempering something that I had first dipped to check the pattern when I discovered this. I have done from 30 minutes to 3 1-hour cycles, and I did not see any real difference after the first 30 minutes or so.

 

Durability - The finish seems more durable than cold bluing, just because you have a deeper layer of oxides. It is a little more durable than the effect that you get just from etching, because the heat seems to set the oxides.

 

I don't think it is any better than the bluing salts. It just puts a good layer of oxides on the steel that will then turn a uniform blue and set due to heat.

 

The rust-based finishes are probably a little more durable.

 

But, this is a good option when you want something better than cold blue and you don't have the salts.

 

kc

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Thanks for the tip.

Do you try to neutralize the FeCl at some point or just count on the water rinse?

Steve

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Kevin,

 

Any photos of the blued piece?

 

I've been using a paste type cold gun blue that seems to work a lot better than the liquid cold blue solution.

 

I'll give your technique a try and compare.

 

Thanks bud.

 

--Dave

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Kevin, thanks for the tips, looking forward to more comments and giving this a try.

 

Ive always tempered at 350F. No science arguments for 350, I was just told to temper at 350 a long time ago and always have. Is there any science to temper or not temper at 430F and how hot is to hot for tempering, whats the max temperature?

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Bryan, I believe he's using this for fittings, so it's OK to let appearance be the deciding factor in how hot to temper.

 

For blades -- if that's what you mean -- tempering everything at 350 is a bit too simplistic, unless you only make one kind and size of blade and only use one steel.

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Here is part of a 12" seax that I tempered about 420F (it is 1080 and 15n20), because the person I am selling it to wants to chop a lot with it. This pic was taken under a slightly yellow-bronze light filter, not with white light, the page behind is white paper, so use that to guage.

 

It is a blue/black at that temp. It is only polished on belt sander to 60 grit, so the finish would be a lot better if it was really polished. It may or may not be any better than the oxpho paste. It is easy and cheap, though. Dave, let me know what you find. I think it may be a little closer to black than the liquid cold blue.

 

I don't plan to leave this blue, I just did this to show what I meant.

 

I stumbled upon this trick the first time with a 16" blade that I wanted to see the pattern after quenching but before tempering. Lo and behold, the whole thing was supposed to be bronze and instead it was a blue/black...

 

Yes - normally, it will be for fittings, where you use desired color for the outcome rather than hardness.

 

OH YEAH - one other notable effect, even the smallest weld flaws become visible. They have scale in them, so they don't oxidize due to the FeCl, and so those areas stay bronze while the rest turns blue/black. This may or may not be a useful thing for some of us. It is humbling, in this case.

 

kc

Edited by Kevin (The Professor)

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I was always told to strictly avoid tempering to a blue colour. As far as I know you get the worst relation between flexibility and hardness. In german it is called "Blausprödigkeit" which could roughly be translated (word for word) as "blue-brittleness"

 

Therefore I would never, personally, use heat to get a blue patina. Even though the colour can be quite beautiful.

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Meisenmann,

 

You are, in general, correct. That is why I posted this technique - the whole point is that you get a blue color with much lower heat. So, you don't actually lose the hardness of the steel. The steel that was not dipped in ferric chloride was bronze, and tempered properly for a large chopping blade. The steel that was dipped on the ferric chloride was blue, but was still tempered the same as the other, IT JUST TURNS A DEEP, RICH, BLUE.

 

In general, you are right, you would not temper a knife to a blue color.

 

I must not have been really clear - this technique gives you a good blue finish (which is good by itself), and also lets you turn things blue without using so much heat that the hardness is lost (if you want to use this trick for a blade).

 

I don't really want to blue my blades, but I love blued fittings with light colored woods.

 

take care,

 

kc

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Hi Kevin,

I am still not clear if there is some ferric chloride left on the blade after the water rinse.

Is it the residue that achieves the patina? And if so, does it need to be neutralized to keep the blade from decay in the future?

I really love blued fittings and I am going to try this when time allows.

Thanks

Steve

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Steve,

 

no Ferric Chloride left. it is the oxides left behind by the etching action. I have done this with rinsing and wiping with water, and also with windex/wd40/detergent/water. I think I was over-reacting with the neutralizing and cleaning, but I was not sure if the wd40 would affect the process (and besides, it would smoke in the oven).

 

I have just dipped into FeCl (4:1) for about 20 seconds, rinse copiously and wipe whatever comes off easily, and then bake. I dont know why the oxides left behind by the etch turn blue at a lower temp than the ones formed on steel by just heat (or maybe it is just that you start with so many more oxide molecules this way???).

 

have fun,

 

kc

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Ah, I think I understand what is happening there.

 

You have to know that the tempering colour is due to a thin oxyde layer that builds during tempering. The resulting colour correlates with the thickness of that oxyde layer (physics and optics). If you have a thin oxyde layer at the beginning of tempering, the resulting layer after tempering is a tad thicker. So you get a blue blade while you really have only tempered to a bronze colour.

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Hey "Perfessor," thanks for the tip. I'm loggin' this one for future reference--sounds like a real good way

to do some bluing/blackening. Lord knows there's some metal I've been trying to tweak the color of. This sounds like

a right keen way of doin' 'er.

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Ah, I think I understand what is happening there.

 

You have to know that the tempering colour is due to a thin oxyde layer that builds during tempering. The resulting colour correlates with the thickness of that oxyde layer (physics and optics). If you have a thin oxyde layer at the beginning of tempering, the resulting layer after tempering is a tad thicker. So you get a blue blade while you really have only tempered to a bronze colour.

 

 

Thanks for the insight. Now, the process makes sense.

 

kc

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I understand now.

Thanks to everyone for the input

I have been etching some of my first twisted cable blades to reveal the pattern before I filework them , so I can "Let the steel speak to me"

Now I see an other door opening with this technique.

Maybe apply the FeCl in selected places for pattern highlights.

Thanks again

Steve

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Kevin,

 

Any photos of the blued piece?

 

I've been using a paste type cold gun blue that seems to work a lot better than the liquid cold blue solution.

 

I'll give your technique a try and compare.

 

Thanks bud.

 

--Dave

 

Hey Dave,

 

I'd been meaning to ask you what process you were using for your blackening. I'm going to try this one out as well...but the blue/black I've seen on your blades is just great!

 

Cris

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