Spare Parts #12 - Heat Bluing A Set Of Steel Clock Hands

Heat Bluing A Set Of Steel Clock Hands, by Clickspring.

In this video I go through the process of bluing a set of steel clock hands.

Heat bluing of small steel parts is a key element of traditional clock and watchmaking. It can transform the appearance of even the most mundane parts, and is also believed to afford the parts a small measure of corrosion resistance.

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A very special thank you to patrons Dan Keen, and Rob Shearing.
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Abbreviated Transcript:

00:17 Generally its presented as 4 steps - Harden the part, Heat temper it to Blue, Polish the surfaces, and then Heat again for a cosmetic blue. But first things first, what is it about heating steel that makes it turn blue?
00:50 When full spectrum light strikes the surface, some is directly reflected by that oxide, and some passes through and is reflected by the underlying metal, and so travels a tiny bit further. The two waveforms are now slightly out of phase, and interact as they leave the upper surface.
01:06 Depending on the thickness of the film, some colors are cancelled, and what we see are those colors that remain. When the film is thin, we see a pale straw color. As the film gets thicker other colors are removed, and color we see gradually shifts from brown through purple to a rich blue.
01:24 This is known as thin film interference; its what causes the rainbow of colors in soap bubbles, and a very similar effect generates those fantastic iridescent colors you can see on some birds and insects.
01:37 In our case if we get everything right, the result is a magical deep blue color on our steel part, that no other process can quite match. And I should also mention that the result is not just a pretty blue color, but also a very reliable proxy for determining temperature, which we use during the tempering process in a moment.
01:55 So with a bit of the science behind the process in hand, we can make a few statements about what factors will affect the quality of the final blue color we're pursuing. For one thing it seems reasonable to expect that a uniform oxide thickness would give a uniform color, so it follows that we'll want to heat the part as uniformly as we can. I've made a dedicated set of bluing tools.
02:31 Any sort of contamination will not only affect
the way the oxide forms, but also the light reflection, so we want the work to be meticulously clean just before we start heating. Hardened steel will take a mirror polish much more readily than a soft steel. So the first step is to harden the work.
03:52 Once finished, that boric acid coating comes off very easily with a little boiling water. Now at the moment, the parts are glass hard, and much too fragile to be safely handled without risking breaking them, so I need to temper that hardness.
04:43 As it happens the temperature we want to temper
the work to, corresponds to the blue oxide color, a little over 300 degrees celcius, which is why you see the steel blued twice - once is for this tempering, and the second time at the very end, is just for the appearance. And you can see with this hour hand, just how sensitive the bluing process is to a temperature differential.
06:38 The final surface finish comes from using diamantine powder on a tin lap. Again with short moves to maintain the flat surfaces.
07:51 It pulls the last of the solvent residue from the surface, and leaves the parts quite clean. And you'll notice that I don't touch the parts with bare hands from here on, until the bluing is finished, to maintain that clean surface.
08:40 If the color has any sort of flaw, like for example you can see that the very tip of this hour hand doesn't quite go fully blue, then the part must be taken back to the previous polishing stage.
09:11 There are also several other factors that can affect the outcome too, beyond what I've mentioned here, including the composition of the steel, the ambient conditions, as well as the nature of the light being used to illuminating the part. All of this can be experimented with to further improve the final result.

Heat Bluing A Set Of Steel Clock Hands, by Clickspring.

[johnnyq]

Seeing the metal getting blue is just magic. Amazing work!

[BradReardon]

For not being a channel about physics, you did an EXCELLENT job of explaining thin-film interference to the layman. Can't wait for the next build video!

[adamcain]

I must have watched this a million times. I can't get over how perfectly you polished those radius. I have spent hours polishing metal punches at work to mirror finishes with horse hair and all types of compounds and stones. Your blueing finishes are stunning and look like they were clear coated.

[PracticalEngineeringChannel]

Awesome video. It would be cool to see the some of the heat processes with an IR camera.

[andreaquadrati]

Damn it Chris, it's the third time I watch all your vids about clockmaking. Stop being that skilled!

[markfryer]

Another AMAZING video from Clickspring. The level of craftsmanship, the quiet enthusiasm in Chris's narration, the quality of his video production. Little wonder this video has already been viewed over 55 K in just 24 hours with 4, 374 likes. But who in their right mind would watch such a video and dislike it? Those 15 people must be crazy.

[mikehoare]

What you are seeing here, is not only knowledge, it´s also talent

[wyldemanO]

Omg i love when these clickspring videos are uploaded!

[chadgdry]

that was a great explanation of the effort to blue with heat, I had no idea that level of prep was involved.. Cool

[bensthingsthoughts]

You would perfectly fit in Switzerland !! At our machining class we had to file an entire C clamp to shape, watching you filling with so much care, our instructors would have like you very much !!
Keep the great content coming !!

[karlish]

Thanks for the mini Science lesson, really interesting. Great video too, Cheers Chris.

[SlowlyLosinIt]

I'm just going to come out and say it. Chris, I want to personally thank you for making and showing us these outstanding projects/videos. No other artist in the world, with such talent would show anyone, their exact process of working on a piece of art. But you sir, show us, in detail, in DEPTH, what you learn, the best technique you find to do something while working on your projects. It's truly amazing, not only how high quality you videos are, but the quality of your work is. just....AMAZING. I love your videos, and you have an outstanding talent at what you do. I currently, do not have the money nor tools to make things like this, but one day, when I do, I will be using your methods. Again, no other artist would be willing to tell, yet alone SHOW, their process of creating a masterpiece. I thank you for actually teaching and showing us, your ways.

[AlexOvechkinSucks]

In 30 years from now, kids will be watching these videos in metal shop class thinking, cool, let’s try this, and it will be just as good then as it is now.

These videos are the definition of timeless.

[elidouek]

Chris your cinematic talent of making your shop feel so much bigger than it is is really amazing. Keep up the good work!

[markdebarr]

Beautiful parts, beautifully produced video. Why can't the mainstream broadcasters produce programming to this standard? Thanks for sharing.

[JayEllis]

Your clockmaking videos make me think I'm watching How Its Made, and I loved that series, and now I like this one!

[SublustrisRU]

Спасибо вам огромное за ваш труд! Впервые вижу настолько технически грамотное объяснение причин появления цветов побежалости. Продолжайте обязательно!

[RalphLBaer]

Exquisite. I could watch this meticulous sort of workmanship all day long.

[killerkane]

Chris, outstanding example of heat bluing! Once again you outdid yourself.

Su Amigo Siempre

[mechmotion]

I'm glad you post videos a few weeks apart. If it was any more frequent, I wouldn't be able to leave the computer. I'm looking forward to seeing the finished clock!