Blueing Blues

I wanted to blue a thin (0.5mm) sheet of steel as a dial. ideally, this would be stainless as I can get it flatter (as shim) than normal mild. I consulted Google, the oracle of ages, who seemed to think you could, in fact do this.

I'm not sure I agree. And doubted it in the first place given that stainless is meant to not oxidise ...

I have three pieces of steel. One is known mild (not quite sure what breed), one is stainless 304 and one is the actual flat stuff of uncertain constituency.

the 304 is not magnetic, the mild is and the unknown is slightly.

I heated each up in my bluing tray. the mild blued ( ). the other two did not even when the temperature was way above what blued the mild. In fact in another test, I tried to blue a bit of the 304 and it would not. I took it off my tray and a few minutes after the heat was removed, dropped a piece of mild on it and it went dark straight away (past blue!).

The stainless does turn a rather attractive yellow gold colour (and some vestige of A-Level chemistry said chromium to me, though I couldn't tell you why).

Also, in an earlier test I got cross and blasted the 304 with the flame directly and that actually did turn it kind of blue.

So what's the score with blueing stainless? Can be done? Need more heat? Barking up the wrong tree? Should I be yellowing it instead?

I'm quite sure that the ME Oracles can be clearer the Mr Google!

Iain

Iain how about getting a thin sheet of titanium? That should blue up quite readily.

Does this help?

**LINK**

Stainless steel will not blue, the only way to colour S/S is acid etch and not always successful. Also not blue colour.

Fulmen - thank you for the link, which explains things well.

More particularly, it matches my 'experimental results', which is to say a straw ish colour at normal and higher steel bluing temperature and blue when you really heat it up!

Accurate 500 degrees C is beyond the capabilities of the tools and techniques I have, so I will be seeking a plan G (Plan B went by a few months ago!).

Thanks to Pete and Clive for your input as well.

Iain

If your part is less than about 3" across and you're anywhere near Kent Iain you could borrow my little furnace it'll hold 500degC to within about 10 degrees all day long.

Thanks, Pete, but God's country is a long way from Kent .

Not sure it's the direction I want to go in anyway, but I certainly wanted to understand it!

Iain

https://www.gasparini.com/en/blog/electrochemical-chemical-finishes-stainless-steel/

Doubtful any of those processes could be easily accomplished in the average M.E.'s shop Iain. Plus you would have to be very certain of the stainless type and grade your starting with. It also won't produce the blue color you mentioned. Various thicknesses of very flat steel shim stock can be obtained through numerous industrial tool suppliers. Depending of the surface area of your dial project, heat blueing while still keeping it from warping during the critical heating & quenching phase with thinner material could be extremely difficult though.

For mild steel there's also what's called rust bluing that doesn't seem all that well known by most M.E.'s today. Search for a video on Youtube titled 1 Hour Red Rust Bluing on a channel called thecogwheel. But again, it won't give you that heat blued color, but a deep black instead if that color might be acceptable enough instead. Prior to today's much quicker hot caustic blackening process, it was the traditional method used to blacken and obtain a much more durable and mostly rust resistant surface on items such as guns. That video does leave out a few and I think important details if your expecting the best possible quality. First the finer and more even your layers of rust are, the better your final finished surface will be. You really want the whole surface to look like it's covered in a really fine dusting of rust. Leave it too long while rusting and the surface finish will degrade due to larger rust pits forming. Possibly rusting of the steel in a closed container using the fumes from Hydrochloric or Nitric acid might be better? Really high quality rust bluing / blackening is and despite the videos title, very time consuming verses the obvious time savings and I think much nicer color that heat bluing produces.

"Stainless Steel" is more properly called "Corrosion Resistant Steel"

Hello Iain, If matt black is acceptable for your dials then the American company Armco developed a process during WW2 suitable for chromium nickel and chromium stainless steels, American patent 2,394,899. A coating of wax will give it some lustre.

You immerse the job in molten sodium dichromate at 388 to 398 deg. C. for 30 minutes, take out the work, allow it to cool, wash the salt off with tap water.

The work pieces were components for mine laying equipment and Garand rifles. I have used the process at home with very good results..

Armchair theorist Alert! I've no experience of trying to colour stainless steel(s), but have messed around with Se-chemistry products for touching up firearm finishes - with very variable results. Have a look at Wikipedia - 'Black oxide'. It seems that some stainless steels will colour satisfactorily.

Surely what Pete is talking about is Browning as I have mentioned earlier on another thread which is used by gunsmiths?

Like a lot of processes, there can be multiple terms used for the same end result. Browning / Rust Bluing appear to be at least similar if not the same thing. The way I understand the method and how it works, the rust starts out as common Ferrous Oxide, FE 2O3. Boiling the object in water converts that rust over to a Black Oxide, FE3 O4. Our use of the English language isn't all that precise or at times properly descriptive either. I suspect due to tradition and possibly historical reasons, any of the steel blackening processes really are misnamed and incorrectly called Browning or Bluing when the color they produce is a deep black. Many years ago I did see a single picture of a hand gun that was in fact a very beautiful deep blue color. Unfortunately there were no additional details about how that color was produced. So I know it can be done at least with some ferrous metals, I just don't know how.

I think browning is the correct term as its been done since we have had firearms

Terminological inexactitude abounds!

R H Angier's 'bible' on the subject is titled 'Firearm Blueing and Browning'. It was published in 1936. It seems that chemical browning dates back probably before the 1600s, and seems to have been a refined form of rusting, coating the iron with red/brown ferrous oxide. 'Temper blueing' was also used around the same time, the colour being produced by heating, giving the progressive oxide film build-up that we're familiar with - and as used by clock-makers - to get a distinct deep blue colour.

Nowadays, the commonest gun finish is chemical blackening, but it's still often loosely called blueing or browning. This finish can be obtained by boiling a rust-browned part in water. This converts the red/brown oxide to black oxide. Traditional rust-browning - or blueing - is a very tedious process indeed, but it's safe, for instance on shotguns, which are traditionally soft-soldered together.

Currently-available 'Cold blues' are commonly based on Selenium salt deposition, but are not durable, and the colour depth is often poor. However, it's a useful 'touch-up' process.

Angier provides numerous recipes for chemically colouring iron/steel, but most of them sound more like alchemy than elegant chemistry. Many are based on, or contain, arsenical or chromium compounds, and other nasties.

An easy, proper, black oxide finish can be got with a mixture of Sodium Hydroxide (8 parts) and Potassium Nitrate (5 parts) in water, the parts being boiled for about 10 minutes in it, at about 140 C, the boiling temperature determined by the mixture's water content. It's a nasty, hot, dangerous, corrosive mixture, so be careful, especially if needing to add more water, and good luck getting the chemicals. Needless to say, everything must be scrupulously cleaned and de-greased*. The coloured finish is then oiled and perhaps waxed. It's really the oil or wax that slows down any subsequent rusting process, because the oxide coat alone is porous.

(Neither I, nor the management of this forum will take any responsibility for anything that occurs as a result of this posting, and Angier's dead. You know the drill...)

* and if anyone thinks that a wipe down with acetone will properly de-grease a surface, they are sadly mistaken!

"Never seen a mainline loco with rustless steel frames", said Curly.

Many thanks for the additional information Kiwi. Getting the proper hot caustic blueing chemicals at least in North America isn't too tough from Brownells Gunsmithing Supplies. Fwiw, water quality depending on whats available out of anyone's domestic water supply and it's natural chemical composition can also greatly affect these processes. Most seem to recommend using either rain water or distilled if the water in the area does create any issues. While I've never done any hot caustic blueing, everything I've ever read always points out that even the fumes coming off a hot caustic solution will instantly start rusting any ferrous metal in the same room.

I see many on Youtube using those cold blueing solutions. As you pointed out and in my opinion, there in reality a poor and low durability replacement for blackening complete parts when compared to most other methods. And yes, the metal surface need to be absolutely clean as well.

Pete, you're quite right, distilled water is best, and cooking up the nasty soup is best done outside, standing upwind...

You mention a deep blue colour, seen in a picture. Yes, this is common, and an attractive feature of Smith & Wesson revolvers. Colt's revolvers look blacker - at least to my eyes. But the range of near-black shades on different guns is quite considerable. I once handled a S&W revolver that looked oddly 'wrong': it was too black. It transpired that it had been worked on and re-blued by the local, friendly gunsmith who showed me, and used, the method I described. The different recipes in Angier's book undoubtedly produce different 'colours', but their ingredients look like curry recipes, and are, I'm sure, more the result of 'ancient knowledge' than proper chemical research.

Yes possibly that hand gun I mentioned seeing a picture off was in fact heat blued Kiwi. If it was, then whoever did what was obviously custom metal finishing had to be a real expert to get the exact same shade of color on every part.

I'm most definitely not trying to throw Iain's thread off topic, but add some hopefully additional information that could be helpful to others here that may not be aware of it. I've had a deep interest in gunsmithing, the tooling & methods used and Model Engineering for more years than I'd care to add up. From that perspective, I'd have say gunsmithing and the high level of craftsmanship involved is in fact very closely related to Model Engineering. While I don't yet have the fourth book, I do have the first 3 Brownells have produced titled Gunsmith Kinks. Mine aren't handy at the moment, but I believe Gunsmith Kinks volume I contains somewhere around 45 pages of information about metal polishing and how it's "properly" done from the perspective of full time master polishers working for Smith & Wesson and others. And trust me, without that information, it's not nearly as simple, easy or intuitive as many M.E.'s seem to think.

There's been more than enough pictures in the M.E. magazines over the years showing models in the various UK exhibitions demonstrating that information alone could be highly useful. It might have been T.D. Walshaw who mentioned in one of my books about too many models in those exhibition's being "highly polished, yet still deeply scratched" to prove my point. I'd highly doubt anyone here purposely produces any work of poor quality, the real issue seems to be the correct information just isn't as available as it should be. As one example, a lathe seems like the ideal machine to use while polishing round parts, and at one time I mistakenly thought the same. Those Brownells books instead show it's not and why there's better, faster and easier methods using a simple length of 1" - 1.5" square tubing, some shop made adjustable for length sliding mounts, and a couple of straight shank live centers to spin the work on while each part is held at roughly 45 degrees to the wheel face and being driven by the polishing wheel doing the work. That way the surface ridges are being taken down to the deepest valley's and your not slowly polishing those valley's even deeper. Then as each finer polishing grit is used, the part is polished at an opposite 45 degree angle. I honestly can't recall any forum post anywhere that even mentions these techniques.

Just to say that I'm delighted to have my thread thrown of topic (not that it is exactly) and that this sort of diversion providing very detailed knowledge is one of the things I value in ME Forum discussions!

Iain