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Home bluing

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Home bluing

Unread postAuthor: inonickname » Fri Dec 25, 2009 9:38 pm

I need to apply a finish to a small number of parts and I'd like to try my hand at bluing them. (I know it doesn't provide much rust resistance, and better coatings are available). Small kits are available (cold bluing) and apparently the finish acquired from this is little more than paint-like. Larger kits are available for several hundred dollars (hot bluing).

After some searching around apparently the chemicals used in the process of hot bluing are fairly simple; potassium nitrate and sodium hydroxide as examples, with boiling water.

Does anyone have experience with a mix like this? Or what a good starting mix is to blue small parts (I'll probably just use a tupperware container to do it in).

I'll try the NaOH/KNO3 soon and let you guys know. Thanks :)
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Unread postAuthor: Heimo » Sat Dec 26, 2009 7:09 am

how a bout oil bluing, heat the part and then dip it in some oil

from a different forum

I tend to find the chemical 'bluing' tends to leave a more brownish finish, and isn't as rust-resistant.

The end color for heat bluing is going to depend on the temperature you actually take the metal to. If you overheat an area, it will tend to grey out. I tend to use a MAPP torch for bluing and oil quench the pieces. Start in one area and bring it up to temp and then work out from the spot to the total area you are trying to blue. Make sure you are in a WELL ventilated area as this generates LOTS of smoke if you oil-quench.

If you mess up, you can buff up the area in question and try to clean up the coloration. I recommend practicing a fair amount with this before you try it on something you care a lot about.


you can also read some about it here http://www.gunandgame.com/forums/powder-keg/25077-oil-blackening.html
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Unread postAuthor: inonickname » Sat Dec 26, 2009 9:30 am

A viable option, but then you run the risk of messing with the temper (much worse than a hot salt dip) and it will be difficult to get an even coverage over the entire part. Plus, if it isn't done perfectly uniformly you can induce a lot of stress into the part.

Not attributes you want in a part for an ETC, which is basically the highest demand you can place on any part. The parts will be exposed to high currents, substantially higher pressures and temperatures than normal firearms, and a bunch of electrolytes at the same time. Stresses aren't really an option.

Thanks for the idea though, it will work for a few parts that don't have the same stresses place on them.

On topic: I need a barrel for the thing. I'm thinking of a length of brakeline which will then be blued. The first length will have a stainless cover and I'm hoping the rest will be under stress for such a minuscle amount of time that it will survive. Given the nature of an ETC the barrel will need replacing fairly often.

Thanks though :)
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Unread postAuthor: Gippeto » Sat Dec 26, 2009 12:15 pm

Cold bluing can turn out fairly well if you take your time, get and keep the part clean.

First you have to deburr and polish the part, then it needs to be cleaned.

I use a mildly caustic solution. Wear your ppe...caustics aren't something to fool with. Okay?

Rinse the caustic away with hot water.

Repeat 3-4 times.

Rinse the part in HOT water, until the part is heated through.

Apply the cold blue solution HEAVILY, rubbing it into the surface.

Let sit until the bluing just starts to dry.

Rinse with the HOT water again. If you need to darken the piece some more, then re-apply the bluing solution.

If the part is dark enough for your tastes, quickly dry the water with compressed air and a rag.

Dip the entire part in automatic transmission fluid (Dexron 2).

Set the oil soaked part aside for a couple days. This gives the bluing a chance to "set".

Wipe off the atf, and give it a wipe with proper gun oil, and you're done.

This is a breech that I made and blued with the method described.

Image

If you run into problems with a "blotchy" appearance, the likely culprit was grease/oil still on the surface. This is why you should keep the gloves on, and wash/rinse the parts several times.

Good luck. :)
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Unread postAuthor: mark.f » Sun Apr 10, 2011 11:10 pm

Sorry to bump a very old thread, but I was wondering over this exact same problem today. My next project will probably be made entirely from DOM steel tubing, and painting just seems... wrong, as I'm really going for that "WWII-occupied-Europe-bicycle-shop-weapon" look. :wink:

After some searching, I've stumbled upon a very happy medium between hot and cold bluing. Far more durable than cold bluing, and cheaper than hot bluing, but a lot of work.

Here's the basic rundown:

[youtube]http://www.youtube.com/watch?v=VPD3GWqk-yE[/youtube]
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