Rust Bluing a Khukuri

K

-KJ-

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Sep 6, 2013
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I don't have my 17.5" chitlangi yet but I already know that I'll need a rust-resistant finish to keep my otherwise inderstructible blade from corroding into a heap of damp red flakes (seen it happen).

After researching until my eyes bled I decided to rust blue it. This is the most durable form of bluing, and is commonly used by hobby gunsmiths who don't have the money to invest in a fancy bluing cabinet.

To rust blue steel you need;

1: Time. If you don't have the time to boil a knife blade for 10-15 minutes after you get up and before you go to bed DON'T TRY THIS. You'll just pit and irrepairably damage a good knife.

2: A corrosive agent. You can use almost anything, but I want a finish like you get on a nice rifle, so I plan to go with Pilkington Classic American Rust Blue

3: Protectant. I don't plan on removing the handle, so I need to protect the brass from overapplied bluing chemicals. Laquer is apparently the standard protective coating, so I'll pick some (and some acetone) up at a local hardware store.

4. Tape to keep the protectant off the blade. I can think of nothing more annoying than a blade with a beautiful and even blue finish that starts 1/8" from the hilt. Painter's tape or electrician's tape preferred for clean removal.

5: A pot of distilled, de-ionized water. I'm not sure where I'll get this but I've heard that aquarium stores generally have it for about 40 cents a gallon.

6:degreaser. If your blade isn't clean of all oil it won't rust in a controlled, even manner. Alcohol is likely your best bet since it's cheap and shouldn't remove your laquer.

7: Carding Abrasive. Carding is removal of the excess "fuzz" from the blade after boiling, and is done every time the blade is rusted. The standard is degreased steel wool (you hear a lot about degreasing stuff), but rumor has it that scotchbrite pads are better (no grease to begin with)

8: Starting Abrasive. Should my first attempt turn out miserably I plan to restart the entire process after taking 400 grit sandpaper to the blade. Sumdood's experience in a metal shop class that covered rust bluing is that anything finer than 400 grit doesn't make for a good finish.
 
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Thank you. Can't wait to try it myself.
Laquer sounds better then what I would have used. Sticky tape :o
 
the process...

You prep your handle and degrease the blade, paint your bluing solution on evenly, wait 4-5 minutes, and paint a second layer.

You wait 12- 24 hours (depending on how shiny a finish you want), weep and gnash your teeth at the rusty orange abomination your blade has become, then boil it for 10-15 minutes.

You grimace at the fuzzy black abomination that comes out of the pot, then gently wipe all the "fuzz" off with your carding abrasive and reveal the amazingly attractive finish underneath. If you work too hard with the carding you'll scrape the bluing underneath off.

Congratulations! You've just completed the first pass! From now on you'll only need to paint one layer of bluing per pass! (typical rust blued guns take 7-8 passes to get truly "blue", and it may take up to 12 passes before steel will quit darkening.)

When you decide you've made your last pass, boil the blade one last time with some baking soda thrown into the water (to neutralize the acid solution) and then liberally coat with oil.

I may try this on some steel stock I have before I apply it to the khukuri. Haste makes waste, dont'cha know?:D
 
After actually receiving my knife I've decided that I can practice on the Karda and Chakmak first. they're the same steel and if they turn out acceptably I can move on to the khukuri without fear. Time to order some bluing solution.
 
Great idea to use the little knives first.
I'm still deciding which blueing solution to use. All have mixed reviews on Amazon. Might be that everybody used different kinds of steel or user error.
It doesn't seem complicated at all. Just takes a long time but nothing where we have to stand by and watch for hours.
Do you know if the solution is toxic? I was thinking of turning it into an "art project" for my two kids. They'll like it, me too and we get something useful out of it.
Thanks for your help and the very informative write up.
 
Cold blue (like oxpho-blue) is toxic and may leave traces of the toxins in question on the blade which is why I don't want to use it. Rust bluing solutions aren't toxic strictly speaking, but they ARE acidic. Unless your children are either over 10 or exceptionally well coordinated I'd suggest that you be the one who applies the solution and handles the pre-boiled blades. They can do the prep work and carding as long as they understand "No touch sharp edge!".:)
 
Jens, if you're doing this for the art factor, be aware that most bluing produces a streaked finish. The more passes you take the less defined the streaks get, but they'll still be there. We don't usually notice it because we're looking at blued guns and round barrels reflect light in streaks anyway.
 
There are several varieties of cold blue, browning and rust bluing. Brownell's has many of them. Oxpho, 44/40, the Birchwood Casey stuff, liquid and creams.
I seldom even bother with the boiling but warm with a hair dryer and sometimes not even that. I carefully degrease and don't get finger prints on the metal, wear gloves.
I often times even mix and match. Go with Oxpho, and then a pass with 44/40 or cream. Some will darken but leave the streaks you mention, others will help eliminate the streaks but not darken as well.
Just keep throwing the stuff on till you get what you want.

Just be sure to rinse thoroughly with hot water and oil the heck out of it when your done. Then watch it for a few days to make sure the bluing action has stopped. White spots or discoloration indicated it's still basically trying to rust your blade. A good rinse is all it takes.

I've never done a HI knife but I suspect it will take the bluing quite well.
Most of the cold bluing solutions won't do anything to brass. I'd of course not take the chance and protect it to be safe though.

Haven't done any bluing for awhile. Most of my solutions I'm sure are not much good anymore.
 
Good point about age vs. effectiveness Bawanna. In general the older a bluing solution is the less effective it is. It seems that most of them are quite chemically unstable, which is why lots of people used to go with home brews until nitric acid started getting hard to get ahold of. (Why don't they just ban 4140, 4150, and mild steel while they're at it - because someone could possibly build a sten out of them?) rant off.
 
I have no idea what you just said?

Cyanide? Ain't that kind of a bad thing. Isn't that the little pill secret agents where in a necklace to cross the river in a moments notice when things go like sideways.
 
It was something my old man used to do, take a bone mash and some potassium cyanide and cook it it leaves these cool multicolored designs on the steel? case hardening i think ? I see it all the time, I thought it was all done with that ;o

lol i am looking it up, its just a very vague memory but i remember cyanide being used in gun bluing or case hardening
 
Case hardening would probably ruin any differentially tempered blade. You'd be taking the exterior and randomly hardening it to different depths and harnesses (which is what makes color case hardening COLOR case hardening) while at best preserving the original temper in the very core of the blade and at worst annealing the innards so badly that it wouldn't be worth it. Case hardening in general is used when you don't know how to temper a part all the way through, and color case hardening is the least reliable and most decorative technique IIRC.

Short answer; Only if you you want a very pretty blade that'll chip like rock and then be impossible to resharpen once you grind the chips out.
 
neat kj you ever heard of cyanide being used in any metal treatments? or did i memory modify myself?
 
I can't say for sure, but i think some old bluing treatments used cyanide, and some other ones used mercury compounds. This was back in the day when "We don't think it does anything" meant that a product was safe and kids touring factories got to stick an arm in the mercury barrel.
 
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