What finish should I use for blades and knives?

[White Nomad]

So I've read through here a few times but I can't seem to find the answer to my question, so, what sort of etch/finish should I use for blades and knives that will prevent rusting but also not ruin the heat treatment? Also, if anyone can tell me how to blacken blades that would be appreciated, as well as if anyone has any information on russeting.
Thanks in advance.

[ThomasPowers]

Depends on the alloy, 440 C is pretty rust resistant but hard to blacken/russet. Can you narrow it down a bit?

[White Nomad]

I can, kind of. You see, I work with a lot of scrap steels due to all the illegal dumping that happens around where I live. There are a few individual pieces of steel I have ordered but outside of that all I can tell you is high carbon, low carbon, mild, wrought or rebar. 
Do you know of any finishes that would make high carbon show up as a black/dark grey?

[Irondragon Forge ClayWorks]

I've used cold bluing solution works pretty well but will wear off and needs retouching. I've also used mild acid (lemon juice or vinegar).

[White Nomad]

I've used Vinegar before but how does lemon juice (citric acid) show up?

[Irondragon Forge ClayWorks]

It turns the steel black/dark grey. I usually cut a lemon in half and rub it on the blade over several days till I get the look I want.

[White Nomad]

I see, I'll try that out.
Do you know of any other finishing compounds and etchs that can be made from raw materials/plants?

[Irondragon Forge ClayWorks]

I've used strong instant coffee to get a brownish finish. Soak the blade for a couple days.

[ThomasPowers]

Any of the finishes used on guns can be used on blades; though some I would not use on blades that will be in contact with food.

I've seen some mirror polished black finishes on blades at the Knifemakers Guild Show.  Hot blued as I recall.  Do you have access to something like "Firearm Blueing and Browning" by R. H. Angier?  (Wow, I picked up my copy used for about a US$1 Back a number of years ago!; Do they have something like ILL where you are at?)

Just for fun try boiling a polished and degreased blade in very strong black tea and see what colour you get on a plain carbon steel. (212 degF, 100 degC is way too cold to affect the temper; but make sure that the blade tip is not touching the bottom of the vessel where the "pot" may be hotter than the contents.)

Tannic acid can be made from plants.

[White Nomad]

Thanks for the suggestion. I've looked into the hot bluing and I think I might give it a try.
Does soaking in strong black tea work the same as soaking in coffee?

[ThomasPowers]

"When a group of researchers compared the tannin content of coffee with tea, they discovered that green coffee contains around 0.7% by weight in tannins, roasted coffee around 1.8%, and tea up to 3.7%."    from findanyanswer.com

[pnut]

I've gotten some nice blackened finishes by simmering a cleaned piece in hydrogen peroxide for about five minutes or until evenly rusted then cleaning with denatured alcohol and simmering in distilled water for about ten minutes then coating with wax. 

Pnut

[Frosty]

In general the higher the carbon content the less it will darken in the etch. Of course alloying metals can alter this considerably.

If you're using mystery steels you'll probably need to make test coupons and keep notes. Use the metals in your pattern welds grind to the finish you like and cut small coupons, say 1" lengths and etch. Vary: recipe, strength, time, temp, etc. and keep notes of every change.

Make ONE change at a time and test, making multiple change means you'll never know what did what.

Frosty The Lucky.

[pre6422hornet]

I use 80/20 of ferric chloride and white vinegar to achieve the grey etch below.  I primarily use 1084 and 8670 steel.  j

sand to 800/clean with acetone/clean with water and Dawn dishwashing soap/rinse/dry

4 min in the etching tank/take out and neutralize with windex, scrub blade with 0000 steel wool/dip in water and rinse/  dry off and repeat entire process. 

then I stonewash. 

these two are 8670

These are 1084

[Frosty]

Stonewash? 

Frosty The Lucky.

[pre6422hornet]

Yeah Frosty it is the craze it seems.  It gives the blade finish that worn look, especially after etching.  I use a rotary tumbler and some river rock from the.... river Haha.   Really simple.  Let the knife tumble for 4 or 5 minutes, rinse it off and it is done.  Almost all my knife orders are for a stonewashed finished.   I tend to prefer to let a knife gather its own battle scars, but as we all know there are people out their who would prefer to have that done when they purchase so they can look the part. 

Edited March 3, 2021 by Mod30
Remove excessive quote.

[Frosty]

xxxxxxx  <sigh> Make what sells or find a different profession is the reality of making a living making.

Frosty The Lucky.

[Cavpilot2k]

Hey all, I've been away from the forums for quite a while but still doing work. 

I recently experimented with using powdered citric acid mixed up to a 10% solution and heated to give a nice dark gray/black finish on a few pieces. 

It worked like hot vinegar only much, much better. My guess is because vinegar is usually only about a 5% acid. 

I'd say for darkening, the hot citric is almost as good as Ferric chloride with little to no mess and safe enough to pour down the drain. I have not tried actually etching with it, but I suspect it will work great. 

I had the citric for some stainless steel passivation on other projects. 

Plus, it doesn't smell up the room like hot vinegar. 

I'm interested if anybody else has tried it. I'm sold.