It is good to know these "tricks".
You can use a glass of Coca-Cola for the same purpose (to get that nice, "protective" patina),as well. Just submerge the blade of the knife (only) and let it sit there for overnight. To do fine adjustments of the cola level hang some facial tissue over the rim of the glass and let it absorb the excess liquid (then remove it from the glass).

 

Lets see a before and after pic

 

I shave every day with a carbon steel blade that was made before my grandfather was born.

It shines like a mirror.

The other vintage blades that I've picked up that have a "patina" are usually not far from rusting.

 

common knowledge my butt, i'll be the first to admit i didn't know that cool trick!

 

Some blades look realy good done like this, worth a try, I will try this myself. Here is a link so you can see what it will look like if you do it properly.(not my site but just a link)http://www.thehighroad.org/showthread.php?p=4358889

 

I've done this to my opinel No8 with a grape fruit for four hours and yes it does protect it from rust i did it about 3years ago and there is still no rust.
Although it can give a nice pattern i did it more so to protect my knife from rust.
It is a way of acid treating your blade.

There you go yorky added a picture for you.Opinel No8.

 

I found chilli sauce to give a good smooth finish. (the onion was a bit patchy in places.)

 

Gee' I'm gonna go try this soon! Looks really good.

 

Right heres the results on my well used Solingen Mercater carbon steel bladed folder. It spends it's whole life in my pocket and is used every day.
It has quite a high carbon content, so after yesterdays fishing trip where it got soaked in salt water a few time, then all night in my fishing clothes, it was looking very second hand.
No before pics but I am well impressed with how well tea and lemon cleaned it in only half an hour of soak time.
Not the clearest pics but you can see how smooth and clean the steel is now:

 

Never heard of any of this before TopTip YB thankyou

 

The Question wrote:
"common knowledge my butt, i'll be the first to admit i didn't know that cool trick!"

Ditto. Guess that makes me the second to admit I didn't know that cool trick. lol. Thank you.

 

I looked this up on the cutlery science website....and maybe I don't understand what i read. it appears that inducing patina causes the blades to blunt much faster than without it.....or did i read it wrong?


main site :
http://www.cutleryscience.com/reviews/blade_materials.html

i was looking up AUS - 8A stainless

reference to corrosion
http://www.cutleryscience.com/reviews/deerhunters.html#rust

The Deerhunters were sharpened including an edge reset, and finished with a DMT 600 grit rod set at 22 degrees. Again no significant difference in sharpness was noted among the blades testing the edge on quarter inch poly. The knives were dipped in lemon juice to a depth of a quarter inch from the edge. After a two hour soak the AUS-8A and VG-10 blade were not visibly effected and had no sign of corrosion and the edge bevel grinds lines were still clear under the magnification (20x). The D2 blade had a distinct patina in all the contact area and parts of the edge bevel were solid black with oxidation (~one cm long sections). Under magnification, the grind lines were blurred out, and the edge bevel showed frequent large irregularities where corrosion had removed significant amounts of metal (~10x greater than the micro teeth left by the DMT rod).

However when tested for sharpness on the poly, the blades showed similar performance and no significant blunting. Based on previous experience with corrosion soaking, this can be misleading as the edge can be significantly weakened by rust but still appear sharp. To test the full effect of corrosion the blades were used to cut sixteen pieces of hemp. The D2 Deerhunter was aggressive but much harder to pull through the hemp. The VG-10 and AUS-A8 blades showed similar aggression, but cut with much less force. The sharpness was again tested on quarter inch poly. Compared to the above hemp cutting, the VG-10 and AUS-8A Deerhunters showed a similar loss in sharpness and thus were not significantly effected by the lemon juice. However the D2 Deerhunter wore down much faster in use after being exposed to lemon juice and now blunted the fastest out of all three steels. It was now blunting twice as fast as the VG-10 blade, whereas it was holding its edge for twice as long without any corrosive effects

 

I found an old rust boy scout knife. Should I clean it first?

 

I didn't clean mine, and the solution ate right through every thing on the knife.

 

patina!

ok,

i own some wicked carbon steel knives.

small and large kabar,

river trader knife (roach belly)

andd a new cold steel bushman, which i have used and there is now black 'raised spots on the tip of the blade! what are these can any body tell me?

Also if i treat this blade by forcing a patina, how rust resistant will it become? is it very protected and i hardly will have to oil it ? one guy on youtube virtually stated that the carbon steel blade will never really rust with a proper patina (acid treatment).

Some hard facts would be superb!

 

I've no hard facts for you, only that for centuries people have had carbon steel blades.

Look at "old timer" hunting, butcher and cooking knives, they don't have shiny steel or protective coats of paint. Of course these knives are looked after (why wouldn't a person look after a knife?) but you'll notice they have a dull grey colour to them.

Of course modern coatings help protect a blade, but they come off eventually. Aesthetically speaking I don't like coatings and I think what was good for my grandfather is more than good enough for me.

 

The patina dark or black is Fe oxide. FeO. It can be considered a "god oxide" because is a passive oxide that protects steel to active oxidation (rust, is red-brown, Fe2O3) or corrosion.

Rust is active oxide and is not good oxide.

FeO have the simiar action to the oxide of the inox steel, CrO2. CrO2 protects the steel more effectively that FeO.

FeO is dark-black, CrO2 is invisible.

If you put a low alloyed stell into the Coca Cola you make a phosfatizing (Coca Cola cotain a loto of orthophosphoric acid). If you put a low alloyed steel into vinegr it will form quckly a layer of FeO (if the time is too logher can be form the rust. Fe2O3)

Regards