Paging joebw to the knife forum please, odd ZDP-189 "corrosion."

[Spoonrobot]

joebw did such an awesome job with my Coke/Kick problem, I've got another one for you.  

Here's what happened.

After reading about using Apple Cider Vinegar (heretofore known as ACV) to give ZDP-189 a nice golden patina I decided to dunk my Endura blade and see what would happen.

I submerged the freshly washed and dried blade tip down in a clean glass jar of ACV and left it overnight for about 11 hours. In the morning I removed it and promptly washed it under hot water with common dishsoap. While doing so a large amount of the finish on the tang came off in my hands as I washed. I'm curious if this is just corrosion typical of the steel or something else? (Perhaps sinister?)

Also, I'm very curious why the area of corrosion occurred where it did. No other corrosion was noted, although the blade did develop a slight patina all over and all the previous staining was removed. The corroded area itself feels rough and similar to a DLC coating, does not appear to have added any "depth" to the blade, that is, it's not pitting.


I used the black plastic pick to place the blade in and remove it from the ACV.









I don't mind the corrosion, it doesn't appear to affect the knife operation in any way. Just something interesting that happened.

[Benner]

That is a bit odd.

[Nutznboltz]

My guess would be that whatever lubrication was used on that pivot area has impregnated into the steel (all steel is pourus) and either prevented the patina to take or reacted with the acv.  Regardless of how well you cleaned the blade it would be almost impossible to remove all the traces of lubricant in the tang.

[DaveK]

Lol. Only Spoonrobot would consider bathing an expensive knife in vinegar

Myself, I very glad that he does, as I know (amongst other things) not to wash my Kick in Coke, or my Spydies in vinegar!

Did you see any images of the end product (i.e. the patina you were after) before trying it Spoon?

[Anthony]

I thought Spyderco blades were polished to get that finish, not coated 

[Spoonrobot]

Did you see any images of the end product (i.e. the patina you were after) before trying it Spoon?

Nope, I think the poster Deacon over at the Spyderco forums recommended it but no one actually posted any pics. Which I suppose makes me a little too open to suggestion.   

I thought Spyderco blades were polished to get that finish, not coated

I think they are too, it's just hard to explain it in proper terms.

I can buy into the tang holding some of the previous oils and such theory but still don't understand why the reaction would occur the way it did if that was the case. Could there possibly be some sort of differential hardening on the tang since it has a lock interaction mechanism?

[joebw]

Hi Spoonie,

I think your differential hardening thought is the most logical,  It may be that the ZDP-189 needs greater hardness in the tang that would be detrimental to resharpening the blade. 

Cheers - Joe

[jzmtl]

Well there's only one way to find out, try it on another ZDP blade and see if the same thing happens.