Will boiling vinegar alter hardness of white steel?

I bought a nice usu nomi at an auction but the black oxide film from forging is gone. I'd like to make a new oxide layer and the easiest way to do it is by submerging the blade in boiling vinegar. But will this do anything to the hardness of the cutting layer? I think I should be okay seeing how I will never reach the temperature at which the blade was tempered with boiling vinegar.

Boiling vinegar is well below the temp that blades are tempered at. However I always assumed KU finish was from the oil quench, just like seasoning a CI pan.

I've seen this topic come up in a couple other threads.
This post, with a link to Dave's work, shows what cold blueing can do.

Pensacola Tiger said:

AFAIK, once it's gone, it's gone for good.

You could polish the KU finish off, and leave it to patina, or give it an etch or a cold blueing treatment, as Dave Martell did to a reconditioned Forgecraft: http://www.kitchenknifeforums.com/showthread.php/32000-Forgecraft-Upgrade

Click to expand...

I did a test run first with an oire nomi blade and just to be safe I brought the vinegar up to 80 degrees Celsius. I brought the vinegar up up temp, poured it in a glass, put the blade in it and I let it sit until the vinegar was at room temp. Then I cleaned the blade with a sponge and I repeated the process one more time. The soft steel now has a gunmetal grey colour. The white steel cutting layer turned a dark black so I'm leaving it like that on the ura. I wasn't expecting the gunmetal grey on the soft steel (must be because of the low carbon content) but actually I think it looks very nice and it should be enough to protect it against rusting.

That looks dope!!!!!! 😍😍😍

Anyone left a knife in boiling vinegar that long before? I've only done quick dunks and it left a really rough finish that added a ton of drag, but it smooth itself out with use.

I've done it with a carbon steel Morakniv. That one turned very dark just like the cutting layer on this blade. My guess is the higher the carbon content, the darker the oxide film.

That looks fantastic. I normally use bluing solution, but I might just have to try that on a couple of my nomi.

I chopped some hard white oak with the blade in the pic today to test of anything has changed and the hardness is unaltered. I already knew it was after a quick sharpening on my suita but the chopping confirmed it.