While back I found a product called Bit & Blade Cleaner. It works good for cleaning your drill bits, chisels, plane blades, etc. but I find it works absolutely the best for cleaning a knife blade! Sometimes when I I think I need to sharpen a knife, if I clean it with Bit & Blade Cleaner I often don't need to sharpen it!
I use this stuff on a daily, no more like an hourly basis! This stuff is is a must-have if you use your knives much at all!
I didn't know how it would work on an old knife, so I got three old knives that I picked up the Oregon show. I cleaned the blade off with the Bit & Blade Cleaner and the blade got noticeably lighter colored and the rag got dirty.
See the before and after pictures below.
I use the product by spraying it on a piece of cotton rag and rubbed each side of the blade got more than 30 seconds per side. I didn't have to rub it a hard, I just let the product do the work and wiped it off. The stuff does not hurt if you get on your hands, I didn't wear gloves, though I probably should have.
You can buy it here : https://www.ptreeusa.com/shop_cleaners.htm
You can save about a buck on it if you buy it here: https://www.woodworkingshop.com/search. ... de+Cleaner
I wished I had saved the rag and showed you what it looks like after cleaning off just one side. Pay particular attention to the blade right in front of the handle, you can see some of the build up there in the before pictures but it's going to me after pictures!
What I thought was patina on both of the knives that I cleaned was actually dirt!
I'm glad I didn't use that old knife with the patina to cut a nice piece of pie or slice a roast!