Food safe scale?

[EastCompassoKnivery]

Hi! I'm looking in to making a Nakiri style knife soon and on this particular style of blade I find the black oxide scale left behind from heat treat looks rather wonderful, but is it food safe? Part of me thinks that it's not actually coming off into the food so it's fine but it's something j want to be sure on before I actually do it. Any info would be wonderful thanks!

 

[mete]

The oxide will be porous and collect things that add flavors ,bacteria . In the old days when I was a kid we knew how to wash knives - hot water and detergent or soap .

 

[tim37a]

If you are planning to use it in a commercial kitchen, I don't think an inspector will accept it.

 

[Stacy E. Apelt - Bladesmith]

It's been a while since my restaurant/kitchen days, but don't recall any inspector making a complaint about knives with the upper bevel in a rough finish. They do complain when any knife is left uncleaned.

Many high end Japanese blades have a rough upper bevel. Some are pretty black. I know several chefs who have purchased such blades from me and other makers, and none have expressed any concern.

As to your question, HT scale is iron oxide. It is not toxic. If it is actually scale, it will wear or flake off. If it is just the rough finish on the steel, it will hold up pretty well. I darken the upper bevel by soaking in FC and then finish the ha-ji.