meaning that the residue works as coating on the carbon steel to prevent from rust

Since this is a handmade product

A SABAKI knife is a knife suitable for butchering meat and fish

You can see the mark on wooden case

Total Length: 290mm (11

AZUMASYUSAKU Unagi eel knives 180 mm Edo type, Aogami steel no.2 Noodle knife meaning that the residue worksAZUMASYUSAKU Unagi eel knives 180 mm Edo type, Aogami steel no. 2 Size total length 290 mm(79x11. 4inch), Blade length 45 mm(1. 7inch), Weight 210g(4. 3oz) Material: Aogami steel (Blue steel no2) Made by craftman. For eel cooking. Item no. 4573200716454 Import duties; taxes and charges are not included in the item price or shipping charges. These charges are the buyer's responsibility.