Pour enough white vinegar to nearly fill the glass into a pot.
Simmer the vinegar, adding mustard, citrus shavings or any other acidic material that might further oxidize the steel.
Place your sharpened blade into the glass and gently pour the vinegar into the glass. Fill the glass just up to the hilt of the knife.
Use a long cotton swab or brush to rub oxidation off the knife and stir the vinegar frequently. Let it soak for at least 15 minutes.
Use a clean rag, running water and dish soap to clean any soot that remains from its vinegar bath.
Dry the blade and observe whether you want a deeper patina. If so, you can repeat this process several times or even wrap a rag soaked in vinegar around your blade and leave it that way for up to an hour.