Re Black a Firearm's color (to black,) what is a good product to use for touch up?

[KnightExtreme]

Looking for a good easy to use product to reblacken a firearm? Any that good / durable and easy / simple to apply with no baking required?
Any suggestions?


Thanks,
KE

 

[Taudisio]

How much do you need to cover and what does it look like? Covered in rust? Just bare metal? Is it nitrided, blued, parkerized, or something else? I have often used the little sharpie for small touch-ups.
Can you post photos of what needs fixed?