Tarnishing Nickel

I have a Nickel-plated T1 and I have been polishing it to keep it shiny, but I want to tarnish it. I know some people put it in Coke or something similar to force it to tarnish, but I don’t want to do that. So, my question is: How long will it take for the nickel to naturally tarnish?

Has anyone else done this with a T1? If so, please post pictures, because I want to see what the end product will look like.