Cleaning the outside of a Meer?

Here's the pics. I cleaned the inside with a pipe tool. I left a thin layer of the cake on so I wouldn't scratch the inside of the pipe itself. I am wondering though, how does it hurt the pipe to scrape the inside if it's made of stone? Not questioning the validity, it's just not very intuitive.

Parts of the pipe are showing the yellowing from smoking but the darker spots look like it's more dirty to me. Thanks for the help guys!

[Zanaspus]

I can't think of anything that won't also be harmful to the patina, but do this: Buy some beeswax from a craft store. Smoke a bowl of tobacco in the pipe, and while the pipe is still warm, rub the outside with the wax. Remove excess if there is any after the pipe cools.

This is something that should be done as a normal course of maintenance anyway. I suspect that after a couple of said treatments, you'll be happier with the look of the outside.