Cleaning white silk on braces?

[kirsch]

Hello all,

I have some white Trafalgar braces, and the adjustable part is made of brass or something. They look really sharp, but the brass (or whatever metal it is) has left a brown mark on the white silk. The other day I went to adjust a little bit and realized that the smudge is very visible.

Any way to clean the slik?

thanks,
chris