I agree with WildCattle.
I remember seeing my Grandmother Card Wool. The cards I am familiar with were made of wood with one end of rows of short pieces of wire embedded therein. In carding the wool or cotton a pair was used & the mat'l sort of combed between them. As a machinist/modelmaker have used a file card numerous times, here of course you only use one & use the card to clean the teeth of the file.
In all of my reading over the years have never seen mention of using cardboard to scratch off a gun barrel in the browning/bluing process.
