Turkey Fife,
It's not being worried about the little things. When you condition in only ONE direction, you are able to change pitch much more effectively and
consistently. For instance, when you run you're striker with the striations, you typically get a lower pitch, but then when you run it ACROSS the striations (i.e. going across the hills & dales) the pitch will change.
This change in direction is super critical for getting purrs that sound extremely life-like. If you condition your call in one direction, you will see a difference in the tone, pitch and resonance of your yelps and purrs...
I condition all of my calls with a fine grit emory cloth, and carry a cloth and a 3M pad in my vest. In my experience, slate and sla-tek (K&H) will typically need a re-surfacing every few days of the season, because the moisture does affect the surface. If you prefer glass, crystal or metal, these surfaces hold their striations very well and should last most of the season (pending striker material, of course
)
S&R