Short answer...... you know you need to "condition" your caller when your striker "slips" and makes no sound or complete calls.
They are called Friction calls, because the Striker stroked across the surface produces the sound. Slippage can be the surface of the pot call or the End of your striker. So protecting both from becoming soiled from your hands or other.... is part of how often they need to be conditioned or "dressed".
Glass and Crystal are not as likely to become "damaged" by excessive exposer to oils and other things like Slate. Slate will soak up and penetrate the surface and in some cases render it useless. While Glass and Crystal can be cleaned with 409 or simple window cleaner.
Prepping callers is mostly done before the hunt. Then carried as to protect both the caller and striker so a call can be done when desired. Most hunters do carry at least a piece of sandpaper, wire mesh or scotch bright pad..... just in case.
