I have started doing celtic knots in my pens , i used aluminium as the inlay but when i sand it i get a grey marking in the surrounding wood. please help new to this game.
Soak (as in, pour it on, not dunk it in) the finished (but unsanded) blank in thin CA. That will prevent the aluminum dust from getting into the pores of the wood and staining it. You may need to do this more than once if you're a heavy-handed sander.
Another tip is to use stabilized wood. I avoid sanding these and use only a skew. Prior to that, I used CA as Dan mentioned, then started stabilizing instead. With all of this, it's still difficult to avoid.