Exhaust valve ceramic coating or deposits?

[Kurt Deschler]

I have the head off of my 5ktq to re-mount the EM and I am lapping the 
valves while it is off. There is a hard white substance on the exhaust 
valves. I would like to know if this is ceramic coating that should be 
kept or some kind of deposit that should be removed. When I did my 200tq, 
I left it on because I wasn't sure. Anyone know for sure?

 	-Kurt