The plasterite that I make will not stay as shown my lady has already decided to paint them and have landscape pictures on them so yes paint them how ever you want, but no metallic paint.
AS far as the metal when I use some in it is a small amount such as a pinch of copper powder for a gallon volume, but lately I have not put any to see what would happen.
There is something of worth that was told me by Spirit Walker, if we can verify this it would show why Plasterite is working; what he said was that we probably have a gazillion microscopic air bubbles in the Plasterite, and that would translate into an infinite amount of resonant cavities 
That is big, we shall see, I will have to break a piece and look with a microscope, I think I have one that I can hook up to my computer, given to me by a long ago friend
As soon as we have painted pieces I shall post them