I worked on this piece a little more yesterday and then decided to call it a day. I felt it had come to the point where any further tinkering would be counter productive.
My own thoughts on it at this point are, on the negative side that it has become very dark, perhaps too dark. On the positive side, it has taken on a quality which seems vaguely other worldly to me and one which might be called interesting. Perhaps I'm stretching it here!
Anyway, I gave it a couple of coats of varnish and called it a day.
I use an acrylic gloss varnish which protects the surface from dust and dirt over time. It also gives a depth and richness to the colours, especially the darker and metallic shades. For me, its a bit like taking a pot out of the kiln after a glaze firing when the colours that I have applied really come to life. I tend to choose darker colours in my paintings because I've always found them more interesting to work with and because facts are facts, the climate here is pretty wet and grey most of the time. (This is a subject which I try not to harp on about too much in general conversation because there is always the risk of it developing in to an extended moan which just puts everyone in a bad mood! )
Can a painting be off-puttingly dark?