Some more work done on this, about 5 hours of careful colour choice ... back and forth with pencil marks until I'm happy with the colours. So far I've used Dark Green, Dark Umber and Mid Terracotta on the background and numerous greens on the bottle itself. It needs to be nice and dark but I'd rather not use Black because I feel it somehow deadens the picture by 'killing off' the subtlety of the other background colours. After all, when you really look into dark shadows, they are rarely simply black are they? The paper colour choice also helps here of course. I think the drama is coming through nicely, hopefully I won't over do it!
I'm not layering colours on top of each other but using them alongside each other though obviously there is some overlap. For example, I'm doing the background quickly with a squiggly circular stroke, first one colour then other colours filling in the gaps. I like to work up the picture all at the same time so will do one bit and then keep revisiting other bits. For example, I lingered for a while working on the bottle neck ellipse (always difficult!) and then when my eyes started crossing with the intensity of it I moved away and worked on another part. I'll keep going back to that ellipse with a 'fresh eye' until I think it's about right.
I'll work a little more on the upper, dark areas of the bottle next and also sort out the foreground area which is looking a bit rough. What I don't want is a drawing that is too polished-looking ... or too 'sketchy' either. It's all about finding a good balance, I think.