I am wondering if anyone could give some advice for shooting and keying out where the subject is a plastic bottle.
The layout is hands in shot (greenscreen) picking up and moving the bottle around. The background has to be replaced so I need some of it to come through the bottle. I have read a way to do this is covering the back of the transparent object with a black material. Is this correct? or is there a better way?
That bears some testing, but very good keyers (such at the "Ultra Key" that is in Premiere) will do a decent job of keying through clear or semi clear objects and still leaving details. I've never used it for exactly that, but Ultra Key will still leave reflections in windows, etc., so it should work for that. As I said, bears testing.
In that case you'd just shoot with a solid greenscreen background, as normal. I've never heard of the putting-the-black behind something. I'm not even sure how that would work.
Fantastic Plastic Entertainment, Inc. fantasticplastic.com
It may work if instead of keying, you use a different composite blending mode. When you light something like a wine or beer bottle, it's a common trick to paste white paper across the back to bounce the light back forward from inside the bottle - I have my lava lamp treated this way and it makes the contents jump out well. With black, I'm imagining you're doing a luminance key and not chroma.
Think about two different chroma keys: one on the bottle and one for the background, in different colors.