Framing original backgrounds

I haven't been able to find any opinions on this, but I'm curious whether people frame their original production backgrounds with their cels, or make color copies for framing. I would imagine adding other painted surfaces to the inside of a frame would cause degredation to the cels over time. Any scientific opinions would be appreciated.

Thanks
-DHD

I've never framed an original background cel though it's b/c I do not possess any at the moment.

All of the cels I have framed are with original backgrounds. I doubt that you run any long term damage to your cels for 99% of backgrounds are done with water color paints so the only problem would come from the non acid free paper the background is made from. I "float" my cels between two mats so the cel does not touch the background.
I would think that should be enough protection for the only other problem might be from "gasses" released from the background over time. I would think that if you are careful not to allow your framed cel to be exposed to a lot of heat IE: in sunlight or displayed with an electric light illuminating the cel by beaming light directly on it such as those found in some art galleries you should not have such a problem.

Thanks JWR, it is the gasses that I am worried about. I also float my cels, but I'm wondering what will happen over time. I was thinking that a possible way to protect them would be to float a blank piece of celluloid over the background and below the painted cel thus isolating both from each other. Does that make any sense?