[Gimp-user] change background in photo to grey scale

[PeterJWhite <forums gimpusers com>]

I'm brand new to GIMP. I photographed a bronze sculpture on an off-white paper
background in natural light. The shadow areas of the background range from white
to a peach color. I'd like to change the background to greyscale and then adjust
it separately from the sculpture. I've made a quick mask but now can't figure
out how to make the background a separate layer from the sculpture, so that I
can color correct the two layers independently. The sculptor wants to keep the
shadows in the background.

-- 
PeterJWhite (via www.gimpusers.com/forums)