I have an object (an antique book cradle, for what it's worth) set against a dark grey background.
I want to cut it out and set it against a solid black background.
Could someone please list the steps - or point me to a list of steps?
If you only have a photo, then it's as others have said a selection and masking job. The Quick Selection Tool (W) of CS6 does a reasonable first approximation, which can then further refined. Sometimes it is easier to select the background instead of the object and invert the selection afterwards.
Automatic selection works best if there is enough contrast/color difference, so you might want to make a duplicate layer and manipulate Channels/Curves/etc. to achieve such contrast, only to base the masking on. You can then later copy that mask to the original image layer.
Best would be to make a photograph of your object against a contrasting background, it would make the subsequent masking operation much easier/faster, or if a Black background is used you're already done.
Personally I often (did several this morning) use Photoshop's Quick Selection Tool for a first rough selection and add a few pixels Feathering, and create a masked layer from that, which I then refine in Topaz Remask, because that is more powerful (also when there is object/subject transparency involved) than the Photoshop selection tools.
Cheers,
Bart