Me Against The Dummy Button

You might want to consider using a photo gray background. That's what many experts suggest. It's also what I use. It helps with obtaining the right color balance. I'm not familiar with the coin you photo'd to know what the natural look is. Is it supposed to have luster...the coin looks very flat/dull?

When I change the white balance, I take a picture of a "pure" white sheet of paper on the approximate aperture and timing setting of the camera and the same lighting that I'll use. If anything changes I have to reshoot the paper. Then I tell the camera to use that shot as my reference for white balance. Is that how you do it?

Full stop, right there. That's the bottom line, and who cares what the setting are if the coin looks right?

Even with the best of equipment, you sometimes end up needing a little postprocessing. Any light leakage at all can affect color balance unless you shoot in a totally dark room, without even a computer monitor lit. I was talking to a professional photographer a few weeks ago, and he advised me that I should be using a hood over the lens even with direct-light macro photography. Any surface can bounce light to one degree or another, and that little amount is enough to affect color and contrast.

Your "21mm" shot is beautiful, and way too big. Size is the best way to compensate for lack of quality, and your shots do not lack quality. The goal of a 1000px final coin size, with focus and detail as sharp as your equipment is providing here, will allow you to back the camera off somewhat and achieve gains in lighting technique while still providing an image plenty big enough to grade from.

You're right, Prethen; the process I'm suggesting is one you only have to do *once* for a given camera/lighting setup. After that, the only difference might be a little angle on the light, or one instead of two, to cover the whole gamut from worn copper to lustrous silver with exposure being the only camera setting that changes. Even without the space to create a "permanent" shooting studio, I know that ISO 200, f/8.0 and about 1/125 is gonna be darn close right out of the box every time I set the rig up. I rarely do assembly-line shooting of a lot of coins, usually only one or two at a time, and if I don't shoot a grey card every time it's only because of laziness.

Since I'm postprocessing every "keeper" shot for cropping and sizing to post, it's a small additional effort to desaturate the Yellow channel to compensate for whatever minor color difference I had that day.