How Do You Actually Use A Gray Card With Coin Photos?

Thanks, jbuck. I used an index card as my temporary coin pedestal background, and you can definitely see that the camera makes it a hazy gray instead of white.

I assume you're using the Nikon D90, so here's how to do it with that camera. Go to White Balance in the shooting menu. Scroll down to PRE (preset manual). Select d-0, then press and hold the WB button on the back of the camera for a few seconds, until "Pre" flashes on the top display. Quickly take a photo of your gray card using the exact same lighting you'll use for coins. If you see "good" show on the display, you're WB is set for that particular lighting. This should largely eliminate the need for color adjustments in editing. If your lighting changes (from new lamp bulbs, a ceiling light, or daylight from a window), the color may be off slightly, so try to avoid lighting changes, or just reset the WB with the gray card again.

I usually do white balancing before but occasionally after shooting. Both my Canon and Sony tethering programs have white balance function, so it's easy to just put the gray card in place and press a button. If your tethering software doesn't have white balancing function, you should get different software.

I use Canon's Digital Photo Professional for simple post-processing tasks. It has a white balance "eyedropper" so is easy to white balance in post, but you need to make sure you have an accurate reference. When I know I'll be doing white balance in post I stick a gray sticker on the holder, or sometimes will even shoot the coin on top of a gray card as a background. Then just hit that area with the eyedropper and the whole photo is properly white balanced.

I have white black gray and tan.