Reflection On Coin Pictures (From TPG Holders)

It's all in the lighting angle. The plastic will have a "hot spot" relative to the camera unless you totally diffuse the lighting, which isn't easy; you basically have to drag the whole affair into your bathroom and point every single light at the wall.

The easier way is to play with light location and angle until the bright spot is out-of-frame. You're going to need more angle that normally recommended.

This is a big problem with holdered coins in that the lighting angle needed to get best color from the coin is "specular", ie it reflects off the coin like a mirror. Luster on the other hand needs lower angles to get enough contrast between the "luster mirrors" and the rest of the coin surface. If you are imaging lustrous coins in holders, you are in luck and will be able to find the right angles with some practice. If you are trying to show color in a holdered coin, you will need to experiment a bit...