Metallic buttons are printed on acetate, a clear film used instead of paper. Acetate allows for the silver shell of the button to show where ever there is white in your design.   The image below illustrates the difference between a standard finish button and an acetate button. The image on top is of buttons produced with our standard finished. The bottom image shows the same design printed on our acetate finish.  Note that anything which is white in the design appears silver in the acetate button.