Final answer:
The best option for mounting coins, medallions, or flat 3D objects is the shadow box due to its deep frame that accommodates the extra thickness of these items and enhances their visual appeal with a 'shadow' effect.
Step-by-step explanation:
Among the options provided, shadow box is the best choice for mounting coins, medallions, or relatively flat 3D objects. A shadow box is a type of picture frame with a deep frame that creates enough space between the glass and the backing material to display thicker objects. This creates a 'shadow' effect that enhances the visual appeal of the displayed items. They are often used for displaying objects that have depth and require protection, striking a balance between visibility and preservation.
On the other hand, a fillet is a small molding that fits inside a frame or mat and is primarily decorative. Float mounting is when an artwork is mounted on top of a mat board so that it appears to 'float' without touching the glass. Matting involves placing a thin, flat piece of paper or cardboard around the item to act as a border. While these methods can also be used for displaying flat objects, they do not provide the same level of depth and protection as a shadow box.