When framing 3D objects we use a system called ‘floating’. We centre the object on a piece of mat board that is secured to adhesive foamcore for rigidity. We then stitch, or in some cases if the object is quite heavy, wire it onto the float. We then create a box like structure from foamcore that is raised to the required height, so there is a glass clearance from the object. It is important to use a sturdy wide or deep frame in 3D cases for 2 reasons.
UV clear glass and Museum glass are highly recommended for framing 3D objects. UV non-reflective glass, once raised, will diffuse the appearance of 3D items and therefore is best suited to 2D work.
Over the years we have framed several Venetian masks where our clients have recessed the final piece into their wall and lit it from above. It’s a real feature and easy to do, especially if you can recess it into a wall that backs onto a cupboard or cavity for example.