Not all framing methods need to use the window mat effect, or when the mat opening frames a piece within the frame.  When framing an object or something that has mass and texture, depth is needed to support the piece and keep it away from the surface of the glass.  This is a shadowbox, as the depth within the frame creates a dramatic effect that forms a shadow inside the frame.  This method is not only used when framing objects.  An alternative to using the window mat style when matting a piece is called floating the work.

This gives the art a raise above the back matting, drawing the piece forward to the viewers eye.  This raise can be slight or severe depending on how deep the client wants the shadowbox to be and how much dimension is wanted inside the frame.  The effect of receding and then raising the piece back up to meet the viewer can be an interesting and unique method.  Not only does this style create depth, but it also allows the edges of the work to be exposed.  This is ideal for art on handcrafted paper or art that extends to the edge of the surface material.