The Purpose of Using Mat Board for Picture Frames

Using a mat board for picture framing adds a colored border around the artwork helping to enhance the focus and presentation of the overall picture.   A framer might add to this process by adding multiple mats to enrich the framed subject. Most commonly, a neutral colored mat may be used as the outside border then a small accent color is used on the inside opening (as known as the Bevel) of the outside mat. In lieu of an accent mat, a framer might also add a filler, a decorative wood or silver/gold leafed finish insert that fits in between matting or inside a larger frame to draw the eye inwards to the subject being framed.  You can see how it is used in the images to the left.
Mat board serves as a protective barrier in a picture frame separating the glass from the artwork.  This creates air space for the subject helping to minimize the damaging effects of moisture should it condense on the inside of the glass. This is of the utmost concern when conservation framing is required.

Specialty mats can be created to enhance your art, but remember the framing should enhance your art not detract from it. That is why many times the best mat for your art is simple and subtle in the proper proportions.
 

Photo credit to Frametech Northwest